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| author | Guido van Rossum <guido@python.org> |
|---|---|
| date | Wed, 26 Jun 1996 19:30:01 +0000 |
| parents | fd573ac75947 |
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| rev | line source |
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| 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 |
| 1529 | 4 From: guido@cwi.nl (Guido van Rossum) |
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5 Reply-to: guido@cnri.reston.va.us (Guido van Rossum) |
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6 Expires: Wed, 1 Nov 1995 00:00:00 GMT |
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7 Supersedes: <DFMAv8.3Hp@cwi.nl> |
| 1529 | 8 Approved: news-answers-request@MIT.Edu |
| 9 | |
| 10 Archive-name: python-faq/part1 | |
| 2301 | 11 Submitted-by: Guido van Rossum <guido@cwi.nl> |
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12 Version: 1.29 |
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13 Last-modified: 11 October 1995 |
| 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 | |
| 2048 | 19 Copyright 1993-1995 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 22091 |
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28 U.S.A. |
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29 Email: <guido@python.org>, <guido@cnri.reston.va.us>, <guido@cwi.nl> |
| 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/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? |
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79 1.16. Q. What happened to Tim Peters (the author of python-mode.el, and many |
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80 entertaining and enlightening pieces of Python email)? |
| 1529 | 81 |
| 82 2. Python in the real world | |
| 83 2.1. Q. How many people are using Python? | |
| 84 2.2. Q. Have any significant projects been done in Python? | |
| 85 2.3. Q. Are there any commercial projects going on using Python? | |
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86 2.4. Q. How stable is Python? |
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87 2.5. Q. When will the next version be released? |
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88 2.6. Q. What new developments are expected for Python in the future? |
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89 2.7. Q. Is it reasonable to propose incompatible changes to Python? |
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90 2.8. Q. What is the future of Python? |
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91 2.9. Q. What is the PSA, anyway? |
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92 2.10. Q. How do I join the PSA? |
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93 2.11. Q. What are the benefits of joining the PSA? |
| 1529 | 94 |
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95 3. Building Python and Other Known Bugs |
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96 3.1. Q. Is there a test set? |
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97 3.2. Q. When running the test set, I get complaints about floating point |
| 1529 | 98 operations, but when playing with floating point operations I cannot |
| 99 find anything wrong with them. | |
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100 3.3. Q. Link errors after rerunning the configure script. |
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101 3.4. Q. The python interpreter complains about options passed to a |
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102 script (after the script name). |
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103 3.5. Q. When building on the SGI, make tries to run python to create |
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104 glmodule.c, but python hasn't been built or installed yet. |
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105 3.6. Q. Python built with gcc for the DEC Alpha doesn't work. |
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106 3.7. Q. I use VPATH but some targets are built in the source directory. |
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107 3.8. Q. Trouble building or linking with the GNU readline library. |
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108 3.9. Q. Trouble building Python on Linux. |
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109 3.10. Q. Trouble with prototypes on Ultrix. |
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110 3.11. Q. Trouble with posix.listdir on NeXTSTEP 3.2. |
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111 3.12. Q. Other trouble building Python on platform X. |
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112 3.13. Q. How to configure dynamic loading on Lixux. |
| 2855 | 113 3.14. Q. Under Solaris 2.x, using GCC, how do I use shared libraries? |
| 114 3.15. Q. Errors when linking with a shared library containing C++ code. | |
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115 3.16. Q. Tk menus or radiobuttons don't work properly in Python 1.2. |
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116 3.17. Q. I built with _tkintermodule.c enabled but get "Tkinter not found". |
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117 3.18. Q. I built with Tk 4.0 but Tkinter complains about the Tk version. |
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118 3.19. Q. Tk doesn't work right on DEC Alpha. |
| 1529 | 119 |
| 120 4. Programming in Python | |
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121 4.1. Q. Is there a source code level debugger with breakpoints, step, |
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122 etc.? |
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123 4.2. Q. Can I create an object class with some methods implemented in |
| 1529 | 124 C and others in Python (e.g. through inheritance)? (Also phrased as: |
| 125 Can I use a built-in type as base class?) | |
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126 4.3. Q. Is there a curses/termcap package for Python? |
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127 4.4. Q. Is there an equivalent to C's onexit() in Python? |
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128 4.5. Q. When I define a function nested inside another function, the |
| 1529 | 129 nested function seemingly can't access the local variables of the |
| 130 outer function. What is going on? How do I pass local data to a | |
| 131 nested function? | |
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132 4.6. Q. How do I iterate over a sequence in reverse order? |
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133 4.7. Q. My program is too slow. How do I speed it up? |
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134 4.8. Q. When I have imported a module, then edit it, and import it |
| 1529 | 135 again (into the same Python process), the changes don't seem to take |
| 136 place. What is going on? | |
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137 4.9. Q. How do I find the current module name? |
| 2048 | 138 4.10. Q. I have a module in which I want to execute some extra code |
| 139 when it is run as a script. How do I find out whether I am running as | |
| 140 a script? | |
| 141 4.11. Q. I try to run a program from the Demo directory but it fails | |
| 142 with ImportError: No module named ...; what gives? | |
| 1942 | 143 4.12. Q. I have successfully built Python with STDWIN but it can't |
| 144 find some modules (e.g. stdwinevents). | |
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145 4.13. Q. What GUI toolkits exist for Python? |
| 1942 | 146 4.14. Q. Are there any interfaces to database packages in Python? |
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147 4.15. Q. Is it possible to write obfuscated one-liners in Python? |
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148 4.16. Q. Is there an equivalent of C's "?:" ternary operator? |
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149 4.17. Q. My class defines __del__ but it is not called when I delete the |
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150 object. |
| 2048 | 151 4.18. Q. How do I change the shell environment for programs called |
| 152 using os.popen() or os.system()? Changing os.environ doesn't work. | |
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153 4.19. Q. What is a class? |
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154 4.20. Q. What is a method? |
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155 4.21. Q. What is self? |
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156 4.22. Q. What is a unbound method? |
| 2048 | 157 4.23. Q. How do I call a method defined in a base class from a derived |
| 158 class that overrides it? | |
| 159 4.24. Q. How do I call a method from a base class without using the | |
| 160 name of the base class? | |
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161 4.25. Q. How can I organize my code to make it easier to change the base |
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162 class? |
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163 4.26. Q. How can I find the methods or attributes of an object? |
| 1942 | 164 4.27. Q. I can't seem to use os.read() on a pipe created with os.popen(). |
| 165 4.28. Q. How can I create a stand-alone binary from a Python script? | |
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166 4.29. Q. What WWW tools are there for Python? |
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167 4.30. Q. How do I run a subprocess with pipes connected to both input |
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168 and output? |
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169 4.31. Q. How do I call a function if I have the arguments in a tuple? |
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170 4.32. Q. How do I enable font-lock-mode for Python in Emacs? |
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171 4.33. Q. Is there an inverse to the format operator (a la C's scanf())? |
| 1529 | 172 |
| 173 5. Extending Python | |
| 174 5.1. Q. Can I create my own functions in C? | |
| 175 5.2. Q. Can I create my own functions in C++? | |
| 1663 | 176 5.3. Q. How can I execute arbitrary Python statements from C? |
| 177 5.4. Q. How can I evaluate an arbitrary Python expression from C? | |
| 178 5.5. Q. How do I extract C values from a Python object? | |
| 179 5.6. Q. How do I use mkvalue() to create a tuple of arbitrary length? | |
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180 5.7. Q. What happened to mktuple(), featured in an example in the |
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181 Extensions manual? |
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182 5.8. Q. How do I call an object's method from C? |
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183 5.9. Q. How do I catch the output from print_error()? |
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184 5.10. Q. How do I access a module written in Python from C? |
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185 5.11. Q. How do I interface to C++ objects from Python? |
| 1529 | 186 |
| 187 6. Python's design | |
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188 6.1. Q. Why isn't there a generic copying operation for objects in Python? |
| 1529 | 189 6.2. Q. Why isn't there a generic way to implement persistent objects |
| 190 in Python? (Persistent == automatically saved to and restored from | |
| 191 disk.) | |
| 192 6.3. Q. Why isn't there a switch or case statement in Python? | |
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193 6.4. Q. Why does Python use indentation for grouping of statements? |
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194 6.5. Q. Why are Python strings immutable? |
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195 6.6. Q. Why don't strings have methods like index() or sort(), like |
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196 lists? |
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197 6.7. Q. Why does Python use methods for some functionality |
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198 (e.g. list.index()) but functions for other (e.g. len(list))? |
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199 6.8. Q. Why can't I derive a class from built-in types (e.g. lists or |
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200 files)? |
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201 6.9. Q. Why must 'self' be declared and used explicitly in method |
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202 definitions and calls? |
| 1942 | 203 6.10. Q. Can't you emulate threads in the interpreter instead of |
| 204 relying on an OS-specific thread implementation? | |
| 205 6.11. Q. Why can't lambda forms contain statements? | |
| 206 6.12. Q. Why is there no more efficient way of iterating over a dictionary | |
| 207 than first constructing the list of keys()? | |
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208 6.13. Q. Can Python be compiled to machine code, C or some other language? |
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209 6.14. Q. Why doesn't Python use proper garbage collection? |
| 1529 | 210 |
| 211 7. Using Python on non-UNIX platforms | |
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212 7.1. Q. Is there a Mac version of Python? |
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213 7.2. Q. Is there a DOS version of Python? |
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214 7.3. Q. Is there a Windows 3.1(1) version of Python? |
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215 7.4. Q. Is there a Windows NT version of Python? |
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216 7.5. Q. Is there a Windows 95 version of Python? |
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217 7.6. Q. Is there an OS/2 version of Python? |
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218 7.7. Q. Is there a VMS version of Python? |
| 3018 | 219 7.8. Q. What about IBM mainframes, or other non-UNIX platforms? |
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220 7.9. Q. Where are the source or Makefiles for the non-UNIX versions? |
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221 7.10. Q. What is the status and support for the non-UNIX versions? |
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222 7.11. Q. I have a PC version but it appears to be only a binary. |
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223 Where's the library? |
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224 7.12. Q. Where's the documentation for the Mac or PC version? |
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225 7.13. Q. The Mac (PC) version doesn't seem to have any facilities for |
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226 creating or editing programs apart from entering it interactively, and |
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227 there seems to be no way to save code that was entered interactively. |
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228 How do I create a Python program on the Mac (PC)? |
| 1529 | 229 |
| 230 To find a particular question, search for the question number followed | |
| 231 by a dot, a space, and a Q at the beginning of a line (e.g. to find | |
| 232 question 4.2 in vi, type /^4\.2\. Q/). | |
| 233 | |
| 234 | |
| 235 1. General information and availability | |
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236 ======================================= |
| 1529 | 237 |
| 238 1.1. Q. What is Python? | |
| 239 | |
| 240 A. Python is an interpreted, interactive, object-oriented programming | |
| 241 language. It incorporates modules, exceptions, dynamic typing, very | |
| 242 high level dynamic data types, and classes. Python combines | |
| 243 remarkable power with very clear syntax. It has interfaces to many | |
| 244 system calls and libraries, as well as to various window systems, and | |
| 245 is extensible in C or C++. It is also usable as an extension language | |
| 246 for applications that need a programmable interface. Finally, Python | |
| 2048 | 247 is portable: it runs on many brands of UNIX, on the Mac, and on PCs |
| 248 under MS-DOS, Windows, Windows NT, and OS/2. | |
| 1529 | 249 |
| 250 To find out more, the best thing to do is to start reading the | |
| 251 tutorial from the documentation set (see a few questions further | |
| 252 down). | |
| 253 | |
| 254 1.2. Q. Why is it called Python? | |
| 255 | |
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256 A. Apart from being a computer scientist, I'm also a fan of "Monty |
| 1529 | 257 Python's Flying Circus" (a BBC comedy series from the seventies, in |
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258 the -- unlikely -- case you didn't know). It occurred to me one day |
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259 that I needed a name that was short, unique, and slightly mysterious. |
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260 And I happened to be reading some scripts from the series at the |
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261 time... So then I decided to call my language Python. But Python is |
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262 not a joke. And don't you associate it with dangerous reptiles |
| 2048 | 263 either! (If you need an icon, use an image of the 16-ton weight from |
| 264 the TV series or of a can of SPAM :-) | |
| 1529 | 265 |
| 266 1.3. Q. How do I obtain a copy of the Python source? | |
| 267 | |
| 2048 | 268 A. The latest complete Python source distribution is always available |
| 269 by anonymous ftp, e.g. | |
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270 <URL:ftp://ftp.python.org/pub/python/src/python1.2.tar.gz>. It is a |
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271 gzipped tar file containing the complete C source, LaTeX |
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272 documentation, Python library modules, example programs, and several |
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273 useful pieces of freely distributable software. This will compile and |
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274 run out of the box on most UNIX platforms. (See section 7 for |
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275 non-UNIX information.) |
| 2048 | 276 |
| 277 Occasionally a set of patches is issued which has to be applied using | |
| 278 the patch program. These patches are placed in the same directory, | |
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279 e.g. <URL:ftp://ftp.python.org/pub/python/src/patch1.1.1>. (At the time |
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280 of writing, no patches exist for 1.2.) |
| 2048 | 281 |
| 282 An index of said ftp directory can be found in the file INDEX. An | |
| 283 HTML version of the index can be found in the file index.html, | |
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284 <URL:ftp://ftp.python.org/pub/python/index.html>. |
| 1529 | 285 |
| 286 1.4. Q. How do I get documentation on Python? | |
| 287 | |
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288 A. The LaTeX source for the documentation is part of the source |
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289 distribution. If you don't have LaTeX, the latest Python |
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290 documentation set is always available by anonymous ftp, e.g. |
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291 <URL:ftp://ftp.python.org/pub/python/doc/postscript.tar.gz>. It is a |
| 2048 | 292 gzipped tar file containing PostScript files of the reference manual, |
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293 the library manual, and the tutorial. Note that the library manual is |
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294 the most important one of the set, as much of Python's power stems |
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295 from the standard or built-in types, functions and modules, all of |
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296 which are described here. PostScript for a high-level description of |
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297 Python is in the file nluug-paper.ps (a separate file on the ftp |
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298 site). |
| 1529 | 299 |
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300 1.5. Q. Are there other ftp sites that mirror the Python distribution? |
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301 |
| 2048 | 302 A. The following anonymous ftp sites keep mirrors of the Python |
| 303 distribution: | |
| 1529 | 304 |
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305 USA: |
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306 |
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307 <URL:ftp://ftp.python.org/pub/python/> |
| 2048 | 308 <URL:ftp://gatekeeper.dec.com/pub/plan/python/> |
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309 <URL:ftp://ftp.uu.net/languages/python/> |
| 2048 | 310 <URL:ftp://ftp.wustl.edu/graphics/graphics/sgi-stuff/python/> |
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311 <URL:ftp://ftp.sterling.com/programming/languages/python/> |
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312 <URL:ftp://uiarchive.cso.uiuc.edu/pub/lang/python/> |
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313 <URL:ftp://ftp.pht.com/mirrors/python/python/> |
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314 |
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315 Europe: |
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316 |
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317 <URL:ftp://ftp.cwi.nl/pub/python/> |
| 2048 | 318 <URL:ftp://ftp.funet.fi/pub/languages/python/> |
| 319 <URL:ftp://ftp.sunet.se/pub/lang/python/> | |
| 2855 | 320 <URL:ftp://unix.hensa.ac.uk/mirrors/uunet/languages/python/> |
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321 <URL:ftp://ftp.ibp.fr/pub/python/> |
| 2855 | 322 <URL:ftp://ftp.switch.ch/software/sources/python/> |
| 323 <URL:ftp://ftp.informatik.tu-muenchen.de/pub/comp/programming/languages/python/> | |
| 1529 | 324 |
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325 Australia: |
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326 |
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327 <URL:ftp://ftp.dstc.edu.au/pub/python/> |
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328 |
| 2048 | 329 Or try archie on the string "python". |
| 1529 | 330 |
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331 1.6. Q. Is there a newsgroup or mailing list devoted to Python? |
| 1529 | 332 |
| 2048 | 333 A. There is a newsgroup, comp.lang.python <URL:news:comp.lang.python>, |
| 334 and a mailing list. The newsgroup and mailing list are gatewayed into | |
| 335 each other -- if you can read news it's unnecessary to subscribe to | |
| 336 the mailing list. Send e-mail to <python-list-request@cwi.nl> to | |
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337 (un)subscribe to the mailing list. Hypermail archives of (nearly) |
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338 everything posted to the mailing list (and thus the newsgroup) are |
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339 available on our WWW server, |
| 2048 | 340 <URL:http://www.cwi.nl/~guido/hypermail/index.html>. The raw archives |
| 341 are also available by ftp, e.g. | |
