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| author | Guido van Rossum <guido@python.org> |
|---|---|
| date | Wed, 27 Nov 1996 15:24:34 +0000 |
| parents | e52054440efc |
| children | 961bf9a200dd |
| rev | line source |
|---|---|
| 1529 | 1 Subject: FAQ: Python -- an object-oriented language |
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2 Newsgroups: comp.lang.python,comp.answers,news.answers |
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3 Followup-to: comp.lang.python |
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4 From: guido@cnri.reston.va.us (Guido van Rossum) |
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5 Reply-to: guido@cnri.reston.va.us (Guido van Rossum) |
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6 Expires: Sun, 1 Dec 1996 00:00:00 GMT |
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7 Supersedes: <DxJ3t1.CJv@cwi.nl> |
| 1529 | 8 Approved: news-answers-request@MIT.Edu |
| 9 | |
| 10 Archive-name: python-faq/part1 | |
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11 Submitted-by: Guido van Rossum <guido@cnri.reston.va.us> |
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12 Version: $Revision$ |
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13 Last-modified: $Date$ |
| 1529 | 14 |
| 15 This article contains answers to Frequently Asked Questions about | |
| 16 Python (an object-oriented interpreted programming language -- see | |
| 17 the answer to question 1.1 for a short overview). | |
| 18 | |
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19 Copyright 1993-1996 Guido van Rossum. Unchanged electronic |
| 1529 | 20 redistribution of this FAQ is allowed. Printed redistribution only |
| 21 with permission of the author. No warranties. | |
| 22 | |
| 23 Author's address: | |
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24 Guido van Rossum |
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25 C.N.R.I. |
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26 1895 Preston White Drive |
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27 Reston, VA 20191 |
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28 U.S.A. |
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29 Email: <guido@python.org>, <guido@cnri.reston.va.us> |
| 1529 | 30 |
| 31 The latest version of this FAQ is available by anonymous ftp from | |
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32 <URL:ftp://ftp.python.org/pub/python/doc/FAQ>. It will also be posted |
| 2048 | 33 regularly to the newsgroups comp.answers <URL:news:comp.answers> and |
| 34 comp.lang.python <URL:news:comp.lang.python>. | |
| 1529 | 35 |
| 2048 | 36 Many FAQs, including this one, are available by anonymous ftp |
| 37 <URL:ftp://rtfm.mit.edu/pub/usenet/news.answers/>. The name under | |
| 38 which a FAQ is archived appears in the Archive-name line at the top of | |
| 39 the article. This FAQ is archived as python-faq/part1 | |
| 40 <URL:ftp://rtfm.mit.edu/pub/usenet/news.answers/python-faq/part1>. | |
| 1529 | 41 |
| 42 There's a mail server on that machine which will send you files from | |
| 43 the archive by e-mail if you have no ftp access. You send a e-mail | |
| 2048 | 44 message to <mail-server@rtfm.mit.edu> containing the single word help |
| 45 in the message body to receive instructions. | |
| 1529 | 46 |
| 47 This FAQ is divided in the following chapters: | |
| 48 | |
| 49 1. General information and availability | |
| 50 2. Python in the real world | |
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51 3. Building Python and Other Known Bugs |
| 1529 | 52 4. Programming in Python |
| 53 5. Extending Python | |
| 54 6. Python's design | |
| 55 7. Using Python on non-UNIX platforms | |
| 56 | |
| 57 To find the start of a particular chapter, search for the chapter number | |
| 58 followed by a dot and a space at the beginning of a line (e.g. to | |
| 59 find chapter 4 in vi, type /^4\. /). | |
| 60 | |
| 61 Here's an overview of the questions per chapter: | |
| 62 | |
| 63 1. General information and availability | |
| 64 1.1. Q. What is Python? | |
| 65 1.2. Q. Why is it called Python? | |
| 66 1.3. Q. How do I obtain a copy of the Python source? | |
| 67 1.4. Q. How do I get documentation on Python? | |
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68 1.5. Q. Are there other ftp sites that mirror the Python distribution? |
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69 1.6. Q. Is there a newsgroup or mailing list devoted to Python? |
| 2048 | 70 1.7. Q. Is there a WWW page devoted to Python? |
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71 1.8. Q. Is the Python documentation available on the WWW? |
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72 1.9. Q. Is there a book on Python, or will there be one out soon? |
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73 1.10. Q. Are there any published articles about Python that I can quote? |
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74 1.11. Q. Are there short introductory papers or talks on Python? |
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75 1.12. Q. How does the Python version numbering scheme work? |
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76 1.13. Q. How do I get a beta test version of Python? |
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77 1.14. Q. Are there copyright restrictions on the use of Python? |
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78 1.15. Q. Why was Python created in the first place? |
| 1529 | 79 |
| 80 2. Python in the real world | |
| 81 2.1. Q. How many people are using Python? | |
| 82 2.2. Q. Have any significant projects been done in Python? | |
| 83 2.3. Q. Are there any commercial projects going on using Python? | |
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84 2.4. Q. How stable is Python? |
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85 2.5. Q. What new developments are expected for Python in the future? |
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86 2.6. Q. Is it reasonable to propose incompatible changes to Python? |
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87 2.7. Q. What is the future of Python? |
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88 2.8. Q. What is the PSA, anyway? |
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89 2.9. Q. How do I join the PSA? |
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90 2.10. Q. What are the benefits of joining the PSA? |
| 1529 | 91 |
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92 3. Building Python and Other Known Bugs |
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93 3.1. Q. Is there a test set? |
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94 3.2. Q. When running the test set, I get complaints about floating point |
| 1529 | 95 operations, but when playing with floating point operations I cannot |
| 96 find anything wrong with them. | |
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97 3.3. Q. Link errors after rerunning the configure script. |
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98 3.4. Q. The python interpreter complains about options passed to a |
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99 script (after the script name). |
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100 3.5. Q. When building on the SGI, make tries to run python to create |
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101 glmodule.c, but python hasn't been built or installed yet. |
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102 3.6. Q. I use VPATH but some targets are built in the source directory. |
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103 3.7. Q. Trouble building or linking with the GNU readline library. |
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104 3.8. Q. Trouble with socket I/O on older Linux 1.x versions. |
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105 3.9. Q. Trouble with prototypes on Ultrix. |
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106 3.10. Q. Other trouble building Python on platform X. |
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107 3.11. Q. How to configure dynamic loading on Linux. |
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108 3.12. Q: I can't get shared modules to work on Linux 2.0 (Slackware96)? |
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109 3.13. Q: Trouble when making modules shared on Linux. |
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110 3.14. Q. How to use threads on Linux. |
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111 3.15. Q. Errors when linking with a shared library containing C++ code. |
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112 3.16. Q. I built with tkintermodule.c enabled but get "Tkinter not found". |
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113 3.17. Q. I built with Tk 4.0 but Tkinter complains about the Tk version. |
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114 3.18. Q. Link errors for Tcl/Tk symbols when linking with Tcl/Tk. |
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115 3.19. Q. I configured and built Python for Tcl/Tk but "import Tkinter" |
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116 fails. |
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117 3.20. Q. Tk doesn't work right on DEC Alpha. |
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118 3.21. Q. Several common system calls are missing from the posix module. |
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119 3.22. Q. ImportError: No module named string, on MS Windows. |
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120 3.23. Q. Core dump on SGI when using the gl module. |
| 1529 | 121 |
| 122 4. Programming in Python | |
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123 4.1. Q. Is there a source code level debugger with breakpoints, step, |
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124 etc.? |
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125 4.2. Q. Can I create an object class with some methods implemented in |
| 1529 | 126 C and others in Python (e.g. through inheritance)? (Also phrased as: |
| 127 Can I use a built-in type as base class?) | |
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128 4.3. Q. Is there a curses/termcap package for Python? |
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129 4.4. Q. Is there an equivalent to C's onexit() in Python? |
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130 4.5. Q. When I define a function nested inside another function, the |
| 1529 | 131 nested function seemingly can't access the local variables of the |
| 132 outer function. What is going on? How do I pass local data to a | |
| 133 nested function? | |
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134 4.6. Q. How do I iterate over a sequence in reverse order? |
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135 4.7. Q. My program is too slow. How do I speed it up? |
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136 4.8. Q. When I have imported a module, then edit it, and import it |
| 1529 | 137 again (into the same Python process), the changes don't seem to take |
| 138 place. What is going on? | |
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139 4.9. Q. How do I find the current module name? |
| 2048 | 140 4.10. Q. I have a module in which I want to execute some extra code |
| 141 when it is run as a script. How do I find out whether I am running as | |
| 142 a script? | |
| 143 4.11. Q. I try to run a program from the Demo directory but it fails | |
| 144 with ImportError: No module named ...; what gives? | |
| 1942 | 145 4.12. Q. I have successfully built Python with STDWIN but it can't |
| 146 find some modules (e.g. stdwinevents). | |
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147 4.13. Q. What GUI toolkits exist for Python? |
| 1942 | 148 4.14. Q. Are there any interfaces to database packages in Python? |
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149 4.15. Q. Is it possible to write obfuscated one-liners in Python? |
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150 4.16. Q. Is there an equivalent of C's "?:" ternary operator? |
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151 4.17. Q. My class defines __del__ but it is not called when I delete the |
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152 object. |
| 2048 | 153 4.18. Q. How do I change the shell environment for programs called |
| 154 using os.popen() or os.system()? Changing os.environ doesn't work. | |
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155 4.19. Q. What is a class? |
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156 4.20. Q. What is a method? |
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157 4.21. Q. What is self? |
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158 4.22. Q. What is a unbound method? |
| 2048 | 159 4.23. Q. How do I call a method defined in a base class from a derived |
| 160 class that overrides it? | |
| 161 4.24. Q. How do I call a method from a base class without using the | |
| 162 name of the base class? | |
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163 4.25. Q. How can I organize my code to make it easier to change the base |
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164 class? |
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165 4.26. Q. How can I find the methods or attributes of an object? |
| 1942 | 166 4.27. Q. I can't seem to use os.read() on a pipe created with os.popen(). |
| 167 4.28. Q. How can I create a stand-alone binary from a Python script? | |
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168 4.29. Q. What WWW tools are there for Python? |
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169 4.30. Q. How do I run a subprocess with pipes connected to both input |
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170 and output? |
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171 4.31. Q. How do I call a function if I have the arguments in a tuple? |
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172 4.32. Q. How do I enable font-lock-mode for Python in Emacs? |
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173 4.33. Q. Is there an inverse to the format operator (a la C's scanf())? |
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174 4.34. Q. Can I have Tk events handled while waiting for I/O? |
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175 4.35. Q. How do I write a function with output parameters (call by reference)? |
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176 4.36. Q. Please explain the rules for local and global variables in Python. |
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177 4.37. Q. How can I have modules that mutually import each other? |
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178 4.38. Q. How do I copy an object in Python? |
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179 4.39. Q. How to implement persistent objects in Python? (Persistent == |
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180 automatically saved to and restored from disk.) |
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181 4.40. Q. I try to use __spam and I get an error about _SomeClassName__spam. |
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182 4.41. Q. How do I delete a file? And other file questions. |
| 1529 | 183 |
| 184 5. Extending Python | |
| 185 5.1. Q. Can I create my own functions in C? | |
| 186 5.2. Q. Can I create my own functions in C++? | |
| 1663 | 187 5.3. Q. How can I execute arbitrary Python statements from C? |
| 188 5.4. Q. How can I evaluate an arbitrary Python expression from C? | |
| 189 5.5. Q. How do I extract C values from a Python object? | |
| 190 5.6. Q. How do I use mkvalue() to create a tuple of arbitrary length? | |
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191 5.7. Q. How do I call an object's method from C? |
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192 5.8. Q. How do I catch the output from print_error()? |
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193 5.9. Q. How do I access a module written in Python from C? |
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194 5.10. Q. How do I interface to C++ objects from Python? |
| 1529 | 195 |
| 196 6. Python's design | |
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197 6.1. Q. Why isn't there a switch or case statement in Python? |
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198 6.2. Q. Why does Python use indentation for grouping of statements? |
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199 6.3. Q. Why are Python strings immutable? |
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200 6.4. Q. Why don't strings have methods like index() or sort(), like |
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201 lists? |
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202 6.5. Q. Why does Python use methods for some functionality |
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203 (e.g. list.index()) but functions for other (e.g. len(list))? |
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204 6.6. Q. Why can't I derive a class from built-in types (e.g. lists or |
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205 files)? |
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206 6.7. Q. Why must 'self' be declared and used explicitly in method |
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207 definitions and calls? |
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208 6.8. Q. Can't you emulate threads in the interpreter instead of |
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209 relying on an OS-specific thread implementation? |
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210 6.9. Q. Why can't lambda forms contain statements? |
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211 6.10. Q. Why don't lambdas have access to variables defined in the |
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212 containing scope? |
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213 6.11. Q. Why can't recursive functions be defined inside other functions? |
| 1942 | 214 6.12. Q. Why is there no more efficient way of iterating over a dictionary |
| 215 than first constructing the list of keys()? | |
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216 6.13. Q. Can Python be compiled to machine code, C or some other language? |
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217 6.14. Q. Why doesn't Python use proper garbage collection? |
| 1529 | 218 |
| 219 7. Using Python on non-UNIX platforms | |
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220 7.1. Q. Is there a Mac version of Python? |
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221 7.2. Q. Are there DOS and Windows versions of Python? |
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222 7.3. Q. Is there an OS/2 version of Python? |
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223 7.4. Q. Is there a VMS version of Python? |
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224 7.5. Q. What about IBM mainframes, or other non-UNIX platforms? |
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225 7.6. Q. Where are the source or Makefiles for the non-UNIX versions? |
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226 7.7. Q. What is the status and support for the non-UNIX versions? |
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227 7.8. Q. I have a PC version but it appears to be only a binary. |
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228 Where's the library? |
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229 7.9. Q. Where's the documentation for the Mac or PC version? |
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230 7.10. Q. The Mac (PC) version doesn't seem to have any facilities for |
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231 creating or editing programs apart from entering it interactively, and |
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232 there seems to be no way to save code that was entered interactively. |
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233 How do I create a Python program on the Mac (PC)? |
| 1529 | 234 |
| 235 To find a particular question, search for the question number followed | |
| 236 by a dot, a space, and a Q at the beginning of a line (e.g. to find | |
| 237 question 4.2 in vi, type /^4\.2\. Q/). | |
| 238 | |
| 239 | |
| 240 1. General information and availability | |
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241 ======================================= |
| 1529 | 242 |
| 243 1.1. Q. What is Python? | |
| 244 | |
| 245 A. Python is an interpreted, interactive, object-oriented programming | |
| 246 language. It incorporates modules, exceptions, dynamic typing, very | |
| 247 high level dynamic data types, and classes. Python combines | |
| 248 remarkable power with very clear syntax. It has interfaces to many | |
| 249 system calls and libraries, as well as to various window systems, and | |
| 250 is extensible in C or C++. It is also usable as an extension language | |
| 251 for applications that need a programmable interface. Finally, Python | |
| 2048 | 252 is portable: it runs on many brands of UNIX, on the Mac, and on PCs |
| 253 under MS-DOS, Windows, Windows NT, and OS/2. | |
| 1529 | 254 |
| 255 To find out more, the best thing to do is to start reading the | |
| 256 tutorial from the documentation set (see a few questions further | |
| 257 down). | |
| 258 | |
| 259 1.2. Q. Why is it called Python? | |
| 260 | |
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261 A. Apart from being a computer scientist, I'm also a fan of "Monty |
| 1529 | 262 Python's Flying Circus" (a BBC comedy series from the seventies, in |
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263 the -- unlikely -- case you didn't know). It occurred to me one day |
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264 that I needed a name that was short, unique, and slightly mysterious. |
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265 And I happened to be reading some scripts from the series at the |
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266 time... So then I decided to call my language Python. But Python is |
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267 not a joke. And don't you associate it with dangerous reptiles |
| 2048 | 268 either! (If you need an icon, use an image of the 16-ton weight from |
| 269 the TV series or of a can of SPAM :-) | |
| 1529 | 270 |
| 271 1.3. Q. How do I obtain a copy of the Python source? | |
| 272 | |
| 2048 | 273 A. The latest complete Python source distribution is always available |
| 274 by anonymous ftp, e.g. | |
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275 <URL:ftp://ftp.python.org/pub/python/src/python1.3.tar.gz>. It is a |
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276 gzipped tar file containing the complete C source, LaTeX |
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277 documentation, Python library modules, example programs, and several |
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278 useful pieces of freely distributable software. This will compile and |
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279 run out of the box on most UNIX platforms. (See section 7 for |
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280 non-UNIX information.) |
| 2048 | 281 |
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282 Sometimes beta versions of a newer release are available; check the |
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283 subdirectory "beta" of the above-mentioned URL (i.e. |
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284 <URL:ftp://ftp.python.org/pub/python/src/beta/>). (At the time of |
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285 writing, beta3 for Python 1.4 is available there, and should be |
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286 checked before reporting problems with version 1.3.) |
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287 |
| 2048 | 288 Occasionally a set of patches is issued which has to be applied using |
| 289 the patch program. These patches are placed in the same directory, | |
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290 e.g. <URL:ftp://ftp.python.org/pub/python/src/patch1.1.1>. (At the time |
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291 of writing, no patches exist.) |
| 2048 | 292 |
| 293 An index of said ftp directory can be found in the file INDEX. An | |
| 294 HTML version of the index can be found in the file index.html, | |
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295 <URL:ftp://ftp.python.org/pub/python/index.html>. |
| 1529 | 296 |
| 297 1.4. Q. How do I get documentation on Python? | |
| 298 | |
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299 A. The LaTeX source for the documentation is part of the source |
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300 distribution. If you don't have LaTeX, the latest Python |
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301 documentation set is always available by anonymous ftp, e.g. |
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302 <URL:ftp://ftp.python.org/pub/python/doc/postscript.tar.gz>. It is a |
| 2048 | 303 gzipped tar file containing PostScript files of the reference manual, |
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304 the library manual, and the tutorial. Note that the library manual is |
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305 the most important one of the set, as much of Python's power stems |
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306 from the standard or built-in types, functions and modules, all of |
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307 which are described here. PostScript for a high-level description of |
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308 Python is in the file nluug-paper.ps (a separate file on the ftp |
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309 site). |
| 1529 | 310 |
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311 1.5. Q. Are there other ftp sites that mirror the Python distribution? |
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312 |
| 2048 | 313 A. The following anonymous ftp sites keep mirrors of the Python |
| 314 distribution: | |
| 1529 | 315 |
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316 USA: |
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317 |
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318 <URL:ftp://ftp.python.org/pub/python/> |
| 2048 | 319 <URL:ftp://gatekeeper.dec.com/pub/plan/python/> |
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320 <URL:ftp://ftp.uu.net/languages/python/> |
| 2048 | 321 <URL:ftp://ftp.wustl.edu/graphics/graphics/sgi-stuff/python/> |
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322 <URL:ftp://ftp.sterling.com/programming/languages/python/> |
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323 <URL:ftp://uiarchive.cso.uiuc.edu/pub/lang/python/> |
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324 <URL:ftp://ftp.pht.com/mirrors/python/python/> |
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325 |
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326 Europe: |
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327 |
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328 <URL:ftp://ftp.cwi.nl/pub/python/> |
| 2048 | 329 <URL:ftp://ftp.funet.fi/pub/languages/python/> |
| 330 <URL:ftp://ftp.sunet.se/pub/lang/python/> | |
| 2855 | 331 <URL:ftp://unix.hensa.ac.uk/mirrors/uunet/languages/python/> |
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332 <URL:ftp://ftp.ibp.fr/pub/python/> |
| 2855 | 333 <URL:ftp://ftp.switch.ch/software/sources/python/> |
| 334 <URL:ftp://ftp.informatik.tu-muenchen.de/pub/comp/programming/languages/python/> | |
| 1529 | 335 |
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336 Australia: |
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337 |
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338 <URL:ftp://ftp.dstc.edu.au/pub/python/> |
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339 |
| 2048 | 340 Or try archie on the string "python". |
| 1529 | 341 |
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342 1.6. Q. Is there a newsgroup or mailing list devoted to Python? |
| 1529 | 343 |
| 2048 | 344 A. There is a newsgroup, comp.lang.python <URL:news:comp.lang.python>, |
| 345 and a mailing list. The newsgroup and mailing list are gatewayed into | |
| 346 each other -- if you can read news it's unnecessary to subscribe to | |
| 347 the mailing list. Send e-mail to <python-list-request@cwi.nl> to | |
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348 (un)subscribe to the mailing list. Hypermail archives of (nearly) |
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349 everything posted to the mailing list (and thus the newsgroup) are |
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350 available on our WWW server, |
| 2048 | 351 <URL:http://www.cwi.nl/~guido/hypermail/index.html>. The raw archives |
| 352 are also available by ftp, e.g. | |
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353 <URL:ftp://ftp.python.org/pub/python/mail/mailinglist.gz>. The |
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354 uncompressed versions of these files can be read with the standard |
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355 UNIX Mail program ("Mail -f file") or with nn ("nn file"). To read |
| 3018 | 356 them using MH, you could use "inc -file file". (The archival service |
| 357 has stopped archiving new articles around the end of April 1995. I | |
| 358 hope to revive it on the PSA server www.python.org sometime in the | |
| 359 future.) | |
| 1529 | 360 |
| 2048 | 361 1.7. Q. Is there a WWW page devoted to Python? |
| 362 | |
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363 A. Yes, <URL:http://www.python.org/> is the official Python home page. |
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364 At the time of writing, this page is not yet completely operational; |
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365 you may have a look at the old Python home page: |
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366 <URL:http://www.cwi.nl/~guido/Python.html> or at the U.S. copy: |
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367 <URL:http://www.python.org/~guido/Python.html>. |
| 2048 | 368 |
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369 1.8. Q. Is the Python documentation available on the WWW? |
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370 |
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371 A. Yes, see <URL:http://www.python.org/> (Python's home page). It |
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372 contains pointers to hypertext versions of the whole documentation set |
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373 (as hypertext, not just PostScript). |
| 1529 | 374 |
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375 If you wish to browse this collection of HTML files on your own |
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376 machine, it is available bundled up by anonymous ftp, |
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377 e.g. <URL:ftp://ftp.python.org/pub/python/doc/html.tar.gz>. |
| 1529 | 378 |
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379 An Emacs-INFO set containing the library manual is also available by |
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380 ftp, e.g. <URL:ftp://ftp.python.org/pub/python/doc/lib-info.tar.gz>. |
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381 |
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382 1.9. Q. Is there a book on Python, or will there be one out soon? |
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383 |
| 2855 | 384 A. Mark Lutz is writing a Python book for O'Reilly and Associates, to |
| 385 be published early 1996. See the outline (in PostScript): | |
| 386 <URL:http://www.python.org/workshops/1995-05/outlinep.eps>. | |
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387 |
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388 1.10. Q. Are there any published articles about Python that I can quote? |
| 1529 | 389 |
| 390 A. So far the only refereed and published article that describes | |
| 391 Python in some detail is: | |
| 392 | |
| 393 Guido van Rossum and Jelke de Boer, "Interactively Testing Remote | |
| 394 Servers Using the Python Programming Language", CWI Quarterly, Volume | |
| 395 4, Issue 4 (December 1991), Amsterdam, pp 283-303. | |
| 396 | |
| 397 LaTeX source for this paper is available as part of the Python source | |
| 398 distribution. | |
| 399 | |
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400 See also the next section (supposedly Aaron Watters' paper has been |
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401 refereed). |
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402 |
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403 1.11. Q. Are there short introductory papers or talks on Python? |
| 2048 | 404 |
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405 A. A recent, very entertaining introduction to Python is the tutorial by |
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406 Aaron Watters in UnixWorld Online: |
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407 |
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408 Aaron R. Watters: "The What, Why, Who, and Where of Python", |
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409 <URL:http://www.wcmh.com/uworld/archives/95/tutorial/005.html> |
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410 |
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411 An olded paper is: |
| 1529 | 412 |
| 413 Guido van Rossum, "An Introduction to Python for UNIX/C | |
| 414 Programmers", in the proceedings of the NLUUG najaarsconferentie | |
| 1942 | 415 1993 (dutch UNIX users group meeting November 1993). |
| 2048 | 416 |
| 1529 | 417 PostScript for this paper and for the slides used for the accompanying |
| 2048 | 418 presentation is available by ftp as |
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419 <URL:ftp://ftp.python.org/pub/python/doc/nluug-paper.ps> and |
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420 <URL:ftp://ftp.python.org/pub/python/doc/nluug-slides.ps>, respectively. |
| 1529 | 421 |
| 2048 | 422 Slides for a talk on Python that I gave at the Usenix Symposium on |
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423 Very High Level Languages in Santa Fe, NM, USA in October 1994 are |
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424 available as <URL:ftp://ftp.python.org/pub/python/doc/vhll-slides.ps>. |
| 2048 | 425 |
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426 1.12. Q. How does the Python version numbering scheme work? |
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427 |
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428 A. Python versions are numbered A.B.C or A.B. A is the major version |
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429 number -- it is only incremented for major changes in functionality or |
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430 source structure. B is the minor version number, incremented for less |
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431 earth-shattering changes to a release. C is the patchlevel -- it is |
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432 incremented for each new patch release. Not all releases have patch |
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433 releases. Note that in the past, patches have added significant |
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434 changes; in fact the changeover from 0.9.9 to 1.0.0 was the first time |
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435 that either A or B changed! |
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436 |
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437 Beta versions have an additional suffix of "betaN" for some small |
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438 number N. Note that (for instance) all versions labeled 1.4betaN |
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439 *precede* the actual release of 1.4. 1.4b3 is short for 1.4beta3. |
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440 |
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441 1.13. Q. How do I get a beta test version of Python? |
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442 |
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443 A. If there are any beta releases, they are published in the normal |
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444 source directory (e.g. <URL:ftp://ftp.python.org/pub/python/src/>). |
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445 |
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446 1.14. Q. Are there copyright restrictions on the use of Python? |
| 1663 | 447 |
| 448 A. Hardly. You can do anything you want with the source, as long as | |
| 2048 | 449 you leave the copyrights in, and display those copyrights in any |
| 450 documentation about Python that you produce. Also, don't use the | |
| 451 author's institute's name in publicity without prior written | |
| 452 permission, and don't hold them responsible for anything (read the | |
| 453 actual copyright for a precise legal wording). | |
| 454 | |
| 455 In particular, if you honor the copyright rules, it's OK to use Python | |
| 456 for commercial use, to sell copies of Python in source or binary form, | |
| 457 or to sell products that enhance Python or incorporate Python (or part | |
| 458 of it) in some form. I would still like to know about all commercial | |
| 459 use of Python! | |
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460 |
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461 1.15. Q. Why was Python created in the first place? |
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462 |
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463 A. Here's a *very* brief summary of what got me started: |
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464 |
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465 - I had extensive experience with implementing an interpreted language |
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466 in the ABC group at CWI, and from working with this group I had |
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467 learned a lot about language design. This is the origin of many |
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468 Python features, including the use of indentation for statement |
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469 grouping and the inclusion of very-high-level data types (although the |
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470 details are all different in Python). |
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471 |
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472 - I had a number of gripes about the ABC language, but also liked many |
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473 of its features. It was impossible to extend the ABC language (or its |
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474 implementation) to remedy my complaints -- in fact its lack of |
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475 extensibility was one of its biggest problems. |
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476 |
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477 - I had some experience with using Modula-2+ and talked with the |
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478 designers of Modula-3 (and read the M3 report). M3 is the origin of |
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479 the syntax and semantics used for exceptions, and some other Python |
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480 features. |
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481 |
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482 - I was working in the Amoeba distributed operating system group at |
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483 CWI. We needed a better way to do system administration than by |
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484 writing either C programs or Bourne shell scripts, since Amoeba had |
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485 its own system call interface which wasn't easily accessible from the |
| 3018 | 486 Bourne shell. My experience with error handling in Amoeba made me |
| 487 acutely aware of the importance of exceptions as a programming | |
| 488 language feature. | |
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489 |
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490 - It occurred to me that a scripting language with a syntax like ABC |
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491 but with access to the Amoeba system calls would fill the need. I |
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492 realized that it would be foolish to write an Amoeba-specific |
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493 language, so I decided that I needed a language that was generally |
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494 extensible. |
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495 |
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496 - During the 1989 Christmas holidays, I had a lot of time on my hand, |
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497 so I decided to give it a try. During the next year, while still |
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498 mostly working on it in my own time, Python was used in the Amoeba |
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499 project with increasing success, and the feedback from colleagues made |
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500 me add many early improvements. |
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501 |
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502 - In February 1991, after just over a year of development, I decided |
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503 to post to USENET. The rest is in the Misc/HISTORY file. |
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504 |
| 1529 | 505 |
| 506 2. Python in the real world | |
| 507 =========================== | |
| 508 | |
| 509 2.1. Q. How many people are using Python? | |
| 510 | |
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511 A. I don't know, but the maximum number of simultaneous subscriptions |
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512 to the Python mailing list before it was gatewayed into the newsgroup |
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513 was about 180 (several of which were local redistribution lists). I |
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514 believe that many active Python users don't bother to subscribe to the |
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515 list, and now that there's a newsgroup the mailing list subscription |
| 1663 | 516 is even less meaningful. I see new names on the newsgroup all the |
| 517 time and my best guess is that there are currently at least several | |
| 518 thousands of users. | |
| 1529 | 519 |
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520 Another statistic is the number of accesses to the Python WWW server. |
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521 Have a look at <URL:http://www.python.org/stats/>. |
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522 |
| 1529 | 523 2.2. Q. Have any significant projects been done in Python? |
| 524 | |
| 525 A. Here at CWI (the home of Python), we have written a 20,000 line | |
| 526 authoring environment for transportable hypermedia presentations, a | |
|
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527 5,000 line multimedia teleconferencing tool, as well as many many |
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528 smaller programs. |
| 1529 | 529 |
| 530 The University of Virginia uses Python to control a virtual reality | |
| 531 engine. Contact: Matt Conway <conway@virginia.edu>. | |
| 532 | |
| 2048 | 533 The ILU project at Xerox PARC can generate Python glue for ILU |
| 534 interfaces. See <URL:ftp://ftp.parc.xerox.com/pub/ilu/ilu.html>. | |
| 535 | |
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536 The University of California, Irvine uses a student administration |
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537 system called TELE-Vision written entirely in Python. Contact: Ray |
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538 Price <rlprice@uci.edu>. |
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539 |
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540 See also the next question. |
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541 |
|
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542 If you have done a significant project in Python that you'd like to be |
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543 included in the list above, send me email! |
| 1529 | 544 |
| 545 2.3. Q. Are there any commercial projects going on using Python? | |
| 546 | |
| 547 A. Several companies have revealed to me that they are planning or | |
|
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548 considering use of Python in a future product. |
|
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549 |
| 3018 | 550 Sunrise Software has a product out using Python -- they use Python |
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551 for a GUI management application and an SNMP network management |
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552 application. Contact: <info@sunrise.com>. |
| 1529 | 553 |
| 2048 | 554 Infoseek uses Python to implement their commercial WWW information |
| 555 retrieval service <URL:http://www.infoseek.com/>. Contact: | |
| 556 <info@infoseek.com>. | |
|
1784
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557 |
| 2048 | 558 Paul Everitt of Connecting Minds is planning a Lotus Notes gateway. |
| 559 Contact: <Paul.Everitt@cminds.com>. Or see their WWW server | |
| 560 <URL:http://www.cminds.com/>. | |
| 561 | |
|
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562 KaPRE in Boulder, CO is using Python for on-site customization of C++ |
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563 applications, rapid-prototyping/development, |
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564 language-based-components, and possibly more. This is pretty solid: |
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565 Python's being shipped with their tool-set now, to beta sites. |
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566 Contact: <lutz@KaPRE.COM> (Mark Lutz). |
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567 |
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568 Individuals at many other companies are using Python for internal |
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569 development or for as yet unannounced products (witness their |
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570 contributions to the Python mailing list or newsgroup). |
| 1529 | 571 |
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572 SGI has advertised in the Python list looking for Python programmers |
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573 for a project involving interactive television. |
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574 |
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575 See also the workshop minutes at |
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576 <URL:http://www.python.org/workshops/> -- in general the WWW server is |
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577 more up to date than the FAQ for these issues. |
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578 |
| 1529 | 579 Python has also been elected as an extension language by MADE, a |
| 580 consortium supported by the European Committee's ESPRIT program and | |
| 581 consisting of Bull, CWI and some other European companies. Contact: | |
| 582 Ivan Herman <ivan@cwi.nl>. | |
| 583 | |
|
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584 If you'd like to be included in the list above, send me email! |
|
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585 |
|
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586 2.4. Q. How stable is Python? |
| 1529 | 587 |
|
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588 A. Very stable. While the current version number would suggest it is |
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589 in the early stages of development, in fact new, stable releases |
|
3207
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all sorts of minor nits
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590 (numbered 0.9.x through 1.3) have been coming out roughly every 3 to |
| 2048 | 591 6 months for the past four years. |
|
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592 |
|
4250
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593 2.5. Q. What new developments are expected for Python in the future? |
| 1529 | 594 |
|
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595 A. See my Work-In-Progress web page, currently at |
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596 <URL:http://www.python.org:~guido/WIP.html>, and the pages for the |
|
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597 Second Python Workshop (best reached via the Python home page, |
|
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598 <URL:http://www.python.org/>). Also follow the newsgroup discussions! |
| 2048 | 599 |
|
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600 2.6. Q. Is it reasonable to propose incompatible changes to Python? |
|
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601 |
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602 A. In general, no. There are already millions of lines of Python code |
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603 around the world, so any changes in the language that invalidates more |
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604 than a very small fraction of existing programs has to be frowned |
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605 upon. Even if you can provide a conversion program, there still is |
|
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606 the problem of updating all documentation. Providing a gradual |
|
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607 upgrade path is the only way if a feature has to be changed. |
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608 |
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609 2.7. Q. What is the future of Python? |
| 1529 | 610 |
|
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611 A. If I knew, I'd be rich :-) |
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612 |
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613 Seriously, the formation of the PSA (Pyton Software Activity, see |
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614 <URL:http://www.python.org/psa/>) ensures some kind of support even in |
|
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615 the (unlikely! event that I'd be hit by a bus (actually, here in the |
|
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616 US, a car accident would be more likely :-), were to join a nunnery, |
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617 or would be head-hunted. A large number of Python users have become |
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618 experts at Python programming as well as maintenance of the |
|
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619 implementation, and would easily fill the vacuum created by my |
|
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620 disappearance. |
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621 |
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622 In the mean time, I have no plans to disappear -- rather, I am |
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623 committed to improving Python, and my current benefactor, CNRI (see |
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624 <URL:http://www.cnri.reston.va.us>) is just as committed to continue |
|
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625 its support of Python and the PSA. In fact, we have great plans for |
|
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626 Python -- we just can't tell yet! |
|
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627 |
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628 2.8. Q. What is the PSA, anyway? |
|
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629 |
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630 A. The Python Software Activity <URL:http://www.python.org/psa/> was |
|
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|
631 created by a number of Python aficionados who want Python to be more |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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632 than the product and responsibility of a single individual. It has |
|
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|
633 found a home at CNRI <URL:http://www.cnri.reston.va.us>. Anybody who |
|
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634 wishes Python well should join the PSA. |
|
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635 |
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636 2.9. Q. How do I join the PSA? |
|
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637 |
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638 A. The full scoop is available on the web, see |
|
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639 <URL:http://www.python.org/psa/Joining.html>. Summary: send a check |
|
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640 of at least $50 to CNRI/PSA, 1895 Preston White Drive, Suite 100, in |
|
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66913ca7ec47
New email and zip code for Guido
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641 Reston, VA 20191. Full-time students pay $25. Companies can join for |
|
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642 a mere $500. |
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643 |
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644 2.10. Q. What are the benefits of joining the PSA? |
|
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645 |
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646 A. Like National Public Radio, if not enough people join, Python will |
|
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647 wither. Your name will be mentioned on the PSA's web server. |
|
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648 Workshops organized by the PSA <URL:http://www.python.org/workshops/> |
|
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649 are only accessible to PSA members (you can join at the door). The |
|
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650 PSA is working on additional benefits, such as reduced prices for |
|
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651 books and software, and early access to beta versions of Python. |
|
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652 |
|
3023
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653 |
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654 3. Building Python and Other Known Bugs |
|
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655 ======================================= |
| 1529 | 656 |
|
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At the release of 1.0.1
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657 3.1. Q. Is there a test set? |
| 1529 | 658 |
| 659 A. Yes, simply do "import testall" (or "import autotest" if you aren't | |
| 660 interested in the output). The standard modules whose name begins | |
| 661 with "test" together comprise the test. The test set doesn't test | |
| 662 *all* features of Python but it goes a long way to confirm that a new | |
| 663 port is actually working. The Makefile contains an entry "make test" | |
| 2048 | 664 which runs the autotest module. NOTE: if "make test" fails, run the |
| 665 tests manually ("import testall") to see what goes wrong before | |
| 666 reporting the error. | |
| 1529 | 667 |
|
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At the release of 1.0.1
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|
668 3.2. Q. When running the test set, I get complaints about floating point |
| 1529 | 669 operations, but when playing with floating point operations I cannot |
| 670 find anything wrong with them. | |
| 671 | |
| 672 A. The test set makes occasional unwarranted assumptions about the | |
| 673 semantics of C floating point operations. Until someone donates a | |
| 674 better floating point test set, you will have to comment out the | |
| 675 offending floating point tests and execute similar tests manually. | |
| 676 | |
|
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677 3.3. Q. Link errors after rerunning the configure script. |
|
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678 |
|
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Released version 1.4; out after 1.0.0 is released...