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342 <URL:ftp://ftp.python.org/pub/python/mail/mailinglist.gz>. The |
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343 uncompressed versions of these files can be read with the standard |
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344 UNIX Mail program ("Mail -f file") or with nn ("nn file"). To read |
| 3018 | 345 them using MH, you could use "inc -file file". (The archival service |
| 346 has stopped archiving new articles around the end of April 1995. I | |
| 347 hope to revive it on the PSA server www.python.org sometime in the | |
| 348 future.) | |
| 1529 | 349 |
| 2048 | 350 1.7. Q. Is there a WWW page devoted to Python? |
| 351 | |
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352 A. Yes, <URL:http://www.python.org/> is the official Python home page. |
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353 At the time of writing, this page is not yet completely operational; |
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354 you may have a look at the old Python home page: |
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355 <URL:http://www.cwi.nl/~guido/Python.html> or at the U.S. copy: |
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356 <URL:http://www.python.org/~guido/Python.html>. |
| 2048 | 357 |
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358 1.8. Q. Is the Python documentation available on the WWW? |
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359 |
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360 A. Yes, see <URL:http://www.python.org/> (Python's home page). It |
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361 contains pointers to hypertext versions of the whole documentation set |
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362 (as hypertext, not just PostScript). |
| 1529 | 363 |
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364 If you wish to browse this collection of HTML files on your own |
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365 machine, it is available bundled up by anonymous ftp, |
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366 e.g. <URL:ftp://ftp.python.org/pub/python/doc/html.tar.gz>. |
| 1529 | 367 |
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368 An Emacs-INFO set containing the library manual is also available by |
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369 ftp, e.g. <URL:ftp://ftp.python.org/pub/python/doc/lib-info.tar.gz>. |
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370 |
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371 1.9. Q. Is there a book on Python, or will there be one out soon? |
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372 |
| 2855 | 373 A. Mark Lutz is writing a Python book for O'Reilly and Associates, to |
| 374 be published early 1996. See the outline (in PostScript): | |
| 375 <URL:http://www.python.org/workshops/1995-05/outlinep.eps>. | |
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376 |
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377 1.10. Q. Are there any published articles about Python that I can quote? |
| 1529 | 378 |
| 379 A. So far the only refereed and published article that describes | |
| 380 Python in some detail is: | |
| 381 | |
| 382 Guido van Rossum and Jelke de Boer, "Interactively Testing Remote | |
| 383 Servers Using the Python Programming Language", CWI Quarterly, Volume | |
| 384 4, Issue 4 (December 1991), Amsterdam, pp 283-303. | |
| 385 | |
| 386 LaTeX source for this paper is available as part of the Python source | |
| 387 distribution. | |
| 388 | |
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389 See also the next section (supposedly Aaron Watters' paper has been |
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390 refereed). |
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391 |
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392 1.11. Q. Are there short introductory papers or talks on Python? |
| 2048 | 393 |
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394 A. A recent, very entertaining introduction to Python is the tutorial by |
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395 Aaron Watters in UnixWorld Online: |
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396 |
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397 Aaron R. Watters: "The What, Why, Who, and Where of Python", |
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398 <URL:http://www.wcmh.com/uworld/archives/95/tutorial/005.html> |
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399 |
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400 An olded paper is: |
| 1529 | 401 |
| 402 Guido van Rossum, "An Introduction to Python for UNIX/C | |
| 403 Programmers", in the proceedings of the NLUUG najaarsconferentie | |
| 1942 | 404 1993 (dutch UNIX users group meeting November 1993). |
| 2048 | 405 |
| 1529 | 406 PostScript for this paper and for the slides used for the accompanying |
| 2048 | 407 presentation is available by ftp as |
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408 <URL:ftp://ftp.python.org/pub/python/doc/nluug-paper.ps> and |
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409 <URL:ftp://ftp.python.org/pub/python/doc/nluug-slides.ps>, respectively. |
| 1529 | 410 |
| 2048 | 411 Slides for a talk on Python that I gave at the Usenix Symposium on |
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412 Very High Level Languages in Santa Fe, NM, USA in October 1994 are |
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413 available as <URL:ftp://ftp.python.org/pub/python/doc/vhll-slides.ps>. |
| 2048 | 414 |
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415 1.12. Q. How does the Python version numbering scheme work? |
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416 |
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417 A. Python versions are numbered A.B.C or A.B. A is the major version |
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418 number -- it is only incremented for major changes in functionality or |
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419 source structure. B is the minor version number, incremented for less |
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420 earth-shattering changes to a release. C is the patchlevel -- it is |
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421 incremented for each new patch release. Not all releases have patch |
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422 releases. Note that in the past, patches have added significant |
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423 changes; in fact the changeover from 0.9.9 to 1.0.0 was the first time |
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424 that either A or B changed! |
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425 |
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426 Beta versions have an additional suffix of "-beta-N" for some small |
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427 number N. Note that (for instance) all versions labeled 1.2-beta-N |
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428 *precede* the actual release of 1.2. 1.3b1 is short for 1.3-beta-1. |
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429 |
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430 1.13. Q. How do I get a beta test version of Python? |
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431 |
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432 A. If there are any beta releases, they are published in the normal |
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433 source directory (e.g. <URL:ftp://ftp.python.org/pub/python/src/>). |
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434 |
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435 1.14. Q. Are there copyright restrictions on the use of Python? |
| 1663 | 436 |
| 437 A. Hardly. You can do anything you want with the source, as long as | |
| 2048 | 438 you leave the copyrights in, and display those copyrights in any |
| 439 documentation about Python that you produce. Also, don't use the | |
| 440 author's institute's name in publicity without prior written | |
| 441 permission, and don't hold them responsible for anything (read the | |
| 442 actual copyright for a precise legal wording). | |
| 443 | |
| 444 In particular, if you honor the copyright rules, it's OK to use Python | |
| 445 for commercial use, to sell copies of Python in source or binary form, | |
| 446 or to sell products that enhance Python or incorporate Python (or part | |
| 447 of it) in some form. I would still like to know about all commercial | |
| 448 use of Python! | |
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449 |
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450 1.15. Q. Why was Python created in the first place? |
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451 |
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452 A. Here's a *very* brief summary of what got me started: |
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453 |
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454 - I had extensive experience with implementing an interpreted language |
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455 in the ABC group at CWI, and from working with this group I had |
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456 learned a lot about language design. This is the origin of many |
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457 Python features, including the use of indentation for statement |
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458 grouping and the inclusion of very-high-level data types (although the |
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459 details are all different in Python). |
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460 |
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461 - I had a number of gripes about the ABC language, but also liked many |
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462 of its features. It was impossible to extend the ABC language (or its |
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463 implementation) to remedy my complaints -- in fact its lack of |
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464 extensibility was one of its biggest problems. |
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465 |
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466 - I had some experience with using Modula-2+ and talked with the |
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467 designers of Modula-3 (and read the M3 report). M3 is the origin of |
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468 the syntax and semantics used for exceptions, and some other Python |
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469 features. |
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470 |
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471 - I was working in the Amoeba distributed operating system group at |
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472 CWI. We needed a better way to do system administration than by |
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473 writing either C programs or Bourne shell scripts, since Amoeba had |
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474 its own system call interface which wasn't easily accessible from the |
| 3018 | 475 Bourne shell. My experience with error handling in Amoeba made me |
| 476 acutely aware of the importance of exceptions as a programming | |
| 477 language feature. | |
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478 |
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479 - It occurred to me that a scripting language with a syntax like ABC |
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480 but with access to the Amoeba system calls would fill the need. I |
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481 realized that it would be foolish to write an Amoeba-specific |
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482 language, so I decided that I needed a language that was generally |
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483 extensible. |
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484 |
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485 - During the 1989 Christmas holidays, I had a lot of time on my hand, |
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486 so I decided to give it a try. During the next year, while still |
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487 mostly working on it in my own time, Python was used in the Amoeba |
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488 project with increasing success, and the feedback from colleagues made |
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489 me add many early improvements. |
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490 |
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491 - In February 1991, after just over a year of development, I decided |
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492 to post to USENET. The rest is in the Misc/HISTORY file. |
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493 |
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494 1.16. Q. What happened to Tim Peters (the author of python-mode.el, and many |
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495 entertaining and enlightening pieces of Python email)? |
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496 |
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497 A. He worked at KSR (Kendall Square Research, a start-up building a |
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498 new kind of massively parallel processor). When KSR folded down a |
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499 couple of years ago, Tim lost his email access. He hasn't surfaced |
|
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500 on the net since then. |
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501 |
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502 Missing-him-too-ly yours... |
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503 |
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504 PS: support for Python's Emacs mode (Misc/python-mode.el in the |
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505 distribution) has been taken up by Barry Warsaw. Questions about it |
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506 should be mailed to <python-mode@python.org>. |
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507 |
| 1529 | 508 |
| 509 2. Python in the real world | |
| 510 =========================== | |
| 511 | |
| 512 2.1. Q. How many people are using Python? | |
| 513 | |
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514 A. I don't know, but the maximum number of simultaneous subscriptions |
|
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515 to the Python mailing list before it was gatewayed into the newsgroup |
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516 was about 180 (several of which were local redistribution lists). I |
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517 believe that many active Python users don't bother to subscribe to the |
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518 list, and now that there's a newsgroup the mailing list subscription |
| 1663 | 519 is even less meaningful. I see new names on the newsgroup all the |
| 520 time and my best guess is that there are currently at least several | |
| 521 thousands of users. | |
| 1529 | 522 |
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523 Another statistic is the number of accesses to the Python WWW server. |
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524 Have a look at <URL:http://www.python.org/stats/>. |
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525 |
| 1529 | 526 2.2. Q. Have any significant projects been done in Python? |
| 527 | |
| 528 A. Here at CWI (the home of Python), we have written a 20,000 line | |
| 529 authoring environment for transportable hypermedia presentations, a | |
|
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530 5,000 line multimedia teleconferencing tool, as well as many many |
|
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531 smaller programs. |
| 1529 | 532 |
| 533 The University of Virginia uses Python to control a virtual reality | |
| 534 engine. Contact: Matt Conway <conway@virginia.edu>. | |
| 535 | |
| 2048 | 536 The ILU project at Xerox PARC can generate Python glue for ILU |
| 537 interfaces. See <URL:ftp://ftp.parc.xerox.com/pub/ilu/ilu.html>. | |
| 538 | |
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539 The University of California, Irvine uses a student administration |
|
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540 system called TELE-Vision written entirely in Python. Contact: Ray |
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541 Price <rlprice@uci.edu>. |
|
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542 |
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543 See also the next question. |
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544 |
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545 If you have done a significant project in Python that you'd like to be |
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546 included in the list above, send me email! |
| 1529 | 547 |
| 548 2.3. Q. Are there any commercial projects going on using Python? | |
| 549 | |
| 550 A. Several companies have revealed to me that they are planning or | |
|
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551 considering use of Python in a future product. |
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552 |
| 3018 | 553 Sunrise Software has a product out using Python -- they use Python |
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554 for a GUI management application and an SNMP network management |
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555 application. Contact: <info@sunrise.com>. |
| 1529 | 556 |
| 2048 | 557 Infoseek uses Python to implement their commercial WWW information |
| 558 retrieval service <URL:http://www.infoseek.com/>. Contact: | |
| 559 <info@infoseek.com>. | |
|
1784
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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560 |
| 2048 | 561 Paul Everitt of Connecting Minds is planning a Lotus Notes gateway. |
| 562 Contact: <Paul.Everitt@cminds.com>. Or see their WWW server | |
| 563 <URL:http://www.cminds.com/>. | |
| 564 | |
|
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565 KaPRE in Boulder, CO is using Python for on-site customization of C++ |
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566 applications, rapid-prototyping/development, |
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567 language-based-components, and possibly more. This is pretty solid: |
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568 Python's being shipped with their tool-set now, to beta sites. |
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569 Contact: <lutz@KaPRE.COM> (Mark Lutz). |
|
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570 |
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571 Individuals at many other companies are using Python for internal |
|
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572 development or for as yet unannounced products (witness their |
|
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573 contributions to the Python mailing list or newsgroup). |
| 1529 | 574 |
|
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575 SGI has advertised in the Python list looking for Python programmers |
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576 for a project involving interactive television. |
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577 |
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578 See also the workshop minutes at |
|
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579 <URL:http://www.python.org/workshops/> -- in general the WWW server is |
|
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580 more up to date than the FAQ for these issues. |
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581 |
| 1529 | 582 Python has also been elected as an extension language by MADE, a |
| 583 consortium supported by the European Committee's ESPRIT program and | |
| 584 consisting of Bull, CWI and some other European companies. Contact: | |
| 585 Ivan Herman <ivan@cwi.nl>. | |
| 586 | |
|
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587 If you'd like to be included in the list above, send me email! |
|
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588 |
|
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589 2.4. Q. How stable is Python? |
| 1529 | 590 |
|
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591 A. Very stable. While the current version number would suggest it is |
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592 in the early stages of development, in fact new, stable releases |
|
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593 (numbered 0.9.x through 1.3) have been coming out roughly every 3 to |
| 2048 | 594 6 months for the past four years. |
|
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595 |
|
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596 2.5. Q. When will the next version be released? |
|
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597 |
|
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598 A. Version 1.3 is being released on 13 October 1995. It is too early |
|
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599 to predict when the next release will be necessary, but you can expect |
|
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600 something awesome within half a year! |
|
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601 |
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602 2.6. Q. What new developments are expected for Python in the future? |
| 1529 | 603 |
|
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604 A. See my Work-In-Progress web page, currently at |
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605 <URL:http://www.python.org:~guido/WIP.html>, and the pages for the |
|
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606 Second Python Workshop (best reached via the Python home page, |
|
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607 <URL:http://www.python.org/>). Also follow the newsgroup discussions! |
| 2048 | 608 |
|
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609 2.7. Q. Is it reasonable to propose incompatible changes to Python? |
|
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610 |
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611 A. In general, no. There are already millions of lines of Python code |
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612 around the world, so any changes in the language that invalidates more |
|
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613 than a very small fraction of existing programs has to be frowned |
|
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614 upon. Even if you can provide a conversion program, there still is |
|
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615 the problem of updating all documentation. Providing a gradual |
|