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679 A. It is generally necessary to run "make clean" after a configuration |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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680 change. |
|
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681 |
|
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next version; python.org changes
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|
682 3.4. Q. The python interpreter complains about options passed to a |
|
1541
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Released version 1.4; out after 1.0.0 is released...
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683 script (after the script name). |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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684 |
|
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|
685 A. You are probably linking with GNU getopt, e.g. through -liberty. |
|
1784
a3f199e8bac6
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|
686 Don't. The reason for the complaint is that GNU getopt, unlike System |
|
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1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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|
687 V getopt and other getopt implementations, doesn't consider a |
|
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1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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|
688 non-option to be the end of the option list. A quick (and compatible) |
|
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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parents:
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|
689 fix for scripts is to add "--" to the interpreter, like this: |
|
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|
690 |
| 2048 | 691 #! /usr/local/bin/python -- |
|
1784
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1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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|
692 |
|
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1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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|
693 You can also use this interactively: |
|
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|
694 |
| 2048 | 695 python -- script.py [options] |
| 696 | |
| 697 Note that a working getopt implementation is provided in the Python | |
| 698 distribution (in Python/getopt.c) but not automatically used. | |
|
1541
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Released version 1.4; out after 1.0.0 is released...
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|
699 |
|
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next version; python.org changes
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|
700 3.5. Q. When building on the SGI, make tries to run python to create |
|
1541
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Released version 1.4; out after 1.0.0 is released...
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|
701 glmodule.c, but python hasn't been built or installed yet. |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
702 |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
703 A. Comment out the line mentioning glmodule.c in Setup and build a |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
704 python without gl first; install it or make sure it is in your $PATH, |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
705 then edit the Setup file again to turn on the gl module, and make |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
706 again. You don't need to do "make clean"; you do need to run "make |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
707 Makefile" in the Modules subdirectory (or just run "make" at the |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
708 toplevel). |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
709 |
|
4250
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Removed some obsolete questions and references to version 1.2.
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|
710 3.6. Q. I use VPATH but some targets are built in the source directory. |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
711 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
712 A. On some systems (e.g. Sun), if the target already exists in the |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
713 source directory, it is created there instead of in the build |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
714 directory. This is usually because you have previously built without |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
715 VPATH. Try running "make clobber" in the source directory. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
716 |
|
4250
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Removed some obsolete questions and references to version 1.2.
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|
717 3.7. Q. Trouble building or linking with the GNU readline library. |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
718 |
|
2660
4eb6ddb9e961
Some more changes for 1.2
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
719 A. Consider using readline 2.0. Some hints: |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
720 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
721 - You can use the GNU readline library to improve the interactive user |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
722 interface: this gives you line editing and command history when |
|
2208
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
723 calling python interactively. You need to configure and build the GNU |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
724 readline library before running the configure script. Its sources are |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
725 no longer distributed with Python; you can ftp them from any GNU |
| 2048 | 726 mirror site, or from its home site |
| 727 <URL:ftp://slc2.ins.cwru.edu/pub/dist/readline-2.0.tar.gz> (or a | |
| 728 higher version number -- using version 1.x is not recommended). Pass | |
| 729 the Python configure script the option --with-readline=DIRECTORY where | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
730 DIRECTORY is the absolute pathname of the directory where you've built |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
731 the readline library. Some hints on building and using the readline |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
732 library: |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
733 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
734 - On SGI IRIX 5, you may have to add the following |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
735 to rldefs.h: |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
736 |
| 2048 | 737 #ifndef sigmask |
| 738 #define sigmask(sig) (1L << ((sig)-1)) | |
| 739 #endif | |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
740 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
741 - On most systems, you will have to add #include "rldefs.h" to the |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
742 top of several source files, and if you use the VPATH feature, you |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
743 will have to add dependencies of the form foo.o: foo.c to the |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
744 Makefile for several values of foo. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
745 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
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|
746 - The readline library requires use of the termcap library. A |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
747 known problem with this is that it contains entry points which |
| 1942 | 748 cause conflicts with the STDWIN and SGI GL libraries. The STDWIN |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
749 conflict can be solved (and will be, in the next release of |
| 1942 | 750 STDWIN) by adding a line saying '#define werase w_erase' to the |
| 751 stdwin.h file (in the STDWIN distribution, subdirectory H). The | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
752 GL conflict has been solved in the Python configure script by a |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
753 hack that forces use of the static version of the termcap library. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
754 |
|
2660
4eb6ddb9e961
Some more changes for 1.2
Guido van Rossum <guido@python.org>
parents:
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changeset
|
755 - Check the newsgroup gnu.bash.bug <URL:news:gnu.bash.bug> for |
|
4eb6ddb9e961
Some more changes for 1.2
Guido van Rossum <guido@python.org>
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changeset
|
756 specific problems with the readline library (I don't read this group |
|
4eb6ddb9e961
Some more changes for 1.2
Guido van Rossum <guido@python.org>
parents:
2526
diff
changeset
|
757 but I've been told that it is the place for readline bugs). |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
1902
diff
changeset
|
758 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
759 3.8. Q. Trouble with socket I/O on older Linux 1.x versions. |
|
3727
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
760 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
761 A. Once you've built Python, use it to run the regen.py script in the |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
762 Lib/linux1 directory. Apparently the files as distributed don't match |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
763 the system headers on some Linux versions. |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
764 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
765 3.9. Q. Trouble with prototypes on Ultrix. |
|
1957
38dcb090f48b
add warning about ultrix cc
Guido van Rossum <guido@python.org>
parents:
1942
diff
changeset
|
766 |
|
38dcb090f48b
add warning about ultrix cc
Guido van Rossum <guido@python.org>
parents:
1942
diff
changeset
|
767 A. Ultrix cc seems broken -- use gcc, or edit config.h to #undef |
|
38dcb090f48b
add warning about ultrix cc
Guido van Rossum <guido@python.org>
parents:
1942
diff
changeset
|
768 HAVE_PROTOTYPES. |
|
38dcb090f48b
add warning about ultrix cc
Guido van Rossum <guido@python.org>
parents:
1942
diff
changeset
|
769 |
|
4376
d4f64fc42d84
Toss Q 3.10 on posix.listdir on NeXT. Add revived vpApp.
Guido van Rossum <guido@python.org>
parents:
4278
diff
changeset
|
770 3.10. Q. Other trouble building Python on platform X. |
|
1533
995a8ef4a5c0
Changes for release of 1.0.0
Guido van Rossum <guido@python.org>
parents:
1529
diff
changeset
|
771 |
|
4221
66913ca7ec47
New email and zip code for Guido
Guido van Rossum <guido@python.org>
parents:
3865
diff
changeset
|
772 A. Please email the details to <guido@cnri.reston.va.us> and I'll look |
|
66913ca7ec47
New email and zip code for Guido
Guido van Rossum <guido@python.org>
parents:
3865
diff
changeset
|
773 into it. Please provide as many details as possible. In particular, |
|
66913ca7ec47
New email and zip code for Guido
Guido van Rossum <guido@python.org>
parents:
3865
diff
changeset
|
774 if you don't tell me what type of computer and what operating system |
|
66913ca7ec47
New email and zip code for Guido
Guido van Rossum <guido@python.org>
parents:
3865
diff
changeset
|
775 (and version) you are using it will be difficult for me to figure out |
|
66913ca7ec47
New email and zip code for Guido
Guido van Rossum <guido@python.org>
parents:
3865
diff
changeset
|
776 what is the matter. If you get a specific error message, please email |
|
66913ca7ec47
New email and zip code for Guido
Guido van Rossum <guido@python.org>
parents:
3865
diff
changeset
|
777 it to me too. |
| 1529 | 778 |
|
4376
d4f64fc42d84
Toss Q 3.10 on posix.listdir on NeXT. Add revived vpApp.
Guido van Rossum <guido@python.org>
parents:
4278
diff
changeset
|
779 3.11. Q. How to configure dynamic loading on Linux. |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
780 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
781 A. This is now automatic as long as your Linux version uses the ELF |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
782 object format (all recent Linuxes do). |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
783 |
|
4408
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
784 3.12. Q: I can't get shared modules to work on Linux 2.0 (Slackware96)? |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
785 |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
786 A: This is a bug in the Slackware96 release. The fix is simple: |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
787 |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
788 Make sure that there is a link from /lib/libdl.so to /lib/libdl.so.1 |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
789 so that the following links are setup: |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
790 |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
791 /lib/libdl.so -> /lib/libdl.so.1 |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
792 /lib/libdl.so.1 -> /lib/libdl.so.1.7.14 |
|
6c771ea38eee
Added item about bug in Slackware96 libdl.
Guido van Rossum <guido@python.org>
parents:
4376
diff
changeset
|
793 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
794 3.13. Q: Trouble when making modules shared on Linux. |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
795 |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
796 A. This happens when you have built Python for static linking and then |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
797 enable *shared* in the Setup file. Shared library code must be |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
798 compiled with "-fpic". If a .o file for the module already exist that |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
799 was compiled for static linking, you must remove it or do "make clean" |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
800 in the Modules directory. |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
801 |
|
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
802 3.14. Q. How to use threads on Linux. |
|
4480
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
803 |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
804 A. [Greg Stein] I built myself a libpthreads.so from the libc.5.3.12 |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
805 distribution (the binary distribution doesn't have pthreads in |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
806 it). Then, I configured Python with --with-threads and then tweaked |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
807 config.h to include a #define _MIT_POSIX_THREADS (or something like |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
808 that, see /usr/include/pthreads.h). It worked fine at that point. |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
809 |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
810 Note that I couldn't get threading to "operate well" with any of the |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
811 other thread packages. Prior libc versions didn't integrate well with |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
812 threads, either, so I couldn't use them (e.g. sleep() blocked all |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
813 threads :-( ). |
|
9e853a5f04ff
Added answer by Greg Stein about threads on Linux.
Guido van Rossum <guido@python.org>
parents:
4438
diff
changeset
|
814 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
815 3.15. Q. Errors when linking with a shared library containing C++ code. |
| 2855 | 816 |
| 817 A. Link the main Python binary with C++. Change the definition of | |
| 818 LINKCC in Modules/Makefile to be your C++ compiler. You may have to | |
| 819 edit config.c slightly to make it compilable with C++. | |
| 2301 | 820 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
821 3.16. Q. I built with tkintermodule.c enabled but get "Tkinter not found". |
|
3023
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
822 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
823 A. Tkinter.py (note: upper case T) lives in a subdirectory of Lib, |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
824 Lib/tkinter. If you are using the default module search path, you |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
825 probably didn't enable the line in the Modules/Setup file defining |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
826 TKPATH; if you use the environment variable PYTHONPATH, you'll have to |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
827 add the proper tkinter subdirectory. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
828 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
829 3.17. Q. I built with Tk 4.0 but Tkinter complains about the Tk version. |
|
3023
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
830 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
831 A. Several things could cause this. You most likely have a Tk 3.6 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
832 installation that wasn't completely eradicated by the Tk 4.0 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
833 installation (which tends to add "4.0" to its installed files). You |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
834 may have the Tk 3.6 support library installed in the place where the |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
835 Tk 4.0 support files should be (default /usr/local/lib/tk/); you may |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
836 have compiled Python with the old tk.h header file (yes, this actually |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
837 compiles!); you may actually have linked with Tk 3.6 even though Tk |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
838 4.0 is also around. Similar for Tcl 7.4 vs. Tcl 7.3. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
839 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
840 3.18. Q. Link errors for Tcl/Tk symbols when linking with Tcl/Tk. |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
841 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
842 Quite possibly, there's a version mismatch between the Tcl/Tk header |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
843 files (tcl.h and tk.h) and the tck/tk libraries you are using (the |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
844 "-ltk4.0" and "-ltcl7.4" arguments for _tkinter in the Setup file). |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
845 If you have installed both versions 7.4/4.0 and 7.5/4.1 of Tcl/Tk, |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
846 most likely your header files are for The newer versions, but the |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
847 Setup line for _tkinter in some Python distributions references |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
848 7.4/4.0 by default. Changing this to 7.5/4.1 should take care of |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
849 this. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
850 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
851 3.19. Q. I configured and built Python for Tcl/Tk but "import Tkinter" |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
852 fails. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
853 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
854 A. Most likely, you forgot to enable the line in Setup that says |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
855 "TKPATH=:$(DESTLIB)/tkinter". |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
856 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
857 3.20. Q. Tk doesn't work right on DEC Alpha. |
|
3023
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
858 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
859 A. You probably compiled either Tcl, Tk or Python with gcc. Don't. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
860 For this platform, which has 64-bit integers, gcc is known to generate |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
861 broken code. The standard cc (which comes bundled with the OS!) |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
862 works. If you still prefer gcc, at least try recompiling with cc |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
863 before reporting problems to the newsgroup or the author; if this |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
864 fixes the problem, report the bug to the gcc developers instead. (As |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
865 far as we know, there are no problem with gcc on other platforms -- |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
866 the instabilities seem to be restricted to the DEC Alpha.) See also |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
867 question 3.6. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
868 |
|
4542
652303ef926b
Added Q. about enabling *shared* on Linux.