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616 upgrade path is the only way if a feature has to be changed. |
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617 |
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618 2.8. Q. What is the future of Python? |
| 1529 | 619 |
|
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620 A. If I knew, I'd be rich :-) |
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621 |
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622 Seriously, the formation of the PSA (Pyton Software Activity, see |
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623 <URL:http://www.python.org/psa/>) ensures some kind of support even in |
|
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624 the (unlikely! event that I'd be hit by a bus (actually, here in the |
|
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625 US, a car accident would be more likely :-), were to join a nunnery, |
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626 or would be head-hunted. A large number of Python users have become |
|
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627 experts at Python programming as well as maintenance of the |
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628 implementation, and would easily fill the vacuum created by my |
|
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629 disappearance. |
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630 |
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631 In the mean time, I have no plans to disappear -- rather, I am |
|
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632 committed to improving Python, and my current benefactor, CNRI (see |
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633 <URL:http://www.cnri.reston.va.us>) is just as committed to continue |
|
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634 its support of Python and the PSA. In fact, we have great plans for |
|
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635 Python -- we just can't tell yet! |
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636 |
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637 2.9. Q. What is the PSA, anyway? |
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638 |
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639 A. The Python Software Activity <URL:http://www.python.org/psa/> was |
|
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640 created by a number of Python aficionados who want Python to be more |
|
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641 than the product and responsibility of a single individual. It has |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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|
642 found a home at CNRI <URL:http://www.cnri.reston.va.us>. Anybody who |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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643 wishes Python well should join the PSA. |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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|
644 |
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+aaron watters, +PSA, +GC, -lance, -beta
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|
645 2.10. Q. How do I join the PSA? |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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646 |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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647 A. The full scoop is available on the web, see |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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|
648 <URL:http://www.python.org/psa/Joining.html>. Summary: send a check |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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|
649 of at least $50 to CNRI/PSA, 1895 Preston White Drive, Suite 100, in |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
parents:
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diff
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|
650 Reston, VA 22091. Full-time students pay $25. Companies can join for |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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651 a mere $500. |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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652 |
|
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+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
parents:
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|
653 2.11. Q. What are the benefits of joining the PSA? |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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parents:
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|
654 |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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|
655 A. Like National Public Radio, if not enough people join, Python will |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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656 wither. Your name will be mentioned on the PSA's web server. |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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|
657 Workshops organized by the PSA <URL:http://www.python.org/workshops/> |
|
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+aaron watters, +PSA, +GC, -lance, -beta
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|
658 are only accessible to PSA members (you can join at the door). The |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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parents:
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|
659 PSA is working on additional benefits, such as reduced prices for |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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parents:
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|
660 books and software, and early access to beta versions of Python. |
|
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
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|
661 |
|
3023
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
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|
662 |
|
87847228b158
several new questions, 1.3 beta mentioned
Guido van Rossum <guido@python.org>
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|
663 3. Building Python and Other Known Bugs |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
664 ======================================= |
| 1529 | 665 |
|
1547
0efa240b1dbc
At the release of 1.0.1
Guido van Rossum <guido@python.org>
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|
666 3.1. Q. Is there a test set? |
| 1529 | 667 |
| 668 A. Yes, simply do "import testall" (or "import autotest" if you aren't | |
| 669 interested in the output). The standard modules whose name begins | |
| 670 with "test" together comprise the test. The test set doesn't test | |
| 671 *all* features of Python but it goes a long way to confirm that a new | |
| 672 port is actually working. The Makefile contains an entry "make test" | |
| 2048 | 673 which runs the autotest module. NOTE: if "make test" fails, run the |
| 674 tests manually ("import testall") to see what goes wrong before | |
| 675 reporting the error. | |
| 1529 | 676 |
|
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At the release of 1.0.1
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diff
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|
677 3.2. Q. When running the test set, I get complaints about floating point |
| 1529 | 678 operations, but when playing with floating point operations I cannot |
| 679 find anything wrong with them. | |
| 680 | |
| 681 A. The test set makes occasional unwarranted assumptions about the | |
| 682 semantics of C floating point operations. Until someone donates a | |
| 683 better floating point test set, you will have to comment out the | |
| 684 offending floating point tests and execute similar tests manually. | |
| 685 | |
|
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next version; python.org changes
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686 3.3. Q. Link errors after rerunning the configure script. |
|
1541
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
687 |
|
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Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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|
688 A. It is generally necessary to run "make clean" after a configuration |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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|
689 change. |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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|
690 |
|
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19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
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|
691 3.4. Q. The python interpreter complains about options passed to a |
|
1541
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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parents:
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|
692 script (after the script name). |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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parents:
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|
693 |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
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parents:
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|
694 A. You are probably linking with GNU getopt, e.g. through -liberty. |
|
1784
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
Guido van Rossum <guido@python.org>
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|
695 Don't. The reason for the complaint is that GNU getopt, unlike System |
|
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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|
696 V getopt and other getopt implementations, doesn't consider a |
|
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
Guido van Rossum <guido@python.org>
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|
697 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
Guido van Rossum <guido@python.org>
parents:
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|
698 fix for scripts is to add "--" to the interpreter, like this: |
|
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
Guido van Rossum <guido@python.org>
parents:
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|
699 |
| 2048 | 700 #! /usr/local/bin/python -- |
|
1784
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
Guido van Rossum <guido@python.org>
parents:
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|
701 |
|
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
Guido van Rossum <guido@python.org>
parents:
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|
702 You can also use this interactively: |
|
a3f199e8bac6
1.12 -- new address for fu-berlin mirror, infoseek uses python, more
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|
703 |
| 2048 | 704 python -- script.py [options] |
| 705 | |
| 706 Note that a working getopt implementation is provided in the Python | |
| 707 distribution (in Python/getopt.c) but not automatically used. | |
|
1541
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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|
708 |
|
2716
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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|
709 3.5. Q. When building on the SGI, make tries to run python to create |
|
1541
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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|
710 glmodule.c, but python hasn't been built or installed yet. |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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diff
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|
711 |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
1535
diff
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|
712 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...
Guido van Rossum <guido@python.org>
parents:
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|
713 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...
Guido van Rossum <guido@python.org>
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|
714 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...
Guido van Rossum <guido@python.org>
parents:
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|
715 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...
Guido van Rossum <guido@python.org>
parents:
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|
716 Makefile" in the Modules subdirectory (or just run "make" at the |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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|
717 toplevel). |
|
630e03109c63
Released version 1.4; out after 1.0.0 is released...
Guido van Rossum <guido@python.org>
parents:
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|
718 |
|
2716
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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|
719 3.6. Q. Python built with gcc for the DEC Alpha doesn't work. |
|
1740
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
Guido van Rossum <guido@python.org>
parents:
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diff
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|
720 |
|
2526
d1123b10cf23
removed GPL mumbo jumbo
Guido van Rossum <guido@python.org>
parents:
2301
diff
changeset
|
721 People have reported problems with gcc 2.5.8 up to 2.6.3. The DEC |
|
d1123b10cf23
removed GPL mumbo jumbo
Guido van Rossum <guido@python.org>
parents:
2301
diff
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|
722 OSF/1 cc compiler does not have these problems so it's likely a gcc |
|
2661
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
parents:
2660
diff
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|
723 bug. The latest news is that this has been fixed in Python 1.2 by a |
|
b4fd48e3a3b8
changed path references
Guido van Rossum <guido@python.org>
parents:
2660
diff
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|
724 source change (I gave up waiting for a fixed gcc). |
|
1740
e95b0701c8b5
Version 1.11 -- added several new answers on design questions
Guido van Rossum <guido@python.org>
parents:
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|
725 |
|
2716
19b1195a3af8
next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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changeset
|
726 3.7. 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).
Guido van Rossum <guido@python.org>
parents:
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|
727 |
|
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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|
728 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).
Guido van Rossum <guido@python.org>
parents:
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|
729 source directory, it is created there instead of in the build |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
730 directory. This is usually because you have previously built without |
|
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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|
731 VPATH. Try running "make clobber" in the source directory. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
732 |
|
2716
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next version; python.org changes
Guido van Rossum <guido@python.org>
parents:
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changeset
|
733 3.8. Q. Trouble building or linking with the GNU readline library. |
|
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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|
734 |
|
2660
4eb6ddb9e961
Some more changes for 1.2
Guido van Rossum <guido@python.org>
parents:
2526
diff
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|
735 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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diff
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|
736 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
737 - You can use the GNU readline library to improve the interactive user |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
738 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
|
739 calling python interactively. You need to configure and build the GNU |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
740 readline library before running the configure script. Its sources are |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
741 no longer distributed with Python; you can ftp them from any GNU |
| 2048 | 742 mirror site, or from its home site |
| 743 <URL:ftp://slc2.ins.cwru.edu/pub/dist/readline-2.0.tar.gz> (or a | |
| 744 higher version number -- using version 1.x is not recommended). Pass | |
| 745 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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|
746 DIRECTORY is the absolute pathname of the directory where you've built |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
747 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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|
748 library: |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
749 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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diff
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|
750 - 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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|
751 to rldefs.h: |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
752 |
| 2048 | 753 #ifndef sigmask |
| 754 #define sigmask(sig) (1L << ((sig)-1)) | |
| 755 #endif | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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parents:
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|
756 |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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diff
changeset
|
757 - 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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parents:
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diff
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|
758 top of several source files, and if you use the VPATH feature, you |
|
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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|
759 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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|
760 Makefile for several values of foo. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
761 |
|
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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|
762 - The readline library requires use of the termcap library. A |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
Guido van Rossum <guido@python.org>
parents:
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|
763 known problem with this is that it contains entry points which |
| 1942 | 764 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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|
765 conflict can be solved (and will be, in the next release of |
| 1942 | 766 STDWIN) by adding a line saying '#define werase w_erase' to the |
| 767 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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|
768 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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diff
changeset
|
769 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>
parents:
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diff
changeset
|
770 |
|
2660
4eb6ddb9e961
Some more changes for 1.2
Guido van Rossum <guido@python.org>
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|
771 - Check the newsgroup gnu.bash.bug <URL:news:gnu.bash.bug> for |
|
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772 specific problems with the readline library (I don't read this group |
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773 but I've been told that it is the place for readline bugs). |
|
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|
774 |
|
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775 3.9. Q. Trouble building Python on Linux. |
|
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776 |
|
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777 A. If you're building Python 1.2, Slackware 2.2 has a buggy bash |
|
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778 (version 1.14.3) which breaks a sed script that is used to build |
|
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779 Modules/Makefile. Replace /bin/sh with /bin/ash in both makesetup and |
|
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780 Makefile.pre.in. |
|
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781 |
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782 In 1.1 and 1.1.1, there's a bug in the reference counting logic of |
|
2526
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783 ternary pow() which is only tripped by very picky mallocs, like the |
|
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784 GNU malloc on Linux. This has been fixed in 1.2. To continue the |
|
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785 tests in 1.1(.1), just disable the tests of pow() with three arguments |
|
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|
786 from Lib/test/test_b2.py. |
| 2048 | 787 |
|
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788 Apart from this, Python builds and runs fine on most Linux versions |
|
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789 (if you run into trouble on an old Linux version, consider upgrading). |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
790 |
|
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|
791 3.10. Q. Trouble with prototypes on Ultrix. |
|
1957
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add warning about ultrix cc
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|
792 |
|
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add warning about ultrix cc
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793 A. Ultrix cc seems broken -- use gcc, or edit config.h to #undef |
|
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add warning about ultrix cc
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|
794 HAVE_PROTOTYPES. |
|
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|
795 |
|
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|
796 3.11. Q. Trouble with posix.listdir on NeXTSTEP 3.2. |
| 2012 | 797 |
| 2855 | 798 A. (This often manifests itself as a weird error from the |
| 799 compileall.py script run by "make libinstall".) | |
| 2012 | 800 |
| 2855 | 801 Don't use gcc, use the Next C compiler (cc). Even though it is |
| 802 derived from (an old version of) gcc, its interpretation of the | |
| 803 "-posix" switch is different; in this particular case, cc is right and | |
| 804 gcc is wrong. | |
| 2012 | 805 |
|
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806 3.12. Q. Other trouble building Python on platform X. |
|
1533
995a8ef4a5c0
Changes for release of 1.0.0
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|
807 |
|
2208
c68a0113b75a
intermediate version -- why not...