Guido van Rossum <guido@python.org>
parents:
4480
diff
changeset
|
869 3.21. Q. Several common system calls are missing from the posix module. |
|
3727
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
870 |
|
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871 A. Most likely, *all* test compilations run by the configure script |
|
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872 are failing for some reason or another. Have a look in config.log to |
|
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873 see what could be the reason. A common reason is specifying a |
|
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874 directory to the --with-readline option that doesn't contain the |
|
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875 libreadline.a file. |
|
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876 |
|
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877 3.22. Q. ImportError: No module named string, on MS Windows. |
|
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878 |
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879 A. Most likely, your PYTHONPATH environment variable should be set to |
|
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880 something like: |
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881 |
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882 set PYTHONPATH=c:\python;c:\python\lib;c:\python\scripts |
|
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883 |
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884 (assuming Python was installed in c:\python) |
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885 |
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886 3.23. Q. Core dump on SGI when using the gl module. |
|
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887 |
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888 There are conflicts between entry points in the termcap and curses |
|
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889 libraries and an entry point in the GL library. There's a hack of a |
|
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890 fix for the termcap library if it's needed for the GNU readline |
|
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891 library, but it doesn't work when you're using curses. Concluding, |
|
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892 you can't build a Python binary containing both the curses and gl |
|
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893 modules. |
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894 |
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895 |
| 1529 | 896 |
| 897 4. Programming in Python | |
| 898 ======================== | |
| 899 | |
|
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900 4.1. Q. Is there a source code level debugger with breakpoints, step, |
|
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901 etc.? |
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902 |
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903 A. Yes. Check out module pdb; pdb.help() prints the documentation (or |
|
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904 you can read it as Lib/pdb.doc). If you use the STDWIN option, |
|
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905 there's also a windowing interface, wdb. You can write your own |
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906 debugger by using the code for pdb or wdb as an example. |
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907 |
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908 4.2. Q. Can I create an object class with some methods implemented in |
| 1529 | 909 C and others in Python (e.g. through inheritance)? (Also phrased as: |
| 910 Can I use a built-in type as base class?) | |
| 911 | |
| 912 A. No, but you can easily create a Python class which serves as a | |
| 913 wrapper around a built-in object, e.g. (for dictionaries): | |
| 914 | |
| 2048 | 915 # A user-defined class behaving almost identical |
| 916 # to a built-in dictionary. | |
| 917 class UserDict: | |
| 918 def __init__(self): self.data = {} | |
| 919 def __repr__(self): return repr(self.data) | |
| 920 def __cmp__(self, dict): | |
| 921 if type(dict) == type(self.data): | |
| 922 return cmp(self.data, dict) | |
| 923 else: | |
| 924 return cmp(self.data, dict.data) | |
| 925 def __len__(self): return len(self.data) | |
| 926 def __getitem__(self, key): return self.data[key] | |
| 927 def __setitem__(self, key, item): self.data[key] = item | |
| 928 def __delitem__(self, key): del self.data[key] | |
| 929 def keys(self): return self.data.keys() | |
| 930 def items(self): return self.data.items() | |
| 931 def values(self): return self.data.values() | |
| 932 def has_key(self, key): return self.data.has_key(key) | |
| 1529 | 933 |
|
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934 4.3. Q. Is there a curses/termcap package for Python? |
| 1529 | 935 |
| 2048 | 936 A. Yes -- Lance Ellinghaus has written a module that interfaces to |
|
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937 System V's "ncurses". If you know a little curses and some Python, |
| 2048 | 938 it's straightforward to use. It is part of the standard Python |
| 939 distribution, but not configured by default -- you must enable it by | |
| 940 editing Modules/Setup. It requires a System V curses implementation. | |
|
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941 |
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|
942 You could also consider using the "alfa" (== character cell) version |
| 2048 | 943 of STDWIN. (Standard Window System Interface, a portable windowing |
| 944 system interface by myself <URL:ftp://ftp.cwi.nl/pub/stdwin/>.) This | |
|
1903
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945 will also prepare your program for porting to windowing environments |
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|
946 such as X11 or the Macintosh. |
| 1529 | 947 |
|
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948 4.4. Q. Is there an equivalent to C's onexit() in Python? |
| 1529 | 949 |
| 950 A. Yes, if you import sys and assign a function to sys.exitfunc, it | |
| 951 will be called when your program exits, is killed by an unhandled | |
| 952 exception, or (on UNIX) receives a SIGHUP or SIGTERM signal. | |
| 953 | |
|
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|
954 4.5. Q. When I define a function nested inside another function, the |
| 1529 | 955 nested function seemingly can't access the local variables of the |
| 956 outer function. What is going on? How do I pass local data to a | |
| 957 nested function? | |
| 958 | |
| 959 A. Python does not have arbitrarily nested scopes. When you need to | |
| 960 create a function that needs to access some data which you have | |
| 961 available locally, create a new class to hold the data and return a | |
| 962 method of an instance of that class, e.g.: | |
| 963 | |
| 2048 | 964 class MultiplierClass: |
| 965 def __init__(self, factor): | |
| 966 self.factor = factor | |
| 967 def multiplier(self, argument): | |
| 968 return argument * self.factor | |
| 969 | |
| 970 def generate_multiplier(factor): | |
| 971 return MultiplierClass(factor).multiplier | |
| 1529 | 972 |
| 2048 | 973 twice = generate_multiplier(2) |
| 974 print twice(10) | |
| 975 # Output: 20 | |
| 976 | |
| 977 An alternative solution uses default arguments, e.g.: | |
| 1529 | 978 |
| 2048 | 979 def generate_multiplier(factor): |
| 980 def multiplier(arg, fact = factor): | |
| 981 return arg*fact | |
| 982 return multiplier | |
| 983 | |
| 984 twice = generate_multiplier(2) | |
| 985 print twice(10) | |
| 986 # Output: 20 | |
| 1529 | 987 |
|
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988 4.6. Q. How do I iterate over a sequence in reverse order? |
| 1529 | 989 |
| 990 A. If it is a list, the fastest solution is | |
| 991 | |
| 2048 | 992 list.reverse() |
| 993 try: | |
| 994 for x in list: | |
| 995 "do something with x" | |
| 996 finally: | |
| 997 list.reverse() | |
| 1529 | 998 |
| 999 This has the disadvantage that while you are in the loop, the list | |
| 1000 is temporarily reversed. If you don't like this, you can make a copy. | |
| 1001 This appears expensive but is actually faster than other solutions: | |
| 1002 | |
| 2048 | 1003 rev = list[:] |
| 1004 rev.reverse() | |
| 1005 for x in rev: | |
| 1006 <do something with x> | |
| 1529 | 1007 |
| 1008 If it isn't a list, a more general but slower solution is: | |
| 1009 | |
| 2048 | 1010 i = len(list) |
| 1011 while i > 0: | |
| 1012 i = i-1 | |
| 1013 x = list[i] | |
| 1014 <do something with x> | |
| 1529 | 1015 |
| 1016 A more elegant solution, is to define a class which acts as a sequence | |
| 1017 and yields the elements in reverse order (solution due to Steve | |
| 1018 Majewski): | |
| 1019 | |
| 2048 | 1020 class Rev: |
| 1021 def __init__(self, seq): | |
| 1022 self.forw = seq | |
| 1023 def __len__(self): | |
| 1024 return len(self.forw) | |
| 1025 def __getitem__(self, i): | |
| 1026 return self.forw[-(i + 1)] | |
| 1529 | 1027 |
| 1028 You can now simply write: | |
| 1029 | |
| 2048 | 1030 for x in Rev(list): |
| 1031 <do something with x> | |
| 1529 | 1032 |
| 1942 | 1033 Unfortunately, this solution is slowest of all, due to the method |
| 1529 | 1034 call overhead... |
| 1035 | |
|
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|
1036 4.7. Q. My program is too slow. How do I speed it up? |
| 1529 | 1037 |
| 1038 A. That's a tough one, in general. There are many tricks to speed up | |
| 1039 Python code; I would consider rewriting parts in C only as a last | |
| 1040 resort. One thing to notice is that function and (especially) method | |
| 1041 calls are rather expensive; if you have designed a purely OO interface | |
| 1042 with lots of tiny functions that don't do much more than get or set an | |
| 1043 instance variable or call another method, you may consider using a | |
| 1044 more direct way, e.g. directly accessing instance variables. Also see | |
| 1045 the standard module "profile" (described in the file | |
| 1046 "python/lib/profile.doc") which makes it possible to find out where | |
| 1047 your program is spending most of its time (if you have some patience | |
| 1048 -- the profiling itself can slow your program down by an order of | |
| 1049 magnitude). | |
| 1050 | |
|
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1051 4.8. Q. When I have imported a module, then edit it, and import it |
| 1529 | 1052 again (into the same Python process), the changes don't seem to take |
| 1053 place. What is going on? | |
| 1054 | |
| 2048 | 1055 A. For reasons of efficiency as well as consistency, Python only reads |
|
2208
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1056 the module file on the first time a module is imported. (Otherwise a |
| 2048 | 1057 program consisting of many modules, each of which imports the same |
|
2208
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1058 basic module, would read the basic module over and over again.) To |
|
c68a0113b75a
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|
1059 force rereading of a changed module, do this: |
| 1529 | 1060 |
| 2048 | 1061 import modname |
| 1062 reload(modname) | |
| 1529 | 1063 |
| 1064 Warning: this technique is not 100% fool-proof. In particular, | |
| 1065 modules containing statements like | |
| 1066 | |
| 2048 | 1067 from modname import some_objects |
| 1529 | 1068 |
|
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1069 will continue to work with the old version of the imported objects. |
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1070 |
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1071 4.9. Q. How do I find the current module name? |
| 1529 | 1072 |
| 1942 | 1073 A. A module can find out its own module name by looking at the |
|
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|
1074 (predefined) global variable __name__. If this has the value |
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1075 '__main__' you are running as a script. |
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1076 |
| 2048 | 1077 4.10. Q. I have a module in which I want to execute some extra code |
| 1078 when it is run as a script. How do I find out whether I am running as | |
| 1079 a script? | |
|
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1080 |
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1081 A. See the previous question. E.g. if you put the following on the |
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1082 last line of your module, main() is called only when your module is |
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1083 running as a script: |
|
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1084 |
| 2048 | 1085 if __name__ == '__main__': main() |
|
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1086 |
| 2048 | 1087 4.11. Q. I try to run a program from the Demo directory but it fails |
| 1088 with ImportError: No module named ...; what gives? | |
| 1663 | 1089 |
| 1942 | 1090 A. This is probably an optional module (written in C!) which hasn't |
| 1091 been configured on your system. This especially happens with modules | |
| 2048 | 1092 like "Tkinter", "stdwin", "gl", "Xt" or "Xm". For Tkinter, STDWIN and |
| 1093 many other modules, see Modules/Setup.in for info on how to add these | |
| 1094 modules to your Python, if it is possible at all. Sometimes you will | |
| 1095 have to ftp and build another package first (e.g. STDWIN). Sometimes | |
| 1096 the module only works on specific platforms (e.g. gl only works on SGI | |
| 1097 machines). | |
| 1098 | |
| 1099 NOTE: if the complaint is about "Tkinter" (upper case T) and you have | |
|
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1100 already configured module "tkinter" (lower case t), the solution is |
|
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1101 *not* to rename tkinter to Tkinter or vice versa. There is probably |
|
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1102 something wrong with your module search path. Check out the value of |
|
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1103 sys.path. |
| 1663 | 1104 |
| 1942 | 1105 For X-related modules (Xt and Xm) you will have to do more work: they |
| 1106 are currently not part of the standard Python distribution. You will | |
| 2048 | 1107 have to ftp the Extensions tar file, e.g. |
|
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1108 <URL:ftp://ftp.python.org/pub/python/src/extensions.tar.gz> and follow |
|
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|
1109 the instructions there. |
| 1942 | 1110 |
| 1111 See also the next question. | |
| 1112 | |
| 1113 4.12. Q. I have successfully built Python with STDWIN but it can't | |
| 1114 find some modules (e.g. stdwinevents). | |
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1115 |
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1116 A. There's a subdirectory of the library directory named 'stdwin' |
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1117 which should be in the default module search path. There's a line in |
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1118 Modules/Setup(.in) that you have to enable for this purpose -- |
| 1942 | 1119 unfortunately in the latest release it's not near the other |
|
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1120 STDWIN-related lines so it's easy to miss it. |
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1121 |
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1122 4.13. Q. What GUI toolkits exist for Python? |
| 1663 | 1123 |
| 1124 A. Depending on what platform(s) you are aiming at, there are several. | |
| 1125 | |
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1126 Currently supported solutions: |
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1127 |
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1128 - There's a neat object-oriented interface to the Tcl/Tk widget set, |
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1129 called Tkinter. It is part of the standard Python distribution and |
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1130 well-supported -- all you need to do is build and install Tcl/Tk and |
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1131 enable the _tkinter module and the TKPATH definition in Modules/Setup |
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1132 when building Python. This is probably the easiest to install and |
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1133 use, and the most complete widget set. It is also very likely that in |
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1134 the future the standard Python GUI API will be based on or at least |
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1135 look very much like the Tkinter interface. For more info about Tk, |
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1136 including pointers to the source, see the Tcl/Tk home page |
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1137 <URL:http://www.sunlabs.com/research/tcl/>. Tcl/Tk is now fully |
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1138 portable to the Mac and Windows platforms (NT and 95 only); you need |
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1139 Python 1.4beta3 or later and Tk 4.1patch1 or later. |
| 1663 | 1140 |
| 1141 - There's an interface to X11, including the Athena and Motif widget | |
| 1142 sets (and a few individual widgets, like Mosaic's HTML widget and | |
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1143 SGI's GL widget) available from |
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1144 <URL:ftp://ftp.python.org/pub/python/src/X-extension.tar.gz>. |
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1145 Support by Sjoerd Mullender <sjoerd@cwi.nl>. |
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1146 |
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1147 - On top of the X11 interface there's the (recently revived) vpApp |
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1148 toolkit by Per Spilling, now also maintained by Sjoerd Mullender |
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1149 <sjoerd@cwi.nl>. See <URL:ftp://ftp.cwi.nl/pub/sjoerd/vpApp.tar.gz>. |
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1150 |
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1151 - The Mac port has a rich and ever-growing set of modules that support |
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1152 the native Mac toolbox calls. See the documentation that comes with |
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1153 the Mac port. See <URL:ftp://ftp.python.org/pub/python/mac>. Support |
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1154 by Jack Jansen <jack@cwi.nl>. |
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1155 |
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1156 - The NT port supported by Mark Hammond <MHammond@skippinet.com.au> |
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1157 (see question 7.2) includes an interface to the Microsoft Foundation |
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1158 Classes and a Python programming environment using it that's written |
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1159 mostly in Python. See |
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1160 <URL:ftp://ftp.python.org/pub/python/pythonwin/>. |
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1161 |
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1162 - There's an object-oriented GUI based on the Microsoft Foundation |
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1163 Classes model called WPY, supported by Jim Ahlstrom <jim@interet.com>. |
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1164 Programs written in WPY run unchanged and with native look and feel on |
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1165 Windows NT/95, Windows 3.1 (using win32s), and on Unix (using Tk). |
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1166 Source and binaries for Windows and Linux are available in |
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1167 <URL:ftp://ftp.python.org/pub/python/wpy/>. |
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1168 |
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1169 Obsolete or minority solutions: |
| 3018 | 1170 |
|
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1171 - There's an interface to wxWindows. wxWindows is a portable GUI |
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1172 class library written in C++. It supports XView, Motif, MS-Windows as |
|
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1173 targets. There is some support for Macs and CURSES as well. |
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1174 wxWindows preserves the look and feel of the underlying graphics |
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1175 toolkit. See the wxPython WWW page at |
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1176 <URL:http://www.aiai.ed.ac.uk/~jacs/wx/wxpython/wxpython.html>. |
|
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1177 Support for wxPython (by Harri Pasanen <pa@tekla.fi>) appears |
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1178 to have a low priority. |
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1179 |
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1180 - For SGI IRIX only, there are unsupported interfaces to the complete |
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1181 GL (Graphics Library -- low level but very good 3D capabilities) as |
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1182 well as to FORMS (a buttons-and-sliders-etc package built on top of GL |
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1183 by Mark Overmars -- ftp'able from |
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1184 <URL:ftp://ftp.cs.ruu.nl/pub/SGI/FORMS/>). This is probably also |
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1185 becoming obsolete, as OpenGL takes over. |
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1186 |
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1187 - There's an interface to STDWIN, a platform-independent low-level |
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1188 windowing interface for Mac and X11. This is totally unsupported and |
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1189 rapidly becoming obsolete. The STDWIN sources are at |
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1190 <URL:ftp://ftp.cwi.nl/pub/stdwin/>. (For info about STDWIN 2.0, |
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1191 please refer to Steven Pemberton <steven@cwi.nl> -- I believe it is |
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1192 also dead.) |
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1193 |
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1194 - There once was an interface to WAFE, a Tcl interface to the X11 |
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1195 Motif and Athena widget sets. WAFE is at |
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1196 <URL:ftp://ftp.wu-wien.ac.at/pub/src/X11/wafe/>. It's not clear what |
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1197 the status of the Python support is. |
| 2855 | 1198 |
|
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1199 - (The Fresco port that was mentioned in earlier versions of this FAQ |
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1200 no longer seems to exist. Inquire with Mark Linton.) |
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1201 |
| 1942 | 1202 4.14. Q. Are there any interfaces to database packages in Python? |
| 1663 | 1203 |
|
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1204 A. There's a whole collection of them in the contrib area of the ftp |
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1205 server, see <URL:http://www.python.org/ftp/python/contrib/Database/>. |
|
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c68a0113b75a
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1206 |
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1207 4.15. Q. Is it possible to write obfuscated one-liners in Python? |
|
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1208 |
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1209 A. Yes. See the following three examples, due to Ulf Bartelt: |
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1210 |
| 2048 | 1211 # Primes < 1000 |
| 1212 print filter(None,map(lambda y:y*reduce(lambda x,y:x*y!=0, | |
| 1213 map(lambda x,y=y:y%x,range(2,int(pow(y,0.5)+1))),1),range(2,1000))) | |
|
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1214 |
| 2048 | 1215 # First 10 Fibonacci numbers |
| 1216 print map(lambda x,f=lambda x,f:(x<=1) or (f(x-1,f)+f(x-2,f)): f(x,f), | |
| 1217 range(10)) | |
|
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1218 |
| 2048 | 1219 # Mandelbrot set |
| 1220 print (lambda Ru,Ro,Iu,Io,IM,Sx,Sy:reduce(lambda x,y:x+y,map(lambda y, | |
| 1221 Iu=Iu,Io=Io,Ru=Ru,Ro=Ro,Sy=Sy,L=lambda yc,Iu=Iu,Io=Io,Ru=Ru,Ro=Ro,i=IM, | |
| 1222 Sx=Sx,Sy=Sy:reduce(lambda x,y:x+y,map(lambda x,xc=Ru,yc=yc,Ru=Ru,Ro=Ro, | |
| 1223 i=i,Sx=Sx,F=lambda xc,yc,x,y,k,f=lambda xc,yc,x,y,k,f:(k<=0)or (x*x+y*y | |
| 1224 >=4.0) or 1+f(xc,yc,x*x-y*y+xc,2.0*x*y+yc,k-1,f):f(xc,yc,x,y,k,f):chr( | |
| 1225 64+F(Ru+x*(Ro-Ru)/Sx,yc,0,0,i)),range(Sx))):L(Iu+y*(Io-Iu)/Sy),range(Sy | |
| 1226 ))))(-2.1, 0.7, -1.2, 1.2, 30, 80, 24) | |
| 1227 # \___ ___/ \___ ___/ | | |__ lines on screen | |
| 1228 # V V | |______ columns on screen | |
| 1229 # | | |__________ maximum of "iterations" | |
| 1230 # | |_________________ range on y axis | |
| 1231 # |____________________________ range on x axis | |
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1232 |
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1233 Don't try this at home, kids! |
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1234 |
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1235 4.16. Q. Is there an equivalent of C's "?:" ternary operator? |
|
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1236 |
|
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1237 A. Not directly. In many cases you can mimic a?b:c with "a and b or |
|
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1238 c", but there's a flaw: if b is zero (or empty, or None -- anything |
|
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1239 that tests false) then c will be selected instead. In many cases you |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1240 can prove by looking at the code that this can't happen (e.g. because |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1241 b is a constant or has a type that can never be false), but in general |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1242 this can be a problem. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1243 |
|
4278
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
1244 Tim Peters (who wishes it was Steve Majewski) suggested the following |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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1245 solution: (a and [b] or [c])[0]. Because [b] is a singleton list it |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1246 is never false, so the wrong path is never taken; then applying [0] to |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1247 the whole thing gets the b or c that you really wanted. Ugly, but it |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1248 gets you there in the rare cases where it is really inconvenient to |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1249 rewrite your code using 'if'. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1250 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1251 4.17. Q. My class defines __del__ but it is not called when I delete the |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1252 object. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1253 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1254 A. There are several possible reasons for this. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1255 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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1256 - The del statement does not necessarily call __del__ -- it simply |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1257 decrements the object's reference count, and if this reaches zero |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1258 __del__ is called. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1259 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1260 - If your data structures contain circular links (e.g. a tree where |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1261 each child has a parent pointer and each parent has a list of |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1262 children) the reference counts will never go back to zero. You'll |
| 1942 | 1263 have to define an explicit close() method which removes those |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1264 pointers. Please don't ever call __del__ directly -- __del__ should |
| 1942 | 1265 call close() and close() should make sure that it can be called more |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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1266 than once for the same object. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1267 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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1268 - If the object has ever been a local variable (or argument, which is |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1269 really the same thing) to a function that caught an expression in an |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1270 except clause, chances are that a reference to the object still exists |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1271 in that function's stack frame as contained in the stack trace. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1272 Normally, deleting (better: assigning None to) sys.exc_traceback will |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1273 take care of this. If you a stack was printed for an unhandled |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1274 exception in an interactive interpreter, delete sys.last_traceback |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1275 instead. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1276 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1277 - There is code that deletes all objects when the interpreter exits, |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1278 but if your Python has been configured to support threads, it is not |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1279 called (because other threads may still be active). You can define |
| 1942 | 1280 your own cleanup function using sys.exitfunc (see question 4.4). |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1281 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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|
1282 - Finally, if your __del__ method raises an exception, this will be |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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|
1283 ignored. Starting with Python 1.4beta3, a warning message is printed |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
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|
1284 to sys.stderr when this happens. |
| 2048 | 1285 |
| 1286 4.18. Q. How do I change the shell environment for programs called | |
| 1287 using os.popen() or os.system()? Changing os.environ doesn't work. | |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1288 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1289 A. Modifying the environment passed to subshells was left out of the |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1290 interpreter because there seemed to be no well-established portable |
| 2048 | 1291 way to do it (in particular, some systems, have putenv(), others have |
| 1292 setenv(), and some have none at all). | |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1293 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1294 However if all you want is to pass environment variables to the |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1295 commands run by os.system() or os.popen(), there's a simple solution: |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1296 prefix the command string with a couple of variable assignments and |
|
2208
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
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|
1297 export statements. The following would be universal for popen: |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1298 |
| 2048 | 1299 import os |
| 1300 from commands import mkarg # nifty routine to add shell quoting | |
| 1301 def epopen(cmd, mode, env = {}): | |
| 1302 # env is a dictionary of environment variables | |
| 1303 prefix = '' | |
|
2208
c68a0113b75a
intermediate version -- why not...
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|
1304 for key, value in env.items(): |
|
c68a0113b75a
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|
1305 prefix = prefix + '%s=%s\n' % (key, mkarg(value)[1:]) |
| 2048 | 1306 prefix = prefix + 'export %s\n' % key |
| 1307 return os.popen(prefix + cmd, mode) | |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1308 |
|
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|
1309 4.19. Q. What is a class? |
|
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1310 |
|
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|
1311 A. A class is the particular object type that is created by executing |
|
2208
c68a0113b75a
intermediate version -- why not...
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|
1312 a class statement. Class objects are used as templates, to create |
|
c68a0113b75a
intermediate version -- why not...
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|
1313 class instance objects, which embody both the data structure and |
|
c68a0113b75a
intermediate version -- why not...
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|
1314 program routines specific to a datatype. |
|
1903
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|
1315 |
|
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|
1316 4.20. Q. What is a method? |
|
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1317 |
|
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|
1318 A. A method is a function that you normally call as |
|
2208
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|
1319 x.name(arguments...) for some object x. The term is used for methods |
|
1903
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|
1320 of classes and class instances as well as for methods of built-in |
|
2208
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|
1321 objects. (The latter have a completely different implementation and |
|
c68a0113b75a
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|
1322 only share the way their calls look in Python code.) Methods of |
|
c68a0113b75a
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|
1323 classes (and class instances) are defined as functions inside the |
|
c68a0113b75a
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|
1324 class definition. |
|
1903
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1325 |
|
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|
1326 4.21. Q. What is self? |
|
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1327 |
|
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|
1328 A. Self is merely a conventional name for the first argument of a |
|
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|
1329 method -- i.e. a function defined inside a class definition. A method |
|
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|
1330 defined as meth(self, a, b, c) should be called as x.meth(a, b, c) for |
|
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|
1331 some instance x of the class in which the definition occurs; |
|
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|
1332 the called method will think it is called as meth(x, a, b, c). |
|
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1333 |
|
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|
1334 4.22. Q. What is a unbound method? |
|
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1335 |
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|
1336 A. An unbound method is a method defined in a class that is not yet |
|
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|
1337 bound to an instance. You get an unbound method if you ask for a |
|
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|
1338 class attribute that happens to be a function. You get a bound method |
|
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|
1339 if you ask for an instance attribute. A bound method knows which |
| 1942 | 1340 instance it belongs to and calling it supplies the instance automatically; |
|
1903
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|
1341 an unbound method only knows which class it wants for its first |
|
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|
1342 argument (a derived class is also OK). Calling an unbound method |
|
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|
1343 doesn't "magically" derive the first argument from the context -- you |
|
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|
1344 have to provide it explicitly. |
|
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|
1345 |
| 2048 | 1346 4.23. Q. How do I call a method defined in a base class from a derived |
| 1347 class that overrides it? | |
|
1903
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1348 |
|
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|
1349 A. If your class definition starts with "class Derived(Base): ..." |
|
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|
1350 then you can call method meth defined in Base (or one of Base's base |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1351 classes) as Base.meth(self, arguments...). Here, Base.meth is an |
|
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|
1352 unbound method (see previous question). |
|
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|
1353 |
| 2048 | 1354 4.24. Q. How do I call a method from a base class without using the |
| 1355 name of the base class? | |
|
1903
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|
1356 |
|
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|
1357 A. DON'T DO THIS. REALLY. I MEAN IT. It appears that you could call |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1358 self.__class__.__bases__[0].meth(self, arguments...) but this fails when |
| 1942 | 1359 a doubly-derived method is derived from your class: for its instances, |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1360 self.__class__.__bases__[0] is your class, not its base class -- so |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1361 (assuming you are doing this from within Derived.meth) you would start |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1362 a recursive call. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1363 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1364 4.25. Q. How can I organize my code to make it easier to change the base |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1365 class? |
|
e450bd43631a
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|
1366 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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diff
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|
1367 A. You could define an alias for the base class, assign the real base |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
1368 class to it before your class definition, and use the alias throughout |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
1369 your class. Then all you have to change is the value assigned to the |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
1370 alias. Incidentally, this trick is also handy if you want to decide |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1371 dynamically (e.g. depending on availability of resources) which base |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1372 class to use. Example: |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
1373 |
|
4278
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
1374 BaseAlias = <real base class> |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
parents:
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diff
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|
1375 class Derived(BaseAlias): |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
parents:
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diff
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|
1376 def meth(self): |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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diff
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|
1377 BaseAlias.meth(self) |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
1378 ... |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1379 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1380 4.26. Q. How can I find the methods or attributes of an object? |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1381 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1382 A. This depends on the object type. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1383 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1384 For an instance x of a user-defined class, instance attributes are |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1385 found in the dictionary x.__dict__, and methods and attributes defined |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1386 by its class are found in x.__class__.__bases__[i].__dict__ (for i in |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1387 range(len(x.__class__.__bases__))). You'll have to walk the tree of |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1388 base classes to find *all* class methods and attributes. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1389 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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diff
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|
1390 Many, but not all built-in types define a list of their method names |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1391 in x.__methods__, and if they have data attributes, their names may be |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1392 found in x.__members__. However this is only a convention. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1393 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
1394 For more information, read the source of the standard (but |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
1395 undocumented) module newdir. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
1396 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1397 4.27. Q. I can't seem to use os.read() on a pipe created with os.popen(). |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
1398 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1399 A. os.read() is a low-level function which takes a file descriptor (a |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1400 small integer). os.popen() creates a high-level file object -- the |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1401 same type used for sys.std{in,out,err} and returned by the builtin |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
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|
1402 open() function. Thus, to read n bytes from a pipe p created with |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1403 os.popen(), you need to use p.read(n). |
| 1529 | 1404 |
| 1942 | 1405 4.28. Q. How can I create a stand-alone binary from a Python script? |
| 1406 | |
| 1407 The demo script "Demo/scripts/freeze.py" does what you want. (It's | |
| 1408 actually not a demo but a support tool -- there is some extra code in | |
| 1409 the interpreter to accommodate it.) It requires that you have the | |
| 1410 Python build tree handy, complete with all the lib*.a files. | |
| 1411 | |
| 1412 This works by scanning your source recursively for import statements | |
| 1413 (both forms) and looking for the modules on the standard Python path | |
| 1414 as well as in the source directory (for built-in modules). It then | |
| 1415 "compiles" the modules written in Python to C code (array initializers | |
| 1416 that can be turned into code objects using the marshal module) and | |
| 1417 creates a custom-made config file that only contains those built-in | |
| 1418 modules which are actually used in the program. It then compiles the | |
| 1419 generated C code and links it with the rest of the Python interpreter | |
| 1420 to form a self-contained binary which acts exactly like your script. | |
| 1421 | |
|
2716
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1422 Hint: the freeze program only works if your script's filename ends in |
|
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
2661
diff
changeset
|
1423 ".py". |
| 1942 | 1424 |
|
2716
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1425 4.29. Q. What WWW tools are there for Python? |
| 1942 | 1426 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1427 A. See the chapter titled "Internet and WWW" in the Library Reference |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
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|
1428 Manual. There's also a web browser written in Python, called Grail -- |
|
4563
ea458933fc2a
monty -> grail in Grail URL.