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|
808 A. Please email the details to <guido@cwi.nl> and I'll look into it. |
|
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809 Please provide as many details as possible. In particular, if you |
|
c68a0113b75a
intermediate version -- why not...
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|
810 don't tell me what type of computer and what operating system (and |
|
c68a0113b75a
intermediate version -- why not...
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|
811 version) you are using it will be difficult for me to figure out what |
|
c68a0113b75a
intermediate version -- why not...
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parents:
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|
812 is the matter. If you get a specific error message, please email it |
|
c68a0113b75a
intermediate version -- why not...
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parents:
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|
813 to me too. |
| 1529 | 814 |
|
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|
815 3.13. Q. How to configure dynamic loading on Lixux. |
| 2301 | 816 |
| 2855 | 817 A. There are two answers, depending on whether you are using the new |
| 818 ELF object format or not. | |
| 2301 | 819 |
| 2855 | 820 For ELF, this seems to be the procedure (thanks to Martin von Loewis): |
| 821 | |
| 822 Compile Python to an ELF binary. | |
| 823 | |
| 824 In addition, you have to use the following flags: | |
| 2301 | 825 |
| 2855 | 826 - when linking python: -rdynamic -ldl |
| 827 - when compiling an object that goes into a shared module: -fPIC | |
| 828 - when linking a shared module: -shared -ldl | |
| 829 | |
| 830 Furthermore, it appears that some Python releases did not understand | |
| 831 that Linux has dynamic linking. Python 1.2 did it right, but you | |
| 832 should check wether the generated config.h indicates the use of -ldl | |
| 833 (i.e. dlopen, dlsym). Finally, you can load a shared module by saying | |
| 834 'use foo'. Make sure the module is in your PYTHONPATH. | |
| 835 | |
| 836 For pre-ELF systems (thanks to Andrew Kuchling): | |
| 837 | |
| 838 Pre-ELF Linux requires that you use the GNU DLD library. The stages | |
| 839 of using dynamic libraries on Linux are: | |
|
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|
840 |
| 2855 | 841 1) Get dld 3.2.5 from a Linux site. Be careful here; the most |
| 842 recent GNU version is 3.2.3, and doesn't support Linux; be sure to | |
| 843 get it from a Linux mirror, not a GNU mirror (3.2.4 should also | |
| 844 work). Compile it and install the library libdld.a somewhere; I | |
| 845 used /usr/local/lib. | |
| 2301 | 846 |
| 2855 | 847 Suitable URLs for the dld distribution are currently: |
| 848 <URL:ftp://sunsite.unc.edu/pub/Linux/libs/dld-3.2.5.src.tar.gz> and | |
| 849 <URL:ftp://tsx-11.mit.edu/pub/linux/sources/libs/dld-3.2.5.src.tar.gz>. | |
| 850 There's also a binary distribution of it: | |
| 851 <URL:ftp://sunsite.unc.edu/pub/Linux/libs/dld-3.2.5.bin.tar.gz>. | |
| 852 | |
| 853 2) Get Jack Jansen's DL library; its location is given in the | |
| 854 _Extending Python_ manual as <URL:ftp://ftp.cwi.nl/pub/dynload/>. | |
| 855 Compile it and install libdl.a wherever you put libdld.a. | |
| 2301 | 856 |
| 2855 | 857 3) Run Python's configure script, giving it the --with-dl-dld option, |
| 858 which requires a parameter giving the directory where you put the | |
| 859 libraries. | |
| 860 | |
| 861 4) Recompile Python. | |
| 862 | |
| 863 3.14. Q. Under Solaris 2.x, using GCC, how do I use shared libraries? | |
| 2301 | 864 |
| 2855 | 865 A. Use the linker in /usr/ucb/ld, not the GNU linker. The latter |
| 866 cannot create shared libraries. | |
| 2301 | 867 |
| 2855 | 868 3.15. Q. Errors when linking with a shared library containing C++ code. |
| 869 | |
| 870 A. Link the main Python binary with C++. Change the definition of | |
| 871 LINKCC in Modules/Makefile to be your C++ compiler. You may have to | |
| 872 edit config.c slightly to make it compilable with C++. | |
| 2301 | 873 |
|
3126
e90643f33c64
+aaron watters, +PSA, +GC, -lance, -beta
Guido van Rossum <guido@python.org>
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diff
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|
874 3.16. Q. Tk menus or radiobuttons don't work properly in Python 1.2. |
|
3023
87847228b158
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|
875 |
|
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|
876 A. There's a bug in Tkinter.py; remove ClassType and InstanceType from |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
877 the definition of CallableTypes near the top of Lib/tkinter/Tkinter.py. |
|
87847228b158
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|
878 |
|
3233
fd573ac75947
Renamed module tkinter to _tkinter
Jack Jansen <jack.jansen@cwi.nl>
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3207
diff
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|
879 3.17. Q. I built with _tkintermodule.c enabled but get "Tkinter not found". |
|
3023
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|
880 |
|
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|
881 A. Tkinter.py (note: upper case T) lives in a subdirectory of Lib, |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
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|
882 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>
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|
883 probably didn't enable the line in the Modules/Setup file defining |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
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|
884 TKPATH; if you use the environment variable PYTHONPATH, you'll have to |
|
87847228b158
several new questions, 1.3 beta mentioned
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3018
diff
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|
885 add the proper tkinter subdirectory. |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
886 |
|
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several new questions, 1.3 beta mentioned
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parents:
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|
887 3.18. Q. I built with Tk 4.0 but Tkinter complains about the Tk version. |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
888 |
|
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several new questions, 1.3 beta mentioned
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|
889 A. Several things could cause this. You most likely have a Tk 3.6 |
|
87847228b158
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|
890 installation that wasn't completely eradicated by the Tk 4.0 |
|
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|
891 installation (which tends to add "4.0" to its installed files). You |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
892 may have the Tk 3.6 support library installed in the place where the |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
893 Tk 4.0 support files should be (default /usr/local/lib/tk/); you may |
|
87847228b158
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|
894 have compiled Python with the old tk.h header file (yes, this actually |
|
87847228b158
several new questions, 1.3 beta mentioned
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parents:
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|
895 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>
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|
896 4.0 is also around. Similar for Tcl 7.4 vs. Tcl 7.3. |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
897 |
|
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|
898 3.19. Q. Tk doesn't work right on DEC Alpha. |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
899 |
|
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|
900 A. You probably compiled either Tcl, Tk or Python with gcc. Don't. |
|
87847228b158
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|
901 For this platform, which has 64-bit integers, gcc is known to generate |
|
87847228b158
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|
902 broken code. The standard cc (which comes bundled with the OS!) |
|
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|
903 works. If you still prefer gcc, at least try recompiling with cc |
|
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|
904 before reporting problems to the newsgroup or the author; if this |
|
87847228b158
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|
905 fixes the problem, report the bug to the gcc developers instead. (As |
|
87847228b158
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|
906 far as we know, there are no problem with gcc on other platforms -- |
|
87847228b158
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|
907 the instabilities seem to be restricted to the DEC Alpha.) See also |
|
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|
908 question 3.6. |
|
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|
909 |
| 1529 | 910 |
| 911 4. Programming in Python | |
| 912 ======================== | |
| 913 | |
|
1541
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914 4.1. Q. Is there a source code level debugger with breakpoints, step, |
|
630e03109c63
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915 etc.? |
|
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916 |
|
630e03109c63
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917 A. Yes. Check out module pdb; pdb.help() prints the documentation (or |
|
630e03109c63
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918 you can read it as Lib/pdb.doc). If you use the STDWIN option, |
|
630e03109c63
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919 there's also a windowing interface, wdb. You can write your own |
|
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Released version 1.4; out after 1.0.0 is released...
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920 debugger by using the code for pdb or wdb as an example. |
|
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921 |
|
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922 4.2. Q. Can I create an object class with some methods implemented in |
| 1529 | 923 C and others in Python (e.g. through inheritance)? (Also phrased as: |
| 924 Can I use a built-in type as base class?) | |
| 925 | |
| 926 A. No, but you can easily create a Python class which serves as a | |
| 927 wrapper around a built-in object, e.g. (for dictionaries): | |
| 928 | |
| 2048 | 929 # A user-defined class behaving almost identical |
| 930 # to a built-in dictionary. | |
| 931 class UserDict: | |
| 932 def __init__(self): self.data = {} | |
| 933 def __repr__(self): return repr(self.data) | |
| 934 def __cmp__(self, dict): | |
| 935 if type(dict) == type(self.data): | |
| 936 return cmp(self.data, dict) | |
| 937 else: | |
| 938 return cmp(self.data, dict.data) | |
| 939 def __len__(self): return len(self.data) | |
| 940 def __getitem__(self, key): return self.data[key] | |
| 941 def __setitem__(self, key, item): self.data[key] = item | |
| 942 def __delitem__(self, key): del self.data[key] | |
| 943 def keys(self): return self.data.keys() | |
| 944 def items(self): return self.data.items() | |
| 945 def values(self): return self.data.values() | |
| 946 def has_key(self, key): return self.data.has_key(key) | |
| 1529 | 947 |
|
1541
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948 4.3. Q. Is there a curses/termcap package for Python? |
| 1529 | 949 |
| 2048 | 950 A. Yes -- Lance Ellinghaus has written a module that interfaces to |
|
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951 System V's "ncurses". If you know a little curses and some Python, |
| 2048 | 952 it's straightforward to use. It is part of the standard Python |
| 953 distribution, but not configured by default -- you must enable it by | |
| 954 editing Modules/Setup. It requires a System V curses implementation. | |
|
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955 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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956 You could also consider using the "alfa" (== character cell) version |
| 2048 | 957 of STDWIN. (Standard Window System Interface, a portable windowing |
| 958 system interface by myself <URL:ftp://ftp.cwi.nl/pub/stdwin/>.) This | |
|
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959 will also prepare your program for porting to windowing environments |
|
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960 such as X11 or the Macintosh. |
| 1529 | 961 |
|
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|
962 4.4. Q. Is there an equivalent to C's onexit() in Python? |
| 1529 | 963 |
| 964 A. Yes, if you import sys and assign a function to sys.exitfunc, it | |
| 965 will be called when your program exits, is killed by an unhandled | |
| 966 exception, or (on UNIX) receives a SIGHUP or SIGTERM signal. | |
| 967 | |
|
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968 4.5. Q. When I define a function nested inside another function, the |
| 1529 | 969 nested function seemingly can't access the local variables of the |
| 970 outer function. What is going on? How do I pass local data to a | |
| 971 nested function? | |
| 972 | |
| 973 A. Python does not have arbitrarily nested scopes. When you need to | |
| 974 create a function that needs to access some data which you have | |
| 975 available locally, create a new class to hold the data and return a | |
| 976 method of an instance of that class, e.g.: | |
| 977 | |
| 2048 | 978 class MultiplierClass: |
| 979 def __init__(self, factor): | |
| 980 self.factor = factor | |
| 981 def multiplier(self, argument): | |
| 982 return argument * self.factor | |
| 983 | |
| 984 def generate_multiplier(factor): | |
| 985 return MultiplierClass(factor).multiplier | |
| 1529 | 986 |
| 2048 | 987 twice = generate_multiplier(2) |
| 988 print twice(10) | |
| 989 # Output: 20 | |
| 990 | |
| 991 An alternative solution uses default arguments, e.g.: | |
| 1529 | 992 |
| 2048 | 993 def generate_multiplier(factor): |
| 994 def multiplier(arg, fact = factor): | |
| 995 return arg*fact | |
| 996 return multiplier | |
| 997 | |
| 998 twice = generate_multiplier(2) | |
| 999 print twice(10) | |
| 1000 # Output: 20 | |
| 1529 | 1001 |
|
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|
1002 4.6. Q. How do I iterate over a sequence in reverse order? |
| 1529 | 1003 |
| 1004 A. If it is a list, the fastest solution is | |
| 1005 | |
| 2048 | 1006 list.reverse() |
| 1007 try: | |
| 1008 for x in list: | |
| 1009 "do something with x" | |
| 1010 finally: | |
| 1011 list.reverse() | |
| 1529 | 1012 |
| 1013 This has the disadvantage that while you are in the loop, the list | |
| 1014 is temporarily reversed. If you don't like this, you can make a copy. | |
| 1015 This appears expensive but is actually faster than other solutions: | |
| 1016 | |
| 2048 | 1017 rev = list[:] |
| 1018 rev.reverse() | |
| 1019 for x in rev: | |
| 1020 <do something with x> | |
| 1529 | 1021 |
| 1022 If it isn't a list, a more general but slower solution is: | |
| 1023 | |
| 2048 | 1024 i = len(list) |
| 1025 while i > 0: | |
| 1026 i = i-1 | |
| 1027 x = list[i] | |
| 1028 <do something with x> | |
| 1529 | 1029 |
| 1030 A more elegant solution, is to define a class which acts as a sequence | |
| 1031 and yields the elements in reverse order (solution due to Steve | |
| 1032 Majewski): | |
| 1033 | |
| 2048 | 1034 class Rev: |
| 1035 def __init__(self, seq): | |
| 1036 self.forw = seq | |
| 1037 def __len__(self): | |
| 1038 return len(self.forw) | |
| 1039 def __getitem__(self, i): | |
| 1040 return self.forw[-(i + 1)] | |
| 1529 | 1041 |
| 1042 You can now simply write: | |
| 1043 | |
| 2048 | 1044 for x in Rev(list): |
| 1045 <do something with x> | |
| 1529 | 1046 |
| 1942 | 1047 Unfortunately, this solution is slowest of all, due to the method |
| 1529 | 1048 call overhead... |
| 1049 | |
|
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|
1050 4.7. Q. My program is too slow. How do I speed it up? |
| 1529 | 1051 |
| 1052 A. That's a tough one, in general. There are many tricks to speed up | |
| 1053 Python code; I would consider rewriting parts in C only as a last | |
| 1054 resort. One thing to notice is that function and (especially) method | |
| 1055 calls are rather expensive; if you have designed a purely OO interface | |
| 1056 with lots of tiny functions that don't do much more than get or set an | |