Guido van Rossum <guido@python.org>
parents:
4543
diff
changeset
|
1429 see <URL:http://grail.cnri.reston.va.us/grail/>. |
| 1942 | 1430 |
| 1431 Steve Miale <smiale@cs.indiana.edu> has written a modular WWW browser | |
| 1432 called Dancer. An alpha version can be FTP'ed from | |
| 2048 | 1433 <URL:ftp://ftp.cs.indiana.edu/pub/smiale/dancer.tar.gz>. (There are a |
| 1434 few articles about Dancer in the (hyper)mail archive | |
| 1435 <URL:http://www.cwi.nl/~guido/hypermail/python-1994q3/index.html>.) | |
| 1942 | 1436 |
|
2716
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next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1437 4.30. Q. How do I run a subprocess with pipes connected to both input |
|
2208
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1438 and output? |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1439 |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1440 A. This is really a UNIX question. Also, in general, it is unwise to |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1441 do so, because you can easily cause a deadlock where the parent |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1442 process is blocked waiting for output from the child, while the child |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1443 is blocked waiting for input from the child. This can be caused |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1444 because the parent expects the child to output more text than it does, |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1445 or it can be caused by data being stuck in stdio buffers due to lack |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1446 of flushing. The Python parent can of course explicitly flush the data |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1447 it sends to the child before it reads any output, but if the child is |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1448 a naive C program it can easily have been written to never explicitly |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1449 flush its output, even if it is interactive, since flushing is |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1450 normally automatic. |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1451 |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1452 In many cases, all you really need is to run some data through a |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1453 command and get the result back. Unless the data is infinite in size, |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1454 the easiest (and often the most efficient!) way to do this is to write |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1455 it to a temporary file and run the command with that temporary file as |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1456 input. The standard module tempfile exports a function mktemp() which |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1457 generates unique temporary file names. |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1458 |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1459 If after reading all of the above you still want to connect two pipes |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1460 to a subprocess's standard input and output, here's a simple solution, |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1461 due to Jack Jansen: |
|
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
1462 |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
3126
diff
changeset
|
1463 import os |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1464 import sys |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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|
1465 import string |
|
2208
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1466 |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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changeset
|
1467 MAXFD = 100 # Max number of file descriptors in this system |
|
2208
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1468 |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1469 def popen2(cmd): |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
3126
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changeset
|
1470 cmd = string.split(cmd) |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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|
1471 p2cread, p2cwrite = os.pipe() |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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changeset
|
1472 c2pread, c2pwrite = os.pipe() |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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changeset
|
1473 pid = os.fork() |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1474 if pid == 0: |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1475 # Child |
|
0ed5cd8df51f
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Guido van Rossum <guido@python.org>
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changeset
|
1476 os.close(0) |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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|
1477 os.close(1) |
|
3727
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
1478 if os.dup(p2cread) != 0: |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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changeset
|
1479 sys.stderr.write('popen2: bad read dup\n') |
|
3727
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
parents:
3233
diff
changeset
|
1480 if os.dup(c2pwrite) != 1: |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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|
1481 sys.stderr.write('popen2: bad write dup\n') |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1482 for i in range(3, MAXFD): |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1483 try: |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1484 os.close(i) |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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diff
changeset
|
1485 except: |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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diff
changeset
|
1486 pass |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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diff
changeset
|
1487 try: |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1488 os.execv(cmd[0], cmd) |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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|
1489 finally: |
|
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1490 os._exit(1) |
|
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1491 os.close(p2cread) |
|
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1492 tochild = os.fdopen(p2cwrite, 'w') |
|
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|
1493 os.close(c2pwrite) |
|
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1494 fromchild = os.fdopen(c2pread, 'r') |
|
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1495 return fromchild, tochild |
|
2208
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intermediate version -- why not...
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|
1496 |
|
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|
1497 Note that many interactive programs (e.g. vi) don't work well with |
|
c68a0113b75a
intermediate version -- why not...
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|
1498 pipes substituted for standard input and output. You will have to use |
|
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intermediate version -- why not...
Guido van Rossum <guido@python.org>
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|
1499 pseudo ttys ("ptys") instead of pipes. There is some undocumented |
|
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|
1500 code to use these in the library module pty.py -- I'm afraid you're on |
| 2855 | 1501 your own here. |
| 1502 | |
| 1503 A different answer is a Python interface to Don Libes' "expect" | |
| 1504 library. A prerelease of this is available on the Python ftp mirror | |
| 1505 sites in the contrib subdirectory as expy-0.3.tar.gz, e.g. | |
| 1506 <URL:ftp://ftp.python.org/pub/python/contrib/expy-0.3.tar.gz>. | |
|
2208
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|
1507 |
|
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|
1508 4.31. Q. How do I call a function if I have the arguments in a tuple? |
|
2660
4eb6ddb9e961
Some more changes for 1.2
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|
1509 |
|
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|
1510 A. Use the built-in function apply(). For instance, |
|
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|
1511 |
|
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|
1512 func(1, 2, 3) |
|
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|
1513 |
|
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|
1514 is equivalent to |
|
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|
1515 |
|
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|
1516 args = (1, 2, 3) |
|
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|
1517 apply(func, args) |
|
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|
1518 |
|
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|
1519 Note that func(args) is not the same -- it calls func() with exactly |
|
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|
1520 one argument, the tuple args, instead of three arguments, the integers |
|
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|
1521 1, 2 and 3. |
|
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|
1522 |
|
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|
1523 4.32. Q. How do I enable font-lock-mode for Python in Emacs? |
|
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|
1524 |
|
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|
1525 A. Assuming you're already using python-mode and font-lock-mode |
|
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|
1526 separately, all you need to do is put this in your .emacs file: |
|
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|
1527 |
|
3207
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|
1528 (defun my-python-mode-hook () |
|
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|
1529 (setq font-lock-keywords python-font-lock-keywords) |
|
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|
1530 (font-lock-mode 1)) |
|
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|
1531 (add-hook 'python-mode-hook 'my-python-mode-hook) |
|
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|
1532 |
|
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|
1533 4.33. Q. Is there an inverse to the format operator (a la C's scanf())? |
|
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|
1534 |
|
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|
1535 A. Not as such. |
|
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|
1536 |
|
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|
1537 For simple input parsing, the easiest approach is usually to split |
|
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|
1538 the line into whitespace-delimited words using string.split(), and to |
|
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|
1539 convert decimal strings to numeric values using string.atoi(), |
|
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|
1540 string.atol() or string.atof(). (Python's atoi() is 32-bit and its |
|
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|
1541 atol() is arbitrary precision.) If you want to use another delimiter |
|
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|
1542 than whitespace, use string.splitfield() (possibly combining it with |
|
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|
1543 string.strip() which removes surrounding whitespace from a string). |
|
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|
1544 |
|
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|
1545 For more complicated input parsing, regular expressions (see module |
|
19b1195a3af8
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Guido van Rossum <guido@python.org>
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|
1546 regex) are better suited and more powerful than C's scanf(). |
|
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|
1547 |
|
3727
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|
1548 4.34. Q. Can I have Tk events handled while waiting for I/O? |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1549 |
|
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|
1550 A. Yes, and you don't even need threads! But you'll have to |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1551 restructure your I/O code a bit. Tk has the equivalent of Xt's |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1552 XtAddInput() call, which allows you to register a callback function |
|
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Some updates. Still out of date.
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|
1553 which will be called from the Tk mainloop when I/O is possible on a |
|
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Some updates. Still out of date.
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|
1554 file descriptor. Here's what you need: |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1555 |
|
4278
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
1556 from Tkinter import tkinter |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
1557 tkinter.createfilehandler(file, mask, callback) |
|
3727
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|
1558 |
|
a10a0f6014c4
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|
1559 The file may be a Python file or socket object (actually, anything |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1560 with a fileno() method), or an integer file descriptor. The mask is |
|
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Some updates. Still out of date.
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|
1561 one of the constants tkinter.READABLE or tkinter.WRITABLE. The |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1562 callback is called as follows: |
|
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Some updates. Still out of date.
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|
1563 |
|
4278
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Guido van Rossum <guido@python.org>
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|
1564 callback(file, mask) |
|
3727
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|
1565 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1566 You must unregister the callback when you're done, using |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1567 |
|
4278
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Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
1568 tkinter.deletefilehandler(file) |
|
3727
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Some updates. Still out of date.
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|
1569 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1570 Note: since you don't know *how many bytes* are available for reading, |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1571 you can't use the Python file object's read or readline methods, since |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1572 these will insist on reading a predefined number of bytes. For |
|
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Some updates. Still out of date.
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|
1573 sockets, the recv() or recvfrom() methods will work fine; for other |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1574 files, use os.read(file.fileno(), maxbytecount). |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1575 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1576 4.35. Q. How do I write a function with output parameters (call by reference)? |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1577 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1578 A. [Mark Lutz] The thing to remember is that arguments are passed by |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1579 assignment in Python. Since assignment just creates references to |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1580 objects, there's no alias between an argument name in the caller and |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1581 callee, and so no call-by-reference per se. But you can simulate it |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1582 in a number of ways: |
|
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Some updates. Still out of date.
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|
1583 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1584 1) By using global variables; but you probably shouldn't :-) |
|
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Some updates. Still out of date.
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|
1585 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1586 2) By passing a mutable (changeable in-place) object: |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1587 |
|
a10a0f6014c4
Some updates. Still out of date.
Guido van Rossum <guido@python.org>
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|
1588 def func1(a): |
|
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|
1589 a[0] = 'new-value' # 'a' references a mutable list |
|
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Some updates. Still out of date.
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|
1590 a[1] = a[1] + 1 # changes a shared object |
|
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Some updates. Still out of date.
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|
1591 |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1592 args = ['old-value', 99] |
|
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|
1593 func1(args) |
|
a10a0f6014c4
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|
1594 print args[0], args[1] # output: new-value 100 |
|
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Some updates. Still out of date.
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|
1595 |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1596 3) By return a tuple, holding the final values of arguments: |
|
a10a0f6014c4
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|
1597 |
|
a10a0f6014c4
Some updates. Still out of date.
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|
1598 def func2(a, b): |
|
a10a0f6014c4
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|
1599 a = 'new-value' # a and b are local names |
|
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|
1600 b = b + 1 # assigned to new objects |
|
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|
1601 return a, b # return new values |
|
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|
1602 |
|
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|
1603 x, y = 'old-value', 99 |
|
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|
1604 x, y = func2(x, y) |
|
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|
1605 print x, y # output: new-value 100 |
|
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|
1606 |
|
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|
1607 4) And other ideas that fall-out from Python's object model. For |
|
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|
1608 instance, it might be clearer to pass in a mutable dictionary: |
|
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Some updates. Still out of date.
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|
1609 |
|
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Some updates. Still out of date.
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|
1610 def func3(args): |
|
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Some updates. Still out of date.
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|
1611 args['a'] = 'new-value' # args is a mutable dictionary |
|
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Some updates. Still out of date.
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|
1612 args['b'] = args['b'] + 1 # change it in-place |
|
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Some updates. Still out of date.
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|
1613 |
|
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Some updates. Still out of date.
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|
1614 args = {'a':' old-value', 'b': 99} |
|
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Some updates. Still out of date.
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|
1615 func3(args) |
|
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|
1616 print args['a'], args['b'] |
|
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|
1617 |
|
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|
1618 5) Or bundle-up values in a class instance: |
|
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|
1619 |
|
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|
1620 class callByRef: |
|
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|
1621 def __init__(self, **args): |
|
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|
1622 for (key, value) in args.items(): |
|
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|
1623 setattr(self, key, value) |
|
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|
1624 |
|
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|
1625 def func4(args): |
|
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|
1626 args.a = 'new-value' # args is a mutable callByRef |
|
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Some updates. Still out of date.
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|
1627 args.b = args.b + 1 # change object in-place |
|
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|
1628 |
|
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Some updates. Still out of date.
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|
1629 args = callByRef(a='old-value', b=99) |
|
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Some updates. Still out of date.
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|
1630 func4(args) |
|
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|
1631 print args.a, args.b |
|
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|
1632 |
|
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|
1633 But there's probably no good reason to get this complicated :-). |
|
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Some updates. Still out of date.
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|
1634 |
|
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|
1635 [Python' author favors solution 3 in most cases.] |
|
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|
1636 |
|
3865
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Added two new questions; about globals/locals and about recursive imports.
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|
1637 4.36. Q. Please explain the rules for local and global variables in Python. |
|
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Added two new questions; about globals/locals and about recursive imports.
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|
1638 |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1639 A. [Ken Manheimer] In Python, procedure variables are implicitly |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1640 global, unless they assigned anywhere within the block. In that case |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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parents:
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changeset
|
1641 they are implicitly local, and you need to explicitly declare them as |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1642 'global'. |
|
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Added two new questions; about globals/locals and about recursive imports.
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|
1643 |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
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changeset
|
1644 Though a bit surprising at first, a moments consideration explains |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
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|
1645 this. On one hand, requirement of 'global' for assigned vars provides |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
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|
1646 a bar against unintended side-effects. On the other hand, if global |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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|
1647 were required for all global references, you'd be using global all the |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1648 time. Eg, you'd have to declare as global every reference to a |
|
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Added two new questions; about globals/locals and about recursive imports.
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parents:
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changeset
|
1649 builtin function, or to a component of an imported module. This |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1650 clutter would defeat the usefulness of the 'global' declaration for |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
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changeset
|
1651 identifying side-effects. |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1652 |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1653 4.37. Q. How can I have modules that mutually import each other? |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
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|
1654 |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1655 A. Jim Roskind recommends the following order in each module: |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1656 |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
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|
1657 First: all exports (like globals, functions, and classes that don't |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
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|
1658 need imported bases classes). |
|
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Added two new questions; about globals/locals and about recursive imports.
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|
1659 |
|
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Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
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|
1660 Then: all import statements. |
|
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Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
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|
1661 |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1662 Finally: all active code (including globals that are initialized from |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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|
1663 imported values). |
|
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Added two new questions; about globals/locals and about recursive imports.
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|
1664 |
|
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Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1665 Python's author doesn't like this approach much because the imports |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1666 appear in a strange place, but has to admit that it works. His |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1667 recommended strategy is to avoid all uses of "from <module> import *" |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1668 (so everything from an imported module is referenced as |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1669 <module>.<name>) and to place all code inside functions. |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1670 Initializations of global variables and class variables should use |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1671 constants or built-in functions only. |
|
4591035228a7
Added two new questions; about globals/locals and about recursive imports.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1672 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1673 4.38. Q. How do I copy an object in Python? |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1674 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1675 A. There is no generic copying operation built into Python, however |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1676 most object types have some way to create a clone. Here's how for the |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1677 most common objects: |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1678 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1679 - For immutable objects (numbers, strings, tuples), cloning is |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1680 unnecessary since their value can't change. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1681 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1682 - For lists (and generally for mutable sequence types), a clone is |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1683 created by the expression l[:]. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1684 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1685 - For dictionaries, the following function returns a clone: |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1686 |
|
4278
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
parents:
4250
diff
changeset
|
1687 def dictclone(o): |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
parents:
4250
diff
changeset
|
1688 n = {} |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
parents:
4250
diff
changeset
|
1689 for k in o.keys(): n[k] = o[k] |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1690 return n |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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changeset
|
1691 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
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changeset
|
1692 - Finally, for generic objects, the "copy" module defines two |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1693 functions for copying objects. copy.copy(x) returns a copy as shown |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1694 by the above rules. copy.deepcopy(x) also copies the elements of |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1695 composite objects. See the section on this module in the Library |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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changeset
|
1696 Reference Manual. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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diff
changeset
|
1697 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
4221
diff
changeset
|
1698 4.39. Q. How to implement persistent objects in Python? (Persistent == |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1699 automatically saved to and restored from disk.) |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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changeset
|
1700 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1701 A. The library module "pickle" now solves this in a very general way |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1702 (though you still can't store things like open files, sockests or |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
1703 windows), and the library module "shelve" uses pickle and (g)dbm to |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
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parents:
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diff
changeset
|
1704 create presistent mappings containing arbitrary Python objects. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
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diff
changeset
|
1705 |
|
4438
e88b3215e94a
Added question about error from misuse of mangled names.
Guido van Rossum <guido@python.org>
parents:
4408
diff
changeset
|
1706 4.40. Q. I try to use __spam and I get an error about _SomeClassName__spam. |
|
e88b3215e94a
Added question about error from misuse of mangled names.
Guido van Rossum <guido@python.org>
parents:
4408
diff
changeset
|
1707 |
|
e88b3215e94a
Added question about error from misuse of mangled names.
Guido van Rossum <guido@python.org>
parents:
4408
diff
changeset
|
1708 A. Variables with double leading underscore are "mangled" to provide a |
|
e88b3215e94a
Added question about error from misuse of mangled names.
Guido van Rossum <guido@python.org>
parents:
4408
diff
changeset
|
1709 simple but effective way to define class private variables. See the |
|
e88b3215e94a
Added question about error from misuse of mangled names.
Guido van Rossum <guido@python.org>
parents:
4408
diff
changeset
|
1710 chapter "New in Release 1.4" in the Python Tutorial. |
|
e88b3215e94a
Added question about error from misuse of mangled names.
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4408
diff
changeset
|
1711 |
|
4543
e52054440efc
Added os.remove()/unlink(), rmdir(), rename(), and [f]truncate().
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4542
diff
changeset
|
1712 4.41. Q. How do I delete a file? And other file questions. |
|
e52054440efc
Added os.remove()/unlink(), rmdir(), rename(), and [f]truncate().
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diff
changeset
|
1713 |
|
e52054440efc
Added os.remove()/unlink(), rmdir(), rename(), and [f]truncate().
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diff
changeset
|
1714 A. Use os.remove(filename) or os.unlink(filename); for documentation, |
|
e52054440efc
Added os.remove()/unlink(), rmdir(), rename(), and [f]truncate().
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diff
changeset
|
1715 see the posix section of the library manual. They are the same, |
|
e52054440efc
Added os.remove()/unlink(), rmdir(), rename(), and [f]truncate().
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diff
changeset
|
1716 unlink() is simply the Unix name for this function. In earlier |
|
e52054440efc
Added os.remove()/unlink(), rmdir(), rename(), and [f]truncate().