| 1057 instance variable or call another method, you may consider using a | |
| 1058 more direct way, e.g. directly accessing instance variables. Also see | |
| 1059 the standard module "profile" (described in the file | |
| 1060 "python/lib/profile.doc") which makes it possible to find out where | |
| 1061 your program is spending most of its time (if you have some patience | |
| 1062 -- the profiling itself can slow your program down by an order of | |
| 1063 magnitude). | |
| 1064 | |
|
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|
1065 4.8. Q. When I have imported a module, then edit it, and import it |
| 1529 | 1066 again (into the same Python process), the changes don't seem to take |
| 1067 place. What is going on? | |
| 1068 | |
| 2048 | 1069 A. For reasons of efficiency as well as consistency, Python only reads |
|
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1070 the module file on the first time a module is imported. (Otherwise a |
| 2048 | 1071 program consisting of many modules, each of which imports the same |
|
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1072 basic module, would read the basic module over and over again.) To |
|
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1073 force rereading of a changed module, do this: |
| 1529 | 1074 |
| 2048 | 1075 import modname |
| 1076 reload(modname) | |
| 1529 | 1077 |
| 1078 Warning: this technique is not 100% fool-proof. In particular, | |
| 1079 modules containing statements like | |
| 1080 | |
| 2048 | 1081 from modname import some_objects |
| 1529 | 1082 |
|
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1083 will continue to work with the old version of the imported objects. |
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1084 |
|
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1085 4.9. Q. How do I find the current module name? |
| 1529 | 1086 |
| 1942 | 1087 A. A module can find out its own module name by looking at the |
|
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|
1088 (predefined) global variable __name__. If this has the value |
|
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1089 '__main__' you are running as a script. |
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1090 |
| 2048 | 1091 4.10. Q. I have a module in which I want to execute some extra code |
| 1092 when it is run as a script. How do I find out whether I am running as | |
| 1093 a script? | |
|
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1094 |
|
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1095 A. See the previous question. E.g. if you put the following on the |
|
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1096 last line of your module, main() is called only when your module is |
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1097 running as a script: |
|
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1098 |
| 2048 | 1099 if __name__ == '__main__': main() |
|
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1100 |
| 2048 | 1101 4.11. Q. I try to run a program from the Demo directory but it fails |
| 1102 with ImportError: No module named ...; what gives? | |
| 1663 | 1103 |
| 1942 | 1104 A. This is probably an optional module (written in C!) which hasn't |
| 1105 been configured on your system. This especially happens with modules | |
| 2048 | 1106 like "Tkinter", "stdwin", "gl", "Xt" or "Xm". For Tkinter, STDWIN and |
| 1107 many other modules, see Modules/Setup.in for info on how to add these | |
| 1108 modules to your Python, if it is possible at all. Sometimes you will | |
| 1109 have to ftp and build another package first (e.g. STDWIN). Sometimes | |
| 1110 the module only works on specific platforms (e.g. gl only works on SGI | |
| 1111 machines). | |
| 1112 | |
| 1113 NOTE: if the complaint is about "Tkinter" (upper case T) and you have | |
|
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|
1114 already configured module "_tkinter" (lower case t and underscore), |
|
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1115 the solution is *not* to rename tkinter to Tkinter or vice versa. |
|
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1116 There is probably something wrong with your module search path. Check |
|
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1117 out the value of sys.path. |
| 1663 | 1118 |
| 1942 | 1119 For X-related modules (Xt and Xm) you will have to do more work: they |
| 1120 are currently not part of the standard Python distribution. You will | |
| 2048 | 1121 have to ftp the Extensions tar file, e.g. |
|
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1122 <URL:ftp://ftp.python.org/pub/python/src/extensions.tar.gz> and follow |
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1123 the instructions there. |
| 1942 | 1124 |
| 1125 See also the next question. | |
| 1126 | |
| 1127 4.12. Q. I have successfully built Python with STDWIN but it can't | |
| 1128 find some modules (e.g. stdwinevents). | |
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1129 |
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1130 A. There's a subdirectory of the library directory named 'stdwin' |
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1131 which should be in the default module search path. There's a line in |
|
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1132 Modules/Setup(.in) that you have to enable for this purpose -- |
| 1942 | 1133 unfortunately in the latest release it's not near the other |
|
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1134 STDWIN-related lines so it's easy to miss it. |
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1135 |
|
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1136 4.13. Q. What GUI toolkits exist for Python? |
| 1663 | 1137 |
| 1138 A. Depending on what platform(s) you are aiming at, there are several. | |
| 1139 | |
|
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1140 - There's a neat object-oriented interface to the Tcl/Tk widget set, |
| 2048 | 1141 called Tkinter. As of python 1.1, it is part of the standard Python |
| 1142 distribution -- all you need to do is enable it in Modules/Setup | |
| 1143 (provided you have already installed Tk and Tcl). This is probably | |
| 1144 the easiest to install and use, and the most complete widget set. It | |
| 1145 is also very likely that in the future the standard Python GUI API | |
| 1146 will be based on or at least look very much like the Tkinter | |
| 1147 interface. For more info about Tk, including pointers to the source, | |
| 3018 | 1148 see the Tcl/Tk home page <URL:http://www.sunlabs.com/research/tcl/>. |
|
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1149 |
| 1663 | 1150 - The standard Python distribution comes with an interface to STDWIN, |
| 2048 | 1151 a platform-independent low-level windowing interface. You have to ftp |
| 1152 the source for STDWIN separately, | |
| 1153 e.g. <URL:ftp://ftp.cwi.nl/pub/stdwin/> or gatekeeper.dec.com in | |
| 1154 pub/misc/stdwin <URL:ftp://gatekeeper.dec.com/pub/misc/stdwin/>. | |
| 1155 STDWIN runs under X11 or the Mac; a Windows port has been attempted | |
| 1156 but I can't seem to get it working. Note that STDWIN is really not | |
| 1157 powerful enough to implement a modern GUI (no widgets, etc.) and that | |
| 1158 I don't have the time to maintain or extend it, so you may be better | |
| 1159 off using Tkinter or the Motif interface, unless you require | |
| 1160 portability to the Mac (which is also offered by SUIT, by the way -- | |
| 1161 see below). | |
| 1663 | 1162 |
|
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|
1163 - For SGI IRIX only, there's an interface to the complete GL (Graphics |
| 1663 | 1164 Library -- low level but very good 3D capabilities) as well as to |
| 1165 FORMS (a buttons-and-sliders-etc package built on top of GL by Mark | |
| 2048 | 1166 Overmars -- ftp'able from <URL:ftp://ftp.cs.ruu.nl/pub/SGI/FORMS/>). |
| 1663 | 1167 |
| 1168 - There's an interface to X11, including the Athena and Motif widget | |
| 1169 sets (and a few individual widgets, like Mosaic's HTML widget and | |
| 1170 SGI's GL widget) in the Extensions set, which is separately ftp'able | |
|
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1171 <URL:ftp://ftp.python.org/pub/python/src/extensions.tar.gz>. |
| 1663 | 1172 |
| 1173 - There's an interface to SUIT, the U of Virginia's Simple User | |
| 2048 | 1174 Interface Toolkit; it can be ftp'ed from |
| 1175 <URL:ftp://uvacs.cs.virginia.edu/pub/suit/python/SUIT_python.tar.Z>. | |
| 1176 A PC binary of Python 1.0.2 compiled with DJGPP and with SUIT support | |
| 1177 built-in has been made available by Antonio Costa | |
| 1178 <URL:ftp://asterix.inescn.pt/pub/PC/python/pyt102su.exe> (a | |
| 1179 self-extracting archive). Note that the UVa people themselves have | |
| 1180 expressed doubts about SUIT, and are planning to build a Python GUI | |
| 1181 API based upon Tk (though not necessarily on Tkinter); see | |
| 1182 <URL:http://server.cs.virginia.edu/~tnb2d/IT/IT.html>. | |
| 1663 | 1183 |
| 1184 - There's an interface to WAFE, a Tcl interface to the X11 Motif and | |
| 2048 | 1185 Athena widget sets. Last I heard about it it was included in the WAFE |
| 1186 1.0 prerelease | |
| 1187 <URL:ftp://ftp.wu-wien.ac.at/pub/src/X11/wafe/wafe-1.0.tar.gz-prerelease>. | |
| 1663 | 1188 |
| 3018 | 1189 - The NT port by Mark Hammond (see question 7.4) includes an interface |
| 1190 to the Microsoft Foundation Classes and a Python programming | |
| 1191 environment using it that's written mostly in Python. See | |
| 1192 <URL:ftp://ftp.python.org/pub/python/nt/>. | |
| 1193 | |
|
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1194 - There's an interface to wxWindows. wxWindows is a portable GUI |
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1195 class library written in C++. It supports XView, Motif, MS-Windows as |
|
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1196 targets. There is some support for Macs and CURSES as well. wxWindows |
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1197 preserves the look and feel of the underlying graphics toolkit. See |
|
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1198 the wxPython WWW page at |
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1199 <URL:http://www.aiai.ed.ac.uk/~jacs/wx/wxpython/wxpython.html>. |
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1200 |
| 2855 | 1201 - There's an object-oriented GUI based on the Microsoft Foundation |
| 1202 Classes model called WPY. Programs written in WPY run unchanged and | |
| 1203 with native look and feel on NT, Windows 3.1 (using win32s) and on | |
| 1204 Unix (using Tk). Source and binaries for NT and Linux are available | |
| 1205 in <URL:ftp://ftp.python.org/pub/python/wpy>. | |
| 1206 | |
|
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1207 - Python has been mentioned on the "Futurism" subpage of the Fresco |
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1208 home page <URL:http://www.faslab.com/fresco/HomePage.html>. "Pesto" |
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1209 is a Python interface to the CORBA dynamic invocation interface, and |
|
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1210 thus Fresco. A Pesto prototype is running and is currently being |
|
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1211 packaged up for inclusion in the Fresco snapshot. See also the Pesto |
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1212 web pages: <URL:http://www.faslab.com/fresco/pesto/Index.html>. |
|
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1213 |
| 1942 | 1214 4.14. Q. Are there any interfaces to database packages in Python? |
| 1663 | 1215 |
| 1216 A. There's an interface to SYBASE by John Redford | |
| 1217 <jredford@lehman.com>. | |
| 1218 | |
|
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1219 There's an interface to metalbase by Lance Ellinghaus |
| 2048 | 1220 <lance@markv.com>; it is part of the separate Extensions distribution |
|
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1221 <URL:ftp://ftp.python.org/pub/python/src/extensions.tar.gz>. |
| 1663 | 1222 |
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1223 Anthony Baxter <anthony.baxter@aaii.oz.au> has written an interface to |
|
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1224 mSQL (mini-SQL). |
|
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1225 <URL:ftp://ftp.python.org/pub/python/contrib/PymSQL.tar.gz>. |
|
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|
1226 |
|
2716
19b1195a3af8
next version; python.org changes
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|
1227 Tom Culliton <culliton@clark.net> has written an Oracle module. |
|
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next version; python.org changes
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1228 See <URL:ftp://ftp.clark.net/pub/culliton/oramod.tgz>. |
|
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1229 |
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1230 4.15. Q. Is it possible to write obfuscated one-liners in Python? |
|
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Added obfuxcated lambda's by Ulf Bertelt
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1231 |
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Added obfuxcated lambda's by Ulf Bertelt
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|
1232 A. Yes. See the following three examples, due to Ulf Bartelt: |
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Added obfuxcated lambda's by Ulf Bertelt
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|
1233 |
| 2048 | 1234 # Primes < 1000 |
| 1235 print filter(None,map(lambda y:y*reduce(lambda x,y:x*y!=0, | |
| 1236 map(lambda x,y=y:y%x,range(2,int(pow(y,0.5)+1))),1),range(2,1000))) | |
|
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Added obfuxcated lambda's by Ulf Bertelt
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|
1237 |
| 2048 | 1238 # First 10 Fibonacci numbers |
| 1239 print map(lambda x,f=lambda x,f:(x<=1) or (f(x-1,f)+f(x-2,f)): f(x,f), | |
| 1240 range(10)) | |
|
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Added obfuxcated lambda's by Ulf Bertelt
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|
1241 |
| 2048 | 1242 # Mandelbrot set |
| 1243 print (lambda Ru,Ro,Iu,Io,IM,Sx,Sy:reduce(lambda x,y:x+y,map(lambda y, | |
| 1244 Iu=Iu,Io=Io,Ru=Ru,Ro=Ro,Sy=Sy,L=lambda yc,Iu=Iu,Io=Io,Ru=Ru,Ro=Ro,i=IM, | |
| 1245 Sx=Sx,Sy=Sy:reduce(lambda x,y:x+y,map(lambda x,xc=Ru,yc=yc,Ru=Ru,Ro=Ro, | |
| 1246 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 | |
| 1247 >=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( | |
| 1248 64+F(Ru+x*(Ro-Ru)/Sx,yc,0,0,i)),range(Sx))):L(Iu+y*(Io-Iu)/Sy),range(Sy | |
| 1249 ))))(-2.1, 0.7, -1.2, 1.2, 30, 80, 24) | |
| 1250 # \___ ___/ \___ ___/ | | |__ lines on screen | |
| 1251 # V V | |______ columns on screen | |
| 1252 # | | |__________ maximum of "iterations" | |
| 1253 # | |_________________ range on y axis | |
| 1254 # |____________________________ range on x axis | |
|
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1255 |
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Added obfuxcated lambda's by Ulf Bertelt
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|
1256 Don't try this at home, kids! |
|
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Added obfuxcated lambda's by Ulf Bertelt
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1257 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1258 4.16. Q. Is there an equivalent of C's "?:" ternary operator? |
|
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1259 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1260 A. Not directly. In many cases you can mimic a?b:c with "a and b or |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1261 c", but there's a flaw: if b is zero (or empty, or None -- anything |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1262 that tests false) then c will be selected instead. In many cases you |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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1263 can prove by looking at the code that this can't happen (e.g. because |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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1264 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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1265 this can be a problem. |
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New version: 1.14 (previous oine was misnumbered 1.12).