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diff
changeset
|
1717 versions of Python, only os.unlink() was available. |
|
e52054440efc
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1718 |
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|
1719 To remove a directory, use os.rmdir(); use os.mkdir() to create one. |
|
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|
1720 |
|
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|
1721 To rename a file, use os.rename(). |
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|
1722 |
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|
1723 To truncate a file, open it using f = open(filename, "w+"), and use |
|
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|
1724 f.truncate(offset); offset defaults to the current seek position. |
|
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|
1725 There's also os.ftruncate(fd, offset) for files opened with os.open() |
|
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|
1726 -- for advanced Unix hacks only. |
|
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|
1727 |
| 1942 | 1728 |
| 1529 | 1729 5. Extending Python |
| 1730 =================== | |
| 1731 | |
| 1732 5.1. Q. Can I create my own functions in C? | |
| 1733 | |
| 1734 A. Yes, you can create built-in modules containing functions, | |
|
1541
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
1735 variables, exceptions and even new types in C. This is explained in |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
1736 the document "Extending and Embedding the Python Interpreter" (the |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
1737 LaTeX file Doc/ext.tex). Also read the chapter on dynamic loading. |
| 1529 | 1738 |
| 1739 5.2. Q. Can I create my own functions in C++? | |
| 1740 | |
| 1741 A. Yes, using the C-compatibility features found in C++. Basically | |
| 1742 you place extern "C" { ... } around the Python include files and put | |
| 1743 extern "C" before each function that is going to be called by the | |
| 1744 Python interpreter. Global or static C++ objects with constructors | |
| 1745 are probably not a good idea. | |
| 1746 | |
| 1663 | 1747 5.3. Q. How can I execute arbitrary Python statements from C? |
| 1748 | |
| 1749 A. The highest-level function to do this is run_command() which takes | |
| 1750 a single string argument which is executed in the context of module | |
| 1751 __main__ and returns 0 for success and -1 when an exception occurred | |
| 1752 (including SyntaxError). If you want more control, use run_string(); | |
| 1753 see the source for run_command() in Python/pythonrun.c. | |
| 1754 | |
| 1755 5.4. Q. How can I evaluate an arbitrary Python expression from C? | |
| 1756 | |
| 1757 A. Call the function run_string() from the previous question with the | |
| 1758 start symbol eval_input; it then parses an expression, evaluates it | |
| 1759 and returns its value. See exec_eval() in Python/bltinmodule.c. | |
| 1760 | |
| 1761 5.5. Q. How do I extract C values from a Python object? | |
| 1762 | |
| 1763 A. That depends on the object's type. If it's a tuple, | |
| 1764 gettuplesize(o) returns its length and gettupleitem(o, i) returns its | |
| 1765 i'th item; similar for lists with getlistsize(o) and getlistitem(o, | |
| 1766 i). For strings, getstringsize(o) returns its length and | |
| 1767 getstringvalue(o) a pointer to its value (note that Python strings may | |
| 1768 contain null bytes so strlen() is not safe). To test which type an | |
| 1769 object is, first make sure it isn't NULL, and then use | |
| 1770 is_stringobject(o), is_tupleobject(o), is_listobject(o) etc. | |
| 1771 | |
| 1772 5.6. Q. How do I use mkvalue() to create a tuple of arbitrary length? | |
| 1773 | |
| 1774 A. You can't. Use t = newtupleobject(n) instead, and fill it with | |
| 1775 objects using settupleitem(t, i, o) -- note that this "eats" a | |
| 1776 reference count of o. Similar for lists with newlistobject(n) and | |
|
1903
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|
1777 setlistitem(l, i, o). Note that you *must* set all the tuple items to |
|
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|
1778 some value before you pass the tuple to Python code -- |
|
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|
1779 newtupleobject(n) initializes them to NULL, which isn't a valid Python |
|
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|
1780 value. |
|
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|
1781 |
|
4250
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|
1782 5.7. Q. How do I call an object's method from C? |
|
1903
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1783 |
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|
1784 A. Here's a function (untested) that might become part of the next |
|
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|
1785 release in some form. It uses <stdarg.h> to allow passing the |
|
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|
1786 argument list on to vmkvalue(): |
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|
1787 |
| 2048 | 1788 object *call_method(object *inst, char *methodname, char *format, ...) |
| 1789 { | |
| 1790 object *method; | |
| 1791 object *args; | |
| 1792 object *result; | |
| 1793 va_list va; | |
| 1794 method = getattr(inst, methodname); | |
| 1795 if (method == NULL) return NULL; | |
| 1796 va_start(va, format); | |
| 1797 args = vmkvalue(format, va); | |
| 1798 va_end(va); | |
| 1799 if (args == NULL) { | |
| 1800 DECREF(method); | |
| 1801 return NULL; | |
| 1802 } | |
| 1803 result = call_object(method, args); | |
| 1804 DECREF(method); | |
| 1805 DECREF(args); | |
| 1806 return result; | |
| 1807 } | |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1808 |
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|
1809 This works for any instance that has methods -- whether built-in or |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1810 user-defined. You are responsible for eventually DECREF'ing the |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1811 return value. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1812 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1813 To call, e.g., a file object's "seek" method with arguments 10, 0 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1814 (assuming the file object pointer is "f"): |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1815 |
| 2048 | 1816 res = call_method(f, "seek", "(OO)", 10, 0); |
| 1817 if (res == NULL) { | |
| 1818 ... an exception occurred ... | |
| 1819 } | |
| 1820 else { | |
| 1821 DECREF(res); | |
| 1822 } | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1823 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1824 Note that since call_object() *always* wants a tuple for the argument |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1825 list, to call a function without arguments, pass "()" for the format, |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1826 and to call a function with one argument, surround the argument in |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1827 parentheses, e.g. "(i)". |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1828 |
|
4250
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Removed some obsolete questions and references to version 1.2.
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|
1829 5.8. Q. How do I catch the output from print_error()? |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1830 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1831 A. (Due to Mark Hammond): |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1832 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1833 * in Python code, define an object that supports the "write()" method. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1834 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1835 * redirect sys.stdout and sys.stderr to this object. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1836 |
| 1942 | 1837 * call print_error, or just allow the standard traceback mechanism to |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1838 work. |
|
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|
1839 |
| 1942 | 1840 Then, the output will go wherever your write() method sends it. |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1841 |
|
4250
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Removed some obsolete questions and references to version 1.2.
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|
1842 5.9. Q. How do I access a module written in Python from C? |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1843 |
|
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|
1844 A. You can get a pointer to the module object as follows: |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1845 |
| 2048 | 1846 module = import_module("<modulename>"); |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1847 |
|
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|
1848 If the module hasn't been imported yet (i.e. it is not yet present in |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1849 sys.modules), this initializes the module; otherwise it simply returns |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1850 the value of sys.modules["<modulename>"]. Note that it doesn't enter |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1851 the module into any namespace -- it only ensures it has been |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1852 initialized and is stored in sys.modules. |
|
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|
1853 |
|
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|
1854 You can then access the module's attributes (i.e. any name defined in |
|
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|
1855 the module) as follows: |
|
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|
1856 |
| 2048 | 1857 attr = getattr(module, "<attrname>"); |
|
1903
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|
1858 |
|
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|
1859 Calling setattr(), to assign to variables in the module, also works. |
| 1663 | 1860 |
|
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|
1861 5.10. Q. How do I interface to C++ objects from Python? |
|
3023
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|
1862 |
|
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|
1863 A. Depending on your requirements, there are many approaches. Begin |
|
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|
1864 by reading the "Extending and Embedding" document (Doc/ext.tex, see |
|
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|
1865 also <URL:http://www.python.org/doc/>). Realize that for the Python |
|
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|
1866 run-time system, there isn't a whole lot of difference between C and |
|
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|
1867 C++ -- so the strategy to build a new Python type around a C structure |
|
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|
1868 (pointer) type will also work for C++ objects. |
|
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|
1869 |
|
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|
1870 Automatic generation of interfaces between Python and C++ is still at |
|
87847228b158
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|
1871 the horizon -- parsing C++ header files requires an almost complete |
|
87847228b158
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|
1872 C++ parser, and many features aren't easily translated from C++ to |
|
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|
1873 Python: certain forms of operator oveloading, function overloading |
|
87847228b158
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|
1874 (best approached by a varargs function which explicitly type-checks |
|
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|
1875 its arguments), and reference arguments are just a number of features |
|
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|
1876 that are hard to translate correctly if at all. |
|
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|
1877 |
|
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|
1878 The hardest problem is to transparently translate the C++ class |
|
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|
1879 hierarchy to Python, so that Python programs derive classes from C++ |
|
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|
1880 classes. Given suitable constraints, this may be possible, but it |
|
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|
1881 would require more space than I have in this FAQ to explain how. |
|
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|
1882 In any case, you can get quite a bit done without this, using just the |
|
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|
1883 existing classes from Python. |
|
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|
1884 |
|
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|
1885 If this all seems rather daunting, that may be because it is -- C++ |
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1886 isn't exactly a baby to handle without gloves! However, people have |
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1887 accomplished amazing feats of interfacing between Python and C++, and |
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1888 a detailed question posted to the Python list is likely to elicit some |
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1889 interesting and useful responses. |
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1890 |
| 1529 | 1891 |
| 1892 6. Python's design | |
| 1893 ================== | |
| 1894 | |
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1895 6.1. Q. Why isn't there a switch or case statement in Python? |
| 1529 | 1896 |
| 1897 A. You can do this easily enough with a sequence of | |
| 1898 if... elif... elif... else. There have been some proposals for switch | |
| 1942 | 1899 statement syntax, but there is no consensus (yet) on whether and how |
| 1529 | 1900 to do range tests. |
| 1901 | |
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1902 6.2. Q. Why does Python use indentation for grouping of statements? |
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1903 |
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1904 A. Basically I believe that using indentation for grouping is |
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1905 extremely elegant and contributes a lot to the clarity of the average |
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1906 Python program. Most people learn to love this feature after a while. |
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1907 Some arguments for it: |
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1908 |
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1909 - Since there are no begin/end brackets there cannot be a disagreement |
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1910 between grouping perceived by the parser and the human reader. I |
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1911 remember long ago seeing a C fragment like this: |
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1912 |
| 2048 | 1913 if (x <= y) |
| 1914 x++; | |
| 1915 y--; | |
| 1916 z++; | |
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1917 |
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1918 and staring a long time at it wondering why y was being decremented |
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1919 even for x > y... (And I wasn't a C newbie then either.) |
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1920 |
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1921 - Since there are no begin/end brackets, Python is much less prone to |
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1922 coding-style conflicts. In C there are loads of different ways to |
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1923 place the braces (including the choice whether to place braces around |
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1924 single statements in certain cases, for consistency). If you're used |
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1925 to reading (and writing) code that uses one style, you will feel at |
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1926 least slightly uneasy when reading (or being required to write) |
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1927 another style. |
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1928 |
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1929 - Many coding styles place begin/end brackets on a line by themself. |
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1930 This makes programs considerably longer and wastes valuable screen |
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1931 space, making it harder to get a good overview over a program. |
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1932 Ideally, a function should fit on one basic tty screen (say, 20 |
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1933 lines). 20 lines of Python are worth a LOT more than 20 lines of C. |
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1934 This is not solely due to the lack of begin/end brackets (the lack of |
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1935 declarations also helps, and the powerful operations of course), but |
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1936 it certainly helps! |
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1937 |
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1938 6.3. Q. Why are Python strings immutable? |
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1939 |
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1940 A. There are two advantages. One is performance: knowing that a |
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1941 string is immutable makes it easy to lay it out at construction time |
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1942 -- fixed and unchanging storage requirements. (This is also one of |
| 1942 | 1943 the reasons for the distinction between tuples and lists.) The |
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1944 other is that strings in Python are considered as "elemental" as |
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1945 numbers. No amount of activity will change the value 8 to anything |
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1946 else, and in Python, no amount of activity will change the string |
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1947 "eight" to anything else. (Adapted from Jim Roskind) |
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1948 |
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1949 6.4. Q. Why don't strings have methods like index() or sort(), like |
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1950 lists? |
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1951 |
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1952 A. Good question. Strings currently don't have methods at all |
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1953 (likewise tuples and numbers). Long ago, it seemed unnecessary to |
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1954 implement any of these functions in C, so a standard library module |
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1955 "string" written in Python was created that performs string related |
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1956 operations. Since then, the cry for performance has moved most of |
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1957 them into the built-in module strop (this is imported by module |
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1958 string, which is still the preferred interface, without loss of |
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1959 performance except during initialization). Some of these functions |
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1960 (e.g. index()) could easily be implemented as string methods instead, |
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1961 but others (e.g. sort()) can't, since their interface prescribes that |
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1962 they modify the object, while strings are immutable (see the previous |
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1963 question). |
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1964 |
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1965 6.5. Q. Why does Python use methods for some functionality |
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1966 (e.g. list.index()) but functions for other (e.g. len(list))? |
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1967 |
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1968 A. Functions are used for those operations that are generic for a |
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1969 group of types and which should work even for objects that don't have |
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1970 methods at all (e.g. numbers, strings, tuples). Also, implementing |
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1971 len(), max(), min() as a built-in function is actually less code than |
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1972 implementing them as methods for each type. One can quibble about |
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1973 individual cases but it's really too late to change such things |
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1974 fundamentally now. |
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1975 |
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1976 6.6. Q. Why can't I derive a class from built-in types (e.g. lists or |
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1977 files)? |
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1978 |
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1979 A. This is caused by the relatively late addition of (user-defined) |
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1980 classes to the language -- the implementation framework doesn't easily |
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1981 allow it. See the answer to question 4.2 for a work-around. This |
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1982 *may* be fixed in the (distant) future. |
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1983 |
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1984 6.7. Q. Why must 'self' be declared and used explicitly in method |
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1985 definitions and calls? |
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1986 |
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1987 A. By asking this question you reveal your C++ background. :-) |
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1988 When I added classes, this was (again) the simplest way of |
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1989 implementing methods without too many changes to the interpreter. I |
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1990 borrowed the idea from Modula-3. It turns out to be very useful, for |
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1991 a variety of reasons. |
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1992 |
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1993 First, it makes it more obvious that you are using a method or |
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1994 instance attribute instead of a local variable. Reading "self.x" or |
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1995 "self.meth()" makes it absolutely clear that an instance variable or |
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1996 method is used even if you don't know the class definition by heart. |
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1997 In C++, you can sort of tell by the lack of a local variable |
| 1942 | 1998 declaration (assuming globals are rare or easily recognizable) -- but |
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1999 in Python, there are no local variable declarations, so you'd have to |
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2000 look up the class definition to be sure. |
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2001 |
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2002 Second, it means that no special syntax is necessary if you want to |
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2003 explicitly reference or call the method from a particular class. In |
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2004 C++, if you want to use a method from base class that is overridden in |
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2005 a derived class, you have to use the :: operator -- in Python you can |
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2006 write baseclass.methodname(self, <argument list>). This is |
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2007 particularly useful for __init__() methods, and in general in cases |
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2008 where a derived class method wants to extend the base class method of |
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|
2009 the same name and thus has to call the base class method somehow. |
|
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Version 1.11 -- added several new answers on design questions
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|
2010 |
|
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Version 1.11 -- added several new answers on design questions
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|
2011 Lastly, for instance variables, it solves a syntactic problem with |
|
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Version 1.11 -- added several new answers on design questions
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|
2012 assignment: since local variables in Python are (by definition!) those |
|
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
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|
2013 variables to which a value assigned in a function body (and that |
|
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Version 1.11 -- added several new answers on design questions
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|
2014 aren't explicitly declared global), there has to be some way to tell |
|
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Version 1.11 -- added several new answers on design questions
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|
2015 the interpreter that an assignment was meant to assign to an instance |
|
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Version 1.11 -- added several new answers on design questions
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|
2016 variable instead of to a local variable, and it should preferably be |
|
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
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|
2017 syntactic (for efficiency reasons). C++ does this through |
|
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Version 1.11 -- added several new answers on design questions
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|
2018 declarations, but Python doesn't have declarations and it would be a |
|
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Version 1.11 -- added several new answers on design questions
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|
2019 pity having to introduce them just for this purpose. Using the |
|
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Version 1.11 -- added several new answers on design questions
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2020 explicit "self.var" solves this nicely. Similarly, for using instance |
|
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
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|
2021 variables, having to write "self.var" means that references to |
|
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
Guido van Rossum <guido@python.org>
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|
2022 unqualified names inside a method don't have to search the instance's |
|
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
Guido van Rossum <guido@python.org>
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|
2023 directories. |
|
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
Guido van Rossum <guido@python.org>
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|
2024 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
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|
2025 6.8. Q. Can't you emulate threads in the interpreter instead of |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2026 relying on an OS-specific thread implementation? |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2027 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2028 A. Unfortunately, the interpreter pushes at least one C stack frame |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2029 for each Python stack frame. Also, extensions can call back into |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
1902
diff
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|
2030 Python at almost random moments. Therefore a complete threads |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2031 implementation requires thread support for C. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2032 |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
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|
2033 6.9. Q. Why can't lambda forms contain statements? |
| 1942 | 2034 |
| 2035 A. Python lambda forms cannot contain statements because Python's | |
|
2208
c68a0113b75a
intermediate version -- why not...
Guido van Rossum <guido@python.org>
parents:
2048
diff
changeset
|
2036 syntactic framework can't handle statements nested inside expressions. |
| 1942 | 2037 |
| 2038 However, in Python, this is not a serious problem. Unlike lambda | |
| 2039 forms in other languages, where they add functionality, Python lambdas | |
| 2040 are only a shorthand notation if you're too lazy to define a function. | |
| 2041 | |
| 2042 Functions are already first class objects in Python, and can be | |
| 2043 declared in a local scope. Therefore the only advantage of using a | |
| 2044 lambda form instead of a locally-defined function is that you'll have | |
| 2045 to invent a name for the function -- but that's just a local variable | |
| 2046 to which the function object (which is exactly the same type of object | |
| 2047 that a lambda form yields) is assigned! | |
| 2048 | |
|
4250
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Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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|
2049 6.10. Q. Why don't lambdas have access to variables defined in the |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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|
2050 containing scope? |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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|
2051 |
|
4278
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
2052 A. Because they are implemented as ordinary functions. |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
Guido van Rossum <guido@python.org>
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|
2053 See question 4.5 above. |
|
4250
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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2054 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
parents:
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|
2055 6.11. Q. Why can't recursive functions be defined inside other functions? |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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|
2056 |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
Guido van Rossum <guido@python.org>
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|
2057 A. See question 4.5 above. |
|
4470f7ff0c23
Removed some obsolete questions and references to version 1.2.
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|
2058 |
| 1942 | 2059 6.12. Q. Why is there no more efficient way of iterating over a dictionary |
| 2060 than first constructing the list of keys()? | |
| 2061 | |
| 2062 A. Have you tried it? I bet it's fast enough for your purposes! In | |
| 2063 most cases such a list takes only a few percent of the space occupied | |
| 2064 by the dictionary -- it needs only 4 bytes (the size of a pointer) per | |
| 2065 key -- a dictionary costs 8 bytes per key plus between 30 and 70 | |
| 2066 percent hash table overhead, plus the space for the keys and values -- | |
| 2067 by necessity all keys are unique objects and a string object (the most | |
| 2068 common key type) costs at least 18 bytes plus the length of the | |
| 2069 string. Add to that the values contained in the dictionary, and you | |
| 2070 see that 4 bytes more per item really isn't that much more memory... | |
| 2071 | |
| 2072 A call to dict.keys() makes one fast scan over the dictionary | |
| 2073 (internally, the iteration function does exist) copying the pointers | |
| 2074 to the key objects into a pre-allocated list object of the right size. | |
| 2075 The iteration time isn't lost (since you'll have to iterate anyway -- | |
| 2076 unless in the majority of cases your loop terminates very prematurely | |
| 2077 (which I doubt since you're getting the keys in random order). | |
| 2078 | |
| 2079 I don't expose the dictionary iteration operation to Python | |
| 2080 programmers because the dictionary shouldn't be modified during the | |
| 2081 entire iteration -- if it is, there's a very small chance that the | |
| 2082 dictionary is reorganized because the hash table becomes too full, and | |
| 2083 then the iteration may miss some items and see others twice. Exactly | |
| 2084 because this only occurs rarely, it would lead to hidden bugs in | |
| 2085 programs: it's easy never to have it happen during test runs if you | |
| 2086 only insert or delete a few items per iteration -- but your users will | |
| 2087 surely hit upon it sooner or later. | |
| 2088 | |
|
3023
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several new questions, 1.3 beta mentioned
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|
2089 6.13. Q. Can Python be compiled to machine code, C or some other language? |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
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|
2090 |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
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|
2091 A. Not easily. Python's high level data types, dynamic typing of |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
3018
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|
2092 objects and run-time invocation of the interpreter (using eval() or |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
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|
2093 exec) together mean that a "compiled" Python program would probably |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2094 consist mostly of calls into the Python run-time system, even for |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2095 seemingly simple operations like "x+1". Thus, the performance gain |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2096 would probably be minimal. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2097 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2098 Internally, Python source code is always translated into a "virtual |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
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|
2099 machine code" or "byte code" representation before it is interpreted |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
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|
2100 (by the "Python virtual machine" or "bytecode interpreter"). In order |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2101 to avoid the overhead of parsing and translating modules that rarely |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2102 change over and over again, this byte code is written on a file whose |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
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|
2103 name ends in ".pyc" whenever a module is parsed (from a file whose |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
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|
2104 name ends in ".py"). When the corresponding .py file is changed, it |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2105 is parsed and translated again and the .pyc file is rewritten. There |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2106 is no performance difference once the .pyc file has been loaded (the |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2107 bytecode read from the .pyc file is exactly the same as the bytecode |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2108 created by direct translation). The only difference is that loading |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2109 code from a .pyc file is faster than parsing and translating a .py |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2110 file, so the presence of precompiled .pyc files will generally improve |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2111 start-up time of Python scripts. If desired, the Lib/compileall.py |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2112 module/script can be used to force creation of valid .pyc files for a |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2113 given set of modules. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2114 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2115 If you are looking for a way to translate Python programs in order to |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2116 distribute them in binary form, without the need to distribute the |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2117 interpreter and library as well, have a look at the freeze.py script |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2118 in the Tools/freeze directory. This creates a single binary file |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2119 incorporating your program, the Python interpreter, and those parts of |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2120 the Python library that are needed by your program. Of course, the |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2121 resulting binary will only run on the same type of platform as that |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2122 used to create it. |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2123 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2124 Hints for proper usage of freeze.py: |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2125 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2126 - the script must be in a file whose name ends in .py |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2127 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
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|
2128 - you must have installed Python fully: |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2129 |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
3126
diff
changeset
|
2130 make install |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
3126
diff
changeset
|
2131 make libinstall |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
3126
diff
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|
2132 make inclinstall |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
parents:
3126
diff
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|
2133 make libainstall |
|
3023
87847228b158
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|
2134 |
|
3126
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2135 6.14. Q. Why doesn't Python use proper garbage collection? |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2136 |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2137 A. It's looking less and less likely that Python will ever get |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2138 "automatic" garbage collection (GC). For one thing, unless this were |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2139 added to C as a standard feature, it's a portability pain in the ass. |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2140 And yes, I know about the Xerox library. It has bits of assembler |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2141 code for *most* *common* platforms. Not for all. And although it is |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2142 mostly transparent, it isn't completely transparent (when I once |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2143 linked Python with it, it dumped core). |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2144 |
|
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+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2145 "Proper" GC also becomes a problem when Python gets embedded into |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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|
2146 other applications. While in a stand-alone Python it may be fine to |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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|
2147 replace the standard malloc() and free() with versions provided by the |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2148 GC library, an application embedding Python may want to have its *own* |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2149 substitute for malloc() and free(), and may not want Python's. Right |
|
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Guido van Rossum <guido@python.org>
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2150 now, Python works with anything that implements malloc() and free() |
|
e90643f33c64
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Guido van Rossum <guido@python.org>
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2151 properly. |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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|
2152 |
|
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|
2153 Besides, the predictability of destructor calls in Python is kind of |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2154 attractive. With GC, the following code (which is fine in current |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2155 Python) will run out of file descriptors long before it runs out of |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2156 memory: |
|
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+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2157 |
|
3207
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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|
2158 for file in <very long list of files>: |
|
0ed5cd8df51f
all sorts of minor nits
Guido van Rossum <guido@python.org>
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|
2159 f = open(file) |
|
0ed5cd8df51f
all sorts of minor nits
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|
2160 c = file.read(1) |
|
3126
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+aaron watters, +PSA, +GC, -lance, -beta
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|
2161 |
|
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+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2162 Using the current reference counting and destructor scheme, each new |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2163 assignment to f closes the previous file. Using GC, this is not |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2164 guaranteed. Sure, you can think of ways to fix this. But it's not |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2165 off-the-shelf technology. |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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|
2166 |
| 1529 | 2167 |
| 2168 7. Using Python on non-UNIX platforms | |
| 2169 ===================================== | |
| 2170 | |
|
1547
0efa240b1dbc
At the release of 1.0.1
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|
2171 7.1. Q. Is there a Mac version of Python? |
| 1529 | 2172 |
|
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|
2173 A. Yes, see the "mac" subdirectory of the distribution sites, |
|
2716
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next version; python.org changes
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|
2174 e.g. <URL:ftp://ftp.python.org/pub/python/mac/>. |
|
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At the release of 1.0.1
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2175 |
|
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2176 7.2. Q. Are there DOS and Windows versions of Python? |
|
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2177 |
|
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|
2178 A. Yes. There is a plethora of not-always-compatible versions. See |
|
f6e824b27032
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|
2179 the "pythonwin", "wpy", "nt" and "pc" subdirectories of the |
|
f6e824b27032
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|
2180 distribution sites. A quick comparison: |
|
f6e824b27032
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2181 |
|
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|
2182 PythonWin: Extensive support for the 32-bit native Windows API and GUI |
|
f6e824b27032
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|
2183 building using MFC. Windows NT and Windows 95 only (and Windows |
|
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|
2184 3.1(1) using win32s, until Microsoft stops supporting it :-( ). |
|
f6e824b27032
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2185 <URL:ftp://ftp.python.org/pub/python/pythonwin/>. |
|
f6e824b27032
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|
2186 |
|
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|
2187 WPY: Ports to DOS, Windows 3.1(1), Windows 95, Windows NT and OS/2. |
|
f6e824b27032
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2188 Also contains a GUI package that offers portability between Windows |
|
f6e824b27032
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|
2189 (not DOS) and Unix, and native look and feel on both. |
|
f6e824b27032
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|
2190 <URL:ftp://ftp.python.org/pub/python/wpy/>. |
|
f6e824b27032
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|
2191 |
|
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|
2192 NT: Basic ports built straight from the 1.4 distribution for Windows |
|
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|
2193 95 and Windows NT. This will eventually provide core support for |
|
f6e824b27032
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|
2194 both PythonWin and WPY on all 32-bit Microsoft platforms. |
| 2855 | 2195 <URL:ftp://ftp.python.org/pub/python/nt/>. |
| 2196 | |
|
4278
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|
2197 PC: Old, unsupported ports to DOS, Windows 3.1(1) and OS/2. |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
2198 <URL:ftp://ftp.python.org/pub/python/pc/>. |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
2199 |
|
f6e824b27032
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|
2200 7.3. Q. Is there an OS/2 version of Python? |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
2201 |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
2202 A. Yes, see the "pc" and "wpy" subdirectory of the distribution sites |
|
f6e824b27032
Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
2203 (see above). |
|
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Rewrite sections on GUI and DOS/Windows, various other small edits,
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|
2204 |
|
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|
2205 7.4. Q. Is there a VMS version of Python? |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
2206 |
| 2855 | 2207 A. Donn Cave <donn@cac.washington.edu> did a partial port. The |
| 2208 results of his efforts are on public display in | |
| 3018 | 2209 <<URL:ftp://ftp.python.org/pub/python/contrib/vms.tar.gz/>. Someone |
| 2210 else is working on a more complete port, for details watch the list. | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2211 |
|
4278
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|
2212 7.5. Q. What about IBM mainframes, or other non-UNIX platforms? |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2213 |
|
3023
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2214 A. I haven't heard about these, except I remember hearing about an |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2215 OS/9 port and a port to Vxworks (both operating systems for embedded |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2216 systems). If you're interested in any of this, go directly to the |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2217 newsgroup and ask there, you may find exactly what you need. For |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
changeset
|
2218 example, a port to MPE/iX 5.0 on HP3000 computers was just announced, |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
parents:
3018
diff
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|
2219 see <URL:http://www.allegro.com/software/>. |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2220 |
|
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|
2221 7.6. Q. Where are the source or Makefiles for the non-UNIX versions? |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2222 |
|
2661
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
parents:
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|
2223 A. The standard sources can (almost) be used. Additional sources can |
|
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
parents:
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|
2224 be found in the platform-specific subdirectories of the distribution. |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2225 |
|
4278
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|
2226 7.7. Q. What is the status and support for the non-UNIX versions? |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2227 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2228 A. I don't have access to most of these platforms, so in general I am |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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changeset
|
2229 dependent on material submitted by volunteers(*). However I strive to |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
1902
diff
changeset
|
2230 integrate all changes needed to get it to compile on a particular |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
1902
diff
changeset
|
2231 platform back into the standard sources, so porting of the next |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2232 version to the various non-UNIX platforms should be easy. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
2233 |
| 2048 | 2234 (*) For the Macintosh, that volunteer is me, with help from Jack |
| 2235 Jansen <jack@cwi.nl>. | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
2236 |
|
4278
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|
2237 7.8. Q. I have a PC version but it appears to be only a binary. |
| 1663 | 2238 Where's the library? |
| 1529 | 2239 |
| 2240 A. You still need to copy the files from the distribution directory | |
|
1547
0efa240b1dbc
At the release of 1.0.1
Guido van Rossum <guido@python.org>
parents:
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|
2241 "python/Lib" to your system. If you don't have the full distribution, |
|
2661
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2242 you can get the file lib<version>.tar.gz from most ftp sites carrying |
|
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2243 Python; this is a subset of the distribution containing just those |
|
2716
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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|
2244 files, e.g. <URL:ftp://ftp.python.org/pub/python/src/lib1.1.tar.gz>. |
| 1529 | 2245 |
|
1579
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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|
2246 Once you have installed the library, you need to point sys.path to it. |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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|
2247 Assuming the library is in C:\misc\python\lib, the following commands |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2248 will point your Python interpreter to it (note the doubled backslashes |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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diff
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|
2249 -- you can also use single forward slashes instead): |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2250 |
| 2048 | 2251 >>> import sys |
| 2252 >>> sys.path.insert(0, 'C:\\misc\\python\\lib') | |
| 2253 >>> | |
|
1579
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
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|
2254 |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2255 For a more permanent effect, set the environment variable PYTHONPATH, |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
2256 as follows (talking to a DOS prompt): |
|
021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
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diff
changeset
|
2257 |
| 2048 | 2258 C> SET PYTHONPATH=C:\misc\python\lib |
|
1579
021daabe69d8
Updated for existence of newsgroup and various misc things
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|
2259 |
|
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|
2260 7.9. Q. Where's the documentation for the Mac or PC version? |
| 1529 | 2261 |
|
2661
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
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changeset
|
2262 A. The documentation for the Unix version also applies to the Mac and |
|
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
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|
2263 PC versions. Where applicable, differences are indicated in the text. |
| 1529 | 2264 |
|
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|
2265 7.10. Q. The Mac (PC) version doesn't seem to have any facilities for |
|
1547
0efa240b1dbc
At the release of 1.0.1
Guido van Rossum <guido@python.org>
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|
2266 creating or editing programs apart from entering it interactively, and |
|
0efa240b1dbc
At the release of 1.0.1
Guido van Rossum <guido@python.org>
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|
2267 there seems to be no way to save code that was entered interactively. |
|
0efa240b1dbc
At the release of 1.0.1
Guido van Rossum <guido@python.org>
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changeset
|
2268 How do I create a Python program on the Mac (PC)? |
| 1529 | 2269 |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2270 A. Use an external editor. On the Mac, BBEdit seems to be a popular |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2271 no-frills text editor. I work like this: start the interpreter; edit |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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diff
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|
2272 a module file using BBedit; import and test it in the interpreter; |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2273 edit again in BBedit; then use the built-in function reload() to |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
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|
2274 re-read the imported module; etc. |
|
1579
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Updated for existence of newsgroup and various misc things
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|
2275 |
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Guido van Rossum <guido@python.org>
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2276 Regarding the same question for the PC, Kurt Wm. Hemr writes: "While |
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021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
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1547
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2277 anyone with a pulse could certainly figure out how to do the same on |
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021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
1547
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2278 MS-Windows, I would recommend the NotGNU Emacs clone for MS-Windows. |
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021daabe69d8
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Guido van Rossum <guido@python.org>
parents:
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2279 Not only can you easily resave and "reload()" from Python after making |
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021daabe69d8
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Guido van Rossum <guido@python.org>
parents:
1547
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2280 changes, but since WinNot auto-copies to the clipboard any text you |
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021daabe69d8
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Guido van Rossum <guido@python.org>
parents:
1547
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2281 select, you can simply select the entire procedure (function) which |
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021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
1547
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2282 you changed in WinNot, switch to QWPython, and shift-ins to reenter |
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021daabe69d8
Updated for existence of newsgroup and various misc things
Guido van Rossum <guido@python.org>
parents:
1547
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2283 the changed program unit." |