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1266 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1267 Steve Majewski (or was it Tim Peters?) suggested the following |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1268 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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1269 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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1270 the whole thing gets the b or c that you really wanted. Ugly, but it |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1271 gets you there in the rare cases where it is really inconvenient to |
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1272 rewrite your code using 'if'. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1273 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1274 4.17. Q. My class defines __del__ but it is not called when I delete the |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1275 object. |
|
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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 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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|
1278 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1279 - The del statement does not necessarily call __del__ -- it simply |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1280 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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|
1281 __del__ is called. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1282 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1283 - If your data structures contain circular links (e.g. a tree where |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1284 each child has a parent pointer and each parent has a list of |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1285 children) the reference counts will never go back to zero. You'll |
| 1942 | 1286 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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|
1287 pointers. Please don't ever call __del__ directly -- __del__ should |
| 1942 | 1288 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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|
1289 than once for the same object. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1290 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1291 - If the object has ever been a local variable (or argument, which is |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1292 really the same thing) to a function that caught an expression in an |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1293 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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|
1294 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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|
1295 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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1296 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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|
1297 exception in an interactive interpreter, delete sys.last_traceback |
|
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|
1298 instead. |
|
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|
1299 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1300 - 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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|
1301 but if your Python has been configured to support threads, it is not |
|
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|
1302 called (because other threads may still be active). You can define |
| 1942 | 1303 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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|
1304 |
| 2048 | 1305 - Finally, there are some obscure bugs if your __del__ method does |
| 1306 complicated things such as updating dictionaries or lists or | |
| 1307 references globals. I hope to have fixed these in release 1.2. | |
| 1308 | |
| 1309 4.18. Q. How do I change the shell environment for programs called | |
| 1310 using os.popen() or os.system()? Changing os.environ doesn't work. | |
|
1903
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|
1311 |
|
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|
1312 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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|
1313 interpreter because there seemed to be no well-established portable |
| 2048 | 1314 way to do it (in particular, some systems, have putenv(), others have |
| 1315 setenv(), and some have none at all). | |
|
1903
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1316 |
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|
1317 However if all you want is to pass environment variables to the |
|
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|
1318 commands run by os.system() or os.popen(), there's a simple solution: |
|
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|
1319 prefix the command string with a couple of variable assignments and |
|
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|
1320 export statements. The following would be universal for popen: |
|
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|
1321 |
| 2048 | 1322 import os |
| 1323 from commands import mkarg # nifty routine to add shell quoting | |
| 1324 def epopen(cmd, mode, env = {}): | |
| 1325 # env is a dictionary of environment variables | |
| 1326 prefix = '' | |
|
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1327 for key, value in env.items(): |
|
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|
1328 prefix = prefix + '%s=%s\n' % (key, mkarg(value)[1:]) |
| 2048 | 1329 prefix = prefix + 'export %s\n' % key |
| 1330 return os.popen(prefix + cmd, mode) | |
|
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1331 |
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1332 4.19. Q. What is a class? |
|
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1333 |
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1334 A. A class is the particular object type that is created by executing |
|
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1335 a class statement. Class objects are used as templates, to create |
|
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1336 class instance objects, which embody both the data structure and |
|
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1337 program routines specific to a datatype. |
|
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1338 |
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1339 4.20. Q. What is a method? |
|
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1340 |
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|
1341 A. A method is a function that you normally call as |
|
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|
1342 x.name(arguments...) for some object x. The term is used for methods |
|
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|
1343 of classes and class instances as well as for methods of built-in |
|
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1344 objects. (The latter have a completely different implementation and |
|
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|
1345 only share the way their calls look in Python code.) Methods of |
|
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1346 classes (and class instances) are defined as functions inside the |
|
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1347 class definition. |
|
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1348 |
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1349 4.21. Q. What is self? |
|
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1350 |
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|
1351 A. Self is merely a conventional name for the first argument of a |
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|
1352 method -- i.e. a function defined inside a class definition. A method |
|
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1353 defined as meth(self, a, b, c) should be called as x.meth(a, b, c) for |
|
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1354 some instance x of the class in which the definition occurs; |
|
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|
1355 the called method will think it is called as meth(x, a, b, c). |
|
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1356 |
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|
1357 4.22. Q. What is a unbound method? |
|
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1358 |
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|
1359 A. An unbound method is a method defined in a class that is not yet |
|
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|
1360 bound to an instance. You get an unbound method if you ask for a |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1361 class attribute that happens to be a function. You get a bound method |
|
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|
1362 if you ask for an instance attribute. A bound method knows which |
| 1942 | 1363 instance it belongs to and calling it supplies the instance automatically; |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1364 an unbound method only knows which class it wants for its first |
|
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|
1365 argument (a derived class is also OK). Calling an unbound method |
|
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1366 doesn't "magically" derive the first argument from the context -- you |
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New version: 1.14 (previous oine was misnumbered 1.12).
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1367 have to provide it explicitly. |
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1368 |
| 2048 | 1369 4.23. Q. How do I call a method defined in a base class from a derived |
| 1370 class that overrides it? | |
|
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|
1371 |
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|
1372 A. If your class definition starts with "class Derived(Base): ..." |
|
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1373 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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1374 classes) as Base.meth(self, arguments...). Here, Base.meth is an |
|
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|
1375 unbound method (see previous question). |
|
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1376 |
| 2048 | 1377 4.24. Q. How do I call a method from a base class without using the |
| 1378 name of the base class? | |
|
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1379 |
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|
1380 A. DON'T DO THIS. REALLY. I MEAN IT. It appears that you could call |
|
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1381 self.__class__.__bases__[0].meth(self, arguments...) but this fails when |
| 1942 | 1382 a doubly-derived method is derived from your class: for its instances, |
|
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1383 self.__class__.__bases__[0] is your class, not its base class -- so |
|
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1384 (assuming you are doing this from within Derived.meth) you would start |
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1385 a recursive call. |
|
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1386 |
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|
1387 4.25. Q. How can I organize my code to make it easier to change the base |
|
e450bd43631a
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|
1388 class? |
|
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1389 |
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|
1390 A. You could define an alias for the base class, assign the real base |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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1391 class to it before your class definition, and use the alias throughout |
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1392 your class. Then all you have to change is the value assigned to the |
|
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|
1393 alias. Incidentally, this trick is also handy if you want to decide |
|
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|
1394 dynamically (e.g. depending on availability of resources) which base |
|
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|
1395 class to use. Example: |
|
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|
1396 |
|
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|
1397 BaseAlias = <real base class> |
|
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|
1398 class Derived(BaseAlias): |
| 2048 | 1399 def meth(self): |
| 1400 BaseAlias.meth(self) | |
| 1401 ... | |
|
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|
1402 |
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|
1403 4.26. Q. How can I find the methods or attributes of an object? |
|
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|
1404 |
|
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|
1405 A. This depends on the object type. |
|
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|
1406 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1407 For an instance x of a user-defined class, instance attributes are |
|
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|
1408 found in the dictionary x.__dict__, and methods and attributes defined |
|
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1409 by its class are found in x.__class__.__bases__[i].__dict__ (for i in |
|
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|
1410 range(len(x.__class__.__bases__))). You'll have to walk the tree of |
|
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|
1411 base classes to find *all* class methods and attributes. |
|
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|
1412 |
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|
1413 Many, but not all built-in types define a list of their method names |
|
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|
1414 in x.__methods__, and if they have data attributes, their names may be |
|
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|
1415 found in x.__members__. However this is only a convention. |
|
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|
1416 |
|
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|
1417 For more information, read the source of the standard (but |
|
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|
1418 undocumented) module newdir. |
|
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|
1419 |
|
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|
1420 4.27. Q. I can't seem to use os.read() on a pipe created with os.popen(). |
|
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|
1421 |
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|
1422 A. os.read() is a low-level function which takes a file descriptor (a |
|
e450bd43631a
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|
1423 small integer). os.popen() creates a high-level file object -- the |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1424 same type used for sys.std{in,out,err} and returned by the builtin |
|
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|
1425 open() function. Thus, to read n bytes from a pipe p created with |
|
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|
1426 os.popen(), you need to use p.read(n). |
| 1529 | 1427 |
| 1942 | 1428 4.28. Q. How can I create a stand-alone binary from a Python script? |
| 1429 | |
| 1430 The demo script "Demo/scripts/freeze.py" does what you want. (It's | |
| 1431 actually not a demo but a support tool -- there is some extra code in | |
| 1432 the interpreter to accommodate it.) It requires that you have the | |
| 1433 Python build tree handy, complete with all the lib*.a files. | |
| 1434 | |
| 1435 This works by scanning your source recursively for import statements | |
| 1436 (both forms) and looking for the modules on the standard Python path | |
| 1437 as well as in the source directory (for built-in modules). It then | |
| 1438 "compiles" the modules written in Python to C code (array initializers | |
| 1439 that can be turned into code objects using the marshal module) and | |
| 1440 creates a custom-made config file that only contains those built-in | |
| 1441 modules which are actually used in the program. It then compiles the | |
| 1442 generated C code and links it with the rest of the Python interpreter | |
| 1443 to form a self-contained binary which acts exactly like your script. | |
| 1444 | |
|
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|
1445 Hint: the freeze program only works if your script's filename ends in |
|
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|
1446 ".py". |
| 1942 | 1447 |
|
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|
1448 4.29. Q. What WWW tools are there for Python? |
| 1942 | 1449 |
|
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|
1450 A. There's a whole lot in the 1.2 release; see the section on |
|
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|
1451 "Internet and WWW" in the Library Reference Manual. Highlights: a CGI |
|
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|
1452 parser, a url retriever, an html parser. |
| 1942 | 1453 |
| 1454 Steve Miale <smiale@cs.indiana.edu> has written a modular WWW browser | |
| 1455 called Dancer. An alpha version can be FTP'ed from | |
| 2048 | 1456 <URL:ftp://ftp.cs.indiana.edu/pub/smiale/dancer.tar.gz>. (There are a |
| 1457 few articles about Dancer in the (hyper)mail archive | |
| 1458 <URL:http://www.cwi.nl/~guido/hypermail/python-1994q3/index.html>.) | |
| 1942 | 1459 |
|
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1460 4.30. Q. How do I run a subprocess with pipes connected to both input |
|
2208
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|
1461 and output? |
|
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|
1462 |
|
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|
1463 A. This is really a UNIX question. Also, in general, it is unwise to |
|
c68a0113b75a
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|
1464 do so, because you can easily cause a deadlock where the parent |
|
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1465 process is blocked waiting for output from the child, while the child |
|
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|
1466 is blocked waiting for input from the child. This can be caused |
|
c68a0113b75a
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|
1467 because the parent expects the child to output more text than it does, |
|
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|
1468 or it can be caused by data being stuck in stdio buffers due to lack |
|
c68a0113b75a
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|
1469 of flushing. The Python parent can of course explicitly flush the data |
|
c68a0113b75a
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|
1470 it sends to the child before it reads any output, but if the child is |
|
c68a0113b75a
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|
1471 a naive C program it can easily have been written to never explicitly |
|
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|
1472 flush its output, even if it is interactive, since flushing is |
|
c68a0113b75a
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|
1473 normally automatic. |
|
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|
1474 |
|
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|
1475 In many cases, all you really need is to run some data through a |
|
c68a0113b75a
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|
1476 command and get the result back. Unless the data is infinite in size, |
|
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|
1477 the easiest (and often the most efficient!) way to do this is to write |
|
c68a0113b75a
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|
1478 it to a temporary file and run the command with that temporary file as |
|
c68a0113b75a
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|
1479 input. The standard module tempfile exports a function mktemp() which |
|
c68a0113b75a
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1480 generates unique temporary file names. |
|
c68a0113b75a
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|
1481 |
|
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|
1482 If after reading all of the above you still want to connect two pipes |
|
c68a0113b75a
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|
1483 to a subprocess's standard input and output, here's a simple solution, |
|
c68a0113b75a
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|
1484 due to Jack Jansen: |
|
c68a0113b75a
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|
1485 |
|
3207
0ed5cd8df51f
all sorts of minor nits
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|
1486 import os |
|
0ed5cd8df51f
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|
1487 import sys |
|
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|
1488 import string |
|
2208
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|
1489 |
|
3207
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1490 MAXFD = 100 # Max number of file descriptors in this system |
|
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1491 |
|
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1492 def popen2(cmd): |
|
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1493 cmd = string.split(cmd) |
|
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1494 p2cread, p2cwrite = os.pipe() |
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1495 c2pread, c2pwrite = os.pipe() |
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1496 pid = os.fork() |
|
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1497 if pid == 0: |
|
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1498 # Child |
|
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1499 os.close(0) |
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1500 os.close(1) |
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1501 if os.dup(p2cread) <> 0: |
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1502 sys.stderr.write('popen2: bad read dup\n') |
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1503 if os.dup(c2pwrite) <> 1: |
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1504 sys.stderr.write('popen2: bad write dup\n') |
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1505 for i in range(3, MAXFD): |
|
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1506 try: |
|
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1507 os.close(i) |
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1508 except: |
|
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1509 pass |
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1510 try: |
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1511 os.execv(cmd[0], cmd) |
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1512 finally: |
|
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1513 os._exit(1) |
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1514 os.close(p2cread) |
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1515 tochild = os.fdopen(p2cwrite, 'w') |
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1516 os.close(c2pwrite) |
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1517 fromchild = os.fdopen(c2pread, 'r') |
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1518 return fromchild, tochild |
|
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1519 |
|
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1520 Note that many interactive programs (e.g. vi) don't work well with |
|
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1521 pipes substituted for standard input and output. You will have to use |
|
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1522 pseudo ttys ("ptys") instead of pipes. There is some undocumented |
|
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|
1523 code to use these in the library module pty.py -- I'm afraid you're on |
| 2855 | 1524 your own here. |
| 1525 | |
| 1526 A different answer is a Python interface to Don Libes' "expect" | |
| 1527 library. A prerelease of this is available on the Python ftp mirror | |
| 1528 sites in the contrib subdirectory as expy-0.3.tar.gz, e.g. | |
| 1529 <URL:ftp://ftp.python.org/pub/python/contrib/expy-0.3.tar.gz>. | |
|
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1530 |
|
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1531 4.31. Q. How do I call a function if I have the arguments in a tuple? |
|
2660
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1532 |
|
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1533 A. Use the built-in function apply(). For instance, |
|
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1534 |
|
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1535 func(1, 2, 3) |
|
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1536 |
|
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|
1537 is equivalent to |
|
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1538 |
|
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1539 args = (1, 2, 3) |
|
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1540 apply(func, args) |
|
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1541 |
|
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|
1542 Note that func(args) is not the same -- it calls func() with exactly |
|
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|
1543 one argument, the tuple args, instead of three arguments, the integers |
|
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1544 1, 2 and 3. |
|
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1545 |
|
2716
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1546 4.32. Q. How do I enable font-lock-mode for Python in Emacs? |
|
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1547 |
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1548 A. Assuming you're already using python-mode and font-lock-mode |
|
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1549 separately, all you need to do is put this in your .emacs file: |
|
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1550 |
|
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1551 (defun my-python-mode-hook () |
|
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1552 (setq font-lock-keywords python-font-lock-keywords) |
|
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1553 (font-lock-mode 1)) |
|
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1554 (add-hook 'python-mode-hook 'my-python-mode-hook) |
|
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1555 |
|
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1556 4.33. Q. Is there an inverse to the format operator (a la C's scanf())? |
|
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1557 |
|
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1558 A. Not as such. |
|
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1559 |
|
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1560 For simple input parsing, the easiest approach is usually to split |
|
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1561 the line into whitespace-delimited words using string.split(), and to |
|
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1562 convert decimal strings to numeric values using string.atoi(), |
|
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1563 string.atol() or string.atof(). (Python's atoi() is 32-bit and its |
|
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1564 atol() is arbitrary precision.) If you want to use another delimiter |
|
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1565 than whitespace, use string.splitfield() (possibly combining it with |
|
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1566 string.strip() which removes surrounding whitespace from a string). |
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1567 |
|
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1568 For more complicated input parsing, regular expressions (see module |
|
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1569 regex) are better suited and more powerful than C's scanf(). |
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|
1570 |
| 1942 | 1571 |
| 1529 | 1572 5. Extending Python |
| 1573 =================== | |
| 1574 | |
| 1575 5.1. Q. Can I create my own functions in C? | |
| 1576 | |
| 1577 A. Yes, you can create built-in modules containing functions, | |
|
1541
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|
1578 variables, exceptions and even new types in C. This is explained in |
|
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|
1579 the document "Extending and Embedding the Python Interpreter" (the |
|
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1580 LaTeX file Doc/ext.tex). Also read the chapter on dynamic loading. |
| 1529 | 1581 |
| 1582 5.2. Q. Can I create my own functions in C++? | |
| 1583 | |
| 1584 A. Yes, using the C-compatibility features found in C++. Basically | |
| 1585 you place extern "C" { ... } around the Python include files and put | |
| 1586 extern "C" before each function that is going to be called by the | |
| 1587 Python interpreter. Global or static C++ objects with constructors | |
| 1588 are probably not a good idea. | |
| 1589 | |
| 1663 | 1590 5.3. Q. How can I execute arbitrary Python statements from C? |
| 1591 | |
| 1592 A. The highest-level function to do this is run_command() which takes | |
| 1593 a single string argument which is executed in the context of module | |
| 1594 __main__ and returns 0 for success and -1 when an exception occurred | |
| 1595 (including SyntaxError). If you want more control, use run_string(); | |
| 1596 see the source for run_command() in Python/pythonrun.c. | |
| 1597 | |
| 1598 5.4. Q. How can I evaluate an arbitrary Python expression from C? | |
| 1599 | |
| 1600 A. Call the function run_string() from the previous question with the | |
| 1601 start symbol eval_input; it then parses an expression, evaluates it | |
| 1602 and returns its value. See exec_eval() in Python/bltinmodule.c. | |
| 1603 | |
| 1604 5.5. Q. How do I extract C values from a Python object? | |
| 1605 | |
| 1606 A. That depends on the object's type. If it's a tuple, | |
| 1607 gettuplesize(o) returns its length and gettupleitem(o, i) returns its | |
| 1608 i'th item; similar for lists with getlistsize(o) and getlistitem(o, | |
| 1609 i). For strings, getstringsize(o) returns its length and | |
| 1610 getstringvalue(o) a pointer to its value (note that Python strings may | |
| 1611 contain null bytes so strlen() is not safe). To test which type an | |
| 1612 object is, first make sure it isn't NULL, and then use | |
| 1613 is_stringobject(o), is_tupleobject(o), is_listobject(o) etc. | |
| 1614 | |
| 1615 5.6. Q. How do I use mkvalue() to create a tuple of arbitrary length? | |
| 1616 | |
| 1617 A. You can't. Use t = newtupleobject(n) instead, and fill it with | |
| 1618 objects using settupleitem(t, i, o) -- note that this "eats" a | |
| 1619 reference count of o. Similar for lists with newlistobject(n) and | |
|
1903
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1620 setlistitem(l, i, o). Note that you *must* set all the tuple items to |
|
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|
1621 some value before you pass the tuple to Python code -- |
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1622 newtupleobject(n) initializes them to NULL, which isn't a valid Python |
|
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1623 value. |
|
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|
1624 |
|
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|
1625 5.7. Q. What happened to mktuple(), featured in an example in the |
|
1903
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|
1626 Extensions manual? |
|
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1627 |
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|
1628 A. It's a typo, I meant newtupleobject() (see previous question). |
|
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1629 |
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1630 5.8. Q. How do I call an object's method from C? |
|
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|
1631 |
|
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|
1632 A. Here's a function (untested) that might become part of the next |
|
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|
1633 release in some form. It uses <stdarg.h> to allow passing the |
|
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|
1634 argument list on to vmkvalue(): |
|
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|
1635 |
| 2048 | 1636 object *call_method(object *inst, char *methodname, char *format, ...) |
| 1637 { | |
| 1638 object *method; | |
| 1639 object *args; | |
| 1640 object *result; | |
| 1641 va_list va; | |
| 1642 method = getattr(inst, methodname); | |
| 1643 if (method == NULL) return NULL; | |
| 1644 va_start(va, format); | |
| 1645 args = vmkvalue(format, va); | |
| 1646 va_end(va); | |
| 1647 if (args == NULL) { | |
| 1648 DECREF(method); | |
| 1649 return NULL; | |
| 1650 } | |
| 1651 result = call_object(method, args); | |
| 1652 DECREF(method); | |
| 1653 DECREF(args); | |
| 1654 return result; | |
| 1655 } | |
|
1903
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1656 |
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|
1657 This works for any instance that has methods -- whether built-in or |
|
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|
1658 user-defined. You are responsible for eventually DECREF'ing the |
|
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|
1659 return value. |
|
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1660 |
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1661 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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|
1662 (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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|
1663 |
| 2048 | 1664 res = call_method(f, "seek", "(OO)", 10, 0); |
| 1665 if (res == NULL) { | |
| 1666 ... an exception occurred ... | |
| 1667 } | |
| 1668 else { | |
| 1669 DECREF(res); | |
| 1670 } | |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1671 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1672 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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|
1673 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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|
1674 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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|
1675 parentheses, e.g. "(i)". |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1676 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1677 5.9. Q. How do I catch the output from print_error()? |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1678 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1679 A. (Due to Mark Hammond): |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1680 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1681 * 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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|
1682 FWIW, there seems to be a small problem that requires the 'softspace' |
|
2526
d1123b10cf23
removed GPL mumbo jumbo
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|
1683 attribute to be defined too (fixed in 1.2). |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1684 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1685 * 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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|
1686 |
| 1942 | 1687 * call print_error, or just allow the standard traceback mechanism to |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1688 work. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1689 |
| 1942 | 1690 Then, the output will go wherever your write() method sends it. |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1691 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1692 5.10. Q. How do I access a module written in Python from C? |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1693 |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1694 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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|
1695 |
| 2048 | 1696 module = import_module("<modulename>"); |
|
1903
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1697 |
|
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|
1698 If the module hasn't been imported yet (i.e. it is not yet present in |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1699 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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|
1700 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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|
1701 the module into any namespace -- it only ensures it has been |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1702 initialized and is stored in sys.modules. |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1703 |
|
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|
1704 You can then access the module's attributes (i.e. any name defined in |
|
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1705 the module) as follows: |
|
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New version: 1.14 (previous oine was misnumbered 1.12).
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|
1706 |
| 2048 | 1707 attr = getattr(module, "<attrname>"); |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
1708 |
|
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|
1709 Calling setattr(), to assign to variables in the module, also works. |
| 1663 | 1710 |
|
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|
1711 5.11. Q. How do I interface to C++ objects from Python? |
|
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|
1712 |
|
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|
1713 A. Depending on your requirements, there are many approaches. Begin |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1714 by reading the "Extending and Embedding" document (Doc/ext.tex, see |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1715 also <URL:http://www.python.org/doc/>). Realize that for the Python |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1716 run-time system, there isn't a whole lot of difference between C and |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1717 C++ -- so the strategy to build a new Python type around a C structure |
|
87847228b158
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|
1718 (pointer) type will also work for C++ objects. |
|
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|
1719 |
|
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|
1720 Automatic generation of interfaces between Python and C++ is still at |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1721 the horizon -- parsing C++ header files requires an almost complete |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1722 C++ parser, and many features aren't easily translated from C++ to |
|
87847228b158
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|
1723 Python: certain forms of operator oveloading, function overloading |
|
87847228b158
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|
1724 (best approached by a varargs function which explicitly type-checks |
|
87847228b158
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|
1725 its arguments), and reference arguments are just a number of features |
|
87847228b158
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|
1726 that are hard to translate correctly if at all. |
|
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|
1727 |
|
87847228b158
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|
1728 The hardest problem is to transparently translate the C++ class |
|
87847228b158
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|
1729 hierarchy to Python, so that Python programs derive classes from C++ |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1730 classes. Given suitable constraints, this may be possible, but it |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1731 would require more space than I have in this FAQ to explain how. |
|
87847228b158
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|
1732 In any case, you can get quite a bit done without this, using just the |
|
87847228b158
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|
1733 existing classes from Python. |
|
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|
1734 |
|
87847228b158
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|
1735 If this all seems rather daunting, that may be because it is -- C++ |
|
87847228b158
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|
1736 isn't exactly a baby to handle without gloves! However, people have |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1737 accomplished amazing feats of interfacing between Python and C++, and |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1738 a detailed question posted to the Python list is likely to elicit some |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1739 interesting and useful responses. |
|
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|
1740 |
| 1529 | 1741 |
| 1742 6. Python's design | |
| 1743 ================== | |
| 1744 | |
|
3023
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|
1745 6.1. Q. Why isn't there a generic copying operation for objects in Python? |
| 1529 | 1746 |
|
3023
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|
1747 A. Historically, there wasn't. However, starting in Python 1.2, |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1748 there's a library module "copy" which supports both shallow and deep |
|
87847228b158
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|
1749 copying of most common Python objects (though not things like open |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1750 files, sockets or windows), including an extensible mechanism to copy |
|
87847228b158
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|
1751 class instances. |
| 1529 | 1752 |
| 1753 6.2. Q. Why isn't there a generic way to implement persistent objects | |
| 1754 in Python? (Persistent == automatically saved to and restored from | |
| 1755 disk.) | |
| 1756 | |
|
3023
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|
1757 A. Like the previous question, historically, there wasn't. The |
|
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|
1758 library module "pickle" now solves this in a very general way (though |
|
87847228b158
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|
1759 you still can't store things like open files, sockests or windows), |
|
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|
1760 and the library module "shelve" uses pickle and (g)dbm to create |
|
87847228b158
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|
1761 presistent mappings containing arbitrary Python objects. There are |
|
87847228b158
several new questions, 1.3 beta mentioned
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|
1762 some problems with shelve when using gdbm which will be solved in |
|
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|
1763 Python 1.3. |
|
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|
1764 |
| 1529 | 1765 6.3. Q. Why isn't there a switch or case statement in Python? |
| 1766 | |
| 1767 A. You can do this easily enough with a sequence of | |
| 1768 if... elif... elif... else. There have been some proposals for switch | |
| 1942 | 1769 statement syntax, but there is no consensus (yet) on whether and how |
| 1529 | 1770 to do range tests. |
| 1771 | |
|
1657
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|
1772 6.4. Q. Why does Python use indentation for grouping of statements? |
|
f02a46754f50
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|
1773 |
|
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|
1774 A. Basically I believe that using indentation for grouping is |
|
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1775 extremely elegant and contributes a lot to the clarity of the average |
|
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|
1776 Python program. Most people learn to love this feature after a while. |
|
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|
1777 Some arguments for it: |
|
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|
1778 |
|
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|
1779 - Since there are no begin/end brackets there cannot be a disagreement |
|
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|
1780 between grouping perceived by the parser and the human reader. I |
|
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|
1781 remember long ago seeing a C fragment like this: |
|
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|
1782 |
| 2048 | 1783 if (x <= y) |
| 1784 x++; | |
| 1785 y--; | |
| 1786 z++; | |
|
1657
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|
1787 |
|
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|
1788 and staring a long time at it wondering why y was being decremented |
|
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|
1789 even for x > y... (And I wasn't a C newbie then either.) |
|
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|
1790 |
|
2716
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|
1791 - Since there are no begin/end brackets, Python is much less prone to |
|
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|
1792 coding-style conflicts. In C there are loads of different ways to |
|
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|
1793 place the braces (including the choice whether to place braces around |
|
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|
1794 single statements in certain cases, for consistency). If you're used |
|
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|
1795 to reading (and writing) code that uses one style, you will feel at |
|
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|
1796 least slightly uneasy when reading (or being required to write) |
|
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|
1797 another style. |
|
1657
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|
1798 |
|
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1799 - Many coding styles place begin/end brackets on a line by themself. |
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1800 This makes programs considerably longer and wastes valuable screen |
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1801 space, making it harder to get a good overview over a program. |
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1802 Ideally, a function should fit on one basic tty screen (say, 20 |
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1803 lines). 20 lines of Python are worth a LOT more than 20 lines of C. |
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1804 This is not solely due to the lack of begin/end brackets (the lack of |
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1805 declarations also helps, and the powerful operations of course), but |
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1806 it certainly helps! |
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1807 |
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1808 6.5. Q. Why are Python strings immutable? |
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1809 |
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1810 A. There are two advantages. One is performance: knowing that a |
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1811 string is immutable makes it easy to lay it out at construction time |
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1812 -- fixed and unchanging storage requirements. (This is also one of |
| 1942 | 1813 the reasons for the distinction between tuples and lists.) The |
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1814 other is that strings in Python are considered as "elemental" as |
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1815 numbers. No amount of activity will change the value 8 to anything |
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1816 else, and in Python, no amount of activity will change the string |
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1817 "eight" to anything else. (Adapted from Jim Roskind) |
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1818 |
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1819 6.6. Q. Why don't strings have methods like index() or sort(), like |
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1820 lists? |
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1821 |
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1822 A. Good question. Strings currently don't have methods at all |
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1823 (likewise tuples and numbers). Long ago, it seemed unnecessary to |
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1824 implement any of these functions in C, so a standard library module |
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1825 "string" written in Python was created that performs string related |
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1826 operations. Since then, the cry for performance has moved most of |
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1827 them into the built-in module strop (this is imported by module |
|
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1828 string, which is still the preferred interface, without loss of |
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1829 performance except during initialization). Some of these functions |
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1830 (e.g. index()) could easily be implemented as string methods instead, |
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1831 but others (e.g. sort()) can't, since their interface prescribes that |
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1832 they modify the object, while strings are immutable (see the previous |
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1833 question). |
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1834 |
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1835 6.7. Q. Why does Python use methods for some functionality |
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1836 (e.g. list.index()) but functions for other (e.g. len(list))? |
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1837 |
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1838 A. Functions are used for those operations that are generic for a |
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1839 group of types and which should work even for objects that don't have |
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1840 methods at all (e.g. numbers, strings, tuples). Also, implementing |
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1841 len(), max(), min() as a built-in function is actually less code than |
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1842 implementing them as methods for each type. One can quibble about |
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1843 individual cases but it's really too late to change such things |
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1844 fundamentally now. |
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1845 |
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1846 6.8. Q. Why can't I derive a class from built-in types (e.g. lists or |
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1847 files)? |
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1848 |
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1849 A. This is caused by the relatively late addition of (user-defined) |
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1850 classes to the language -- the implementation framework doesn't easily |
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1851 allow it. See the answer to question 4.2 for a work-around. This |
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1852 *may* be fixed in the (distant) future. |
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1853 |
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1854 6.9. Q. Why must 'self' be declared and used explicitly in method |
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1855 definitions and calls? |
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1856 |
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1857 A. By asking this question you reveal your C++ background. :-) |
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1858 When I added classes, this was (again) the simplest way of |
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1859 implementing methods without too many changes to the interpreter. I |
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1860 borrowed the idea from Modula-3. It turns out to be very useful, for |
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1861 a variety of reasons. |
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1862 |
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1863 First, it makes it more obvious that you are using a method or |
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1864 instance attribute instead of a local variable. Reading "self.x" or |
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1865 "self.meth()" makes it absolutely clear that an instance variable or |
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1866 method is used even if you don't know the class definition by heart. |
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1867 In C++, you can sort of tell by the lack of a local variable |
| 1942 | 1868 declaration (assuming globals are rare or easily recognizable) -- but |
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1869 in Python, there are no local variable declarations, so you'd have to |
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1870 look up the class definition to be sure. |
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1871 |
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1872 Second, it means that no special syntax is necessary if you want to |
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1873 explicitly reference or call the method from a particular class. In |
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1874 C++, if you want to use a method from base class that is overridden in |
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1875 a derived class, you have to use the :: operator -- in Python you can |
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1876 write baseclass.methodname(self, <argument list>). This is |
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1877 particularly useful for __init__() methods, and in general in cases |
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1878 where a derived class method wants to extend the base class method of |
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1879 the same name and thus has to call the base class method somehow. |
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1880 |
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1881 Lastly, for instance variables, it solves a syntactic problem with |
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1882 assignment: since local variables in Python are (by definition!) those |
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1883 variables to which a value assigned in a function body (and that |
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1884 aren't explicitly declared global), there has to be some way to tell |
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1885 the interpreter that an assignment was meant to assign to an instance |
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1886 variable instead of to a local variable, and it should preferably be |
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1887 syntactic (for efficiency reasons). C++ does this through |
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1888 declarations, but Python doesn't have declarations and it would be a |
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1889 pity having to introduce them just for this purpose. Using the |
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1890 explicit "self.var" solves this nicely. Similarly, for using instance |
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1891 variables, having to write "self.var" means that references to |
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1892 unqualified names inside a method don't have to search the instance's |
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1893 directories. |
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1894 |
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1895 6.10. Q. Can't you emulate threads in the interpreter instead of |
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1896 relying on an OS-specific thread implementation? |
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1897 |
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1898 A. Unfortunately, the interpreter pushes at least one C stack frame |
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1899 for each Python stack frame. Also, extensions can call back into |
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1900 Python at almost random moments. Therefore a complete threads |
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1901 implementation requires thread support for C. |
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1902 |
| 1942 | 1903 6.11. Q. Why can't lambda forms contain statements? |
| 1904 | |
| 1905 A. Python lambda forms cannot contain statements because Python's | |
|
2208
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1906 syntactic framework can't handle statements nested inside expressions. |
| 1942 | 1907 |
| 1908 However, in Python, this is not a serious problem. Unlike lambda | |
| 1909 forms in other languages, where they add functionality, Python lambdas | |
| 1910 are only a shorthand notation if you're too lazy to define a function. | |
| 1911 | |
| 1912 Functions are already first class objects in Python, and can be | |
| 1913 declared in a local scope. Therefore the only advantage of using a | |
| 1914 lambda form instead of a locally-defined function is that you'll have | |
| 1915 to invent a name for the function -- but that's just a local variable | |
| 1916 to which the function object (which is exactly the same type of object | |
| 1917 that a lambda form yields) is assigned! | |
| 1918 | |
| 1919 6.12. Q. Why is there no more efficient way of iterating over a dictionary | |
| 1920 than first constructing the list of keys()? | |
| 1921 | |
| 1922 A. Have you tried it? I bet it's fast enough for your purposes! In | |
| 1923 most cases such a list takes only a few percent of the space occupied | |
| 1924 by the dictionary -- it needs only 4 bytes (the size of a pointer) per | |
| 1925 key -- a dictionary costs 8 bytes per key plus between 30 and 70 | |
| 1926 percent hash table overhead, plus the space for the keys and values -- | |
| 1927 by necessity all keys are unique objects and a string object (the most | |
| 1928 common key type) costs at least 18 bytes plus the length of the | |
| 1929 string. Add to that the values contained in the dictionary, and you | |
| 1930 see that 4 bytes more per item really isn't that much more memory... | |
| 1931 | |
| 1932 A call to dict.keys() makes one fast scan over the dictionary | |
| 1933 (internally, the iteration function does exist) copying the pointers | |
| 1934 to the key objects into a pre-allocated list object of the right size. | |
| 1935 The iteration time isn't lost (since you'll have to iterate anyway -- | |
| 1936 unless in the majority of cases your loop terminates very prematurely | |
| 1937 (which I doubt since you're getting the keys in random order). | |
| 1938 | |
| 1939 I don't expose the dictionary iteration operation to Python | |
| 1940 programmers because the dictionary shouldn't be modified during the | |
| 1941 entire iteration -- if it is, there's a very small chance that the | |
| 1942 dictionary is reorganized because the hash table becomes too full, and | |
| 1943 then the iteration may miss some items and see others twice. Exactly | |
| 1944 because this only occurs rarely, it would lead to hidden bugs in | |
| 1945 programs: it's easy never to have it happen during test runs if you | |
| 1946 only insert or delete a few items per iteration -- but your users will | |
| 1947 surely hit upon it sooner or later. | |
| 1948 | |
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1949 6.13. Q. Can Python be compiled to machine code, C or some other language? |
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1950 |
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1951 A. Not easily. Python's high level data types, dynamic typing of |
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1952 objects and run-time invocation of the interpreter (using eval() or |
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1953 exec) together mean that a "compiled" Python program would probably |
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1954 consist mostly of calls into the Python run-time system, even for |
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1955 seemingly simple operations like "x+1". Thus, the performance gain |
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1956 would probably be minimal. |
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1957 |
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1958 Internally, Python source code is always translated into a "virtual |
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1959 machine code" or "byte code" representation before it is interpreted |
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1960 (by the "Python virtual machine" or "bytecode interpreter"). In order |
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1961 to avoid the overhead of parsing and translating modules that rarely |
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1962 change over and over again, this byte code is written on a file whose |
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1963 name ends in ".pyc" whenever a module is parsed (from a file whose |
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1964 name ends in ".py"). When the corresponding .py file is changed, it |
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1965 is parsed and translated again and the .pyc file is rewritten. There |
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1966 is no performance difference once the .pyc file has been loaded (the |
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1967 bytecode read from the .pyc file is exactly the same as the bytecode |
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1968 created by direct translation). The only difference is that loading |
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1969 code from a .pyc file is faster than parsing and translating a .py |
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1970 file, so the presence of precompiled .pyc files will generally improve |
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1971 start-up time of Python scripts. If desired, the Lib/compileall.py |
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1972 module/script can be used to force creation of valid .pyc files for a |
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1973 given set of modules. |
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1974 |
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1975 If you are looking for a way to translate Python programs in order to |
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1976 distribute them in binary form, without the need to distribute the |
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1977 interpreter and library as well, have a look at the freeze.py script |
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1978 in the Tools/freeze directory. This creates a single binary file |
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1979 incorporating your program, the Python interpreter, and those parts of |
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1980 the Python library that are needed by your program. Of course, the |
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1981 resulting binary will only run on the same type of platform as that |
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1982 used to create it. |
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1983 |
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1984 Hints for proper usage of freeze.py: |
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1985 |
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1986 - the script must be in a file whose name ends in .py |
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1987 |
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1988 - you must have installed Python fully: |
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1989 |
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1990 make install |
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1991 make libinstall |
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1992 make inclinstall |
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1993 make libainstall |
|
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1994 |
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1995 6.14. Q. Why doesn't Python use proper garbage collection? |
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1996 |
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1997 A. It's looking less and less likely that Python will ever get |
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1998 "automatic" garbage collection (GC). For one thing, unless this were |
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1999 added to C as a standard feature, it's a portability pain in the ass. |
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2000 And yes, I know about the Xerox library. It has bits of assembler |
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2001 code for *most* *common* platforms. Not for all. And although it is |
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2002 mostly transparent, it isn't completely transparent (when I once |
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2003 linked Python with it, it dumped core). |
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2004 |
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2005 "Proper" GC also becomes a problem when Python gets embedded into |
|
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2006 other applications. While in a stand-alone Python it may be fine to |
|
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2007 replace the standard malloc() and free() with versions provided by the |
|
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2008 GC library, an application embedding Python may want to have its *own* |
|
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2009 substitute for malloc() and free(), and may not want Python's. Right |
|
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2010 now, Python works with anything that implements malloc() and free() |
|
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2011 properly. |
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2012 |
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2013 Besides, the predictability of destructor calls in Python is kind of |
|
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2014 attractive. With GC, the following code (which is fine in current |
|
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2015 Python) will run out of file descriptors long before it runs out of |
|
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2016 memory: |
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2017 |
|
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2018 for file in <very long list of files>: |
|
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2019 f = open(file) |
|
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2020 c = file.read(1) |
|
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2021 |
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2022 Using the current reference counting and destructor scheme, each new |
|
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2023 assignment to f closes the previous file. Using GC, this is not |
|
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2024 guaranteed. Sure, you can think of ways to fix this. But it's not |
|
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2025 off-the-shelf technology. |
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2026 |
| 1529 | 2027 |
| 2028 7. Using Python on non-UNIX platforms | |
| 2029 ===================================== | |
| 2030 | |
|
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2031 7.1. Q. Is there a Mac version of Python? |
| 1529 | 2032 |
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2033 A. Yes, see the "mac" subdirectory of the distribution sites, |
|
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2034 e.g. <URL:ftp://ftp.python.org/pub/python/mac/>. |
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2035 |
|
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2036 7.2. Q. Is there a DOS version of Python? |
| 1529 | 2037 |
|
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2038 A. Yes, see the "pc" subdirectory of the distribution sites, |
|
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2039 e.g. <URL:ftp://ftp.python.org/pub/python/pc/>. |
|
1903
e450bd43631a
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2040 |
|
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2041 7.3. Q. Is there a Windows 3.1(1) version of Python? |
| 1529 | 2042 |
|
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2043 A. Yes, also see the "pc" subdirectory of the distribution sites, |
| 2855 | 2044 e.g. <URL:ftp://ftp.python.org/pub/python/pc/>. You may also be able |
| 2045 to run either of the Windows NT versions (see next question) if you | |
| 2046 have Microsoft's "win32s". | |
|
1903
e450bd43631a
New version: 1.14 (previous oine was misnumbered 1.12).
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|
2047 |
|
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2048 7.4. Q. Is there a Windows NT version of Python? |
|
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2049 |
| 2855 | 2050 A. There are two, both sporting DLL support for dynamic loading of |
| 2051 Python modules, and extensions to access the Win32 GUI API. | |
| 2052 | |
| 2053 Mark Hammond <MHammond@cmutual.com.au> maintains an NT port which | |
| 2054 includes an interface to the Microsoft Foundation Classes and a Python | |
| 2055 programming environment using it that's written mostly in Python. See | |
| 2056 <URL:ftp://ftp.python.org/pub/python/nt/>. | |
| 2057 | |
| 2058 Jim Ahlstrom's WPY portable GUI runs on Windows NT and is modeled | |
| 2059 after the Microsoft Foundation Classes. Source and binaries are | |
| 2060 available in <URL:ftp://ftp.python.org/pub/python/wpy>. | |
|
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2061 |
| 2048 | 2062 Sam Rushing <rushing@squirl.oau.org> once announced he knows how to |
| 2063 build Python for the Windows NT on the DEC Alpha AXP. | |
| 1942 | 2064 |
| 2065 Note that currently there is no unified compilation environment for | |
| 2066 all NT platforms -- hopefully Microsoft will fix this with the release | |
| 2067 of Visual C++ 2.0. | |
| 2068 | |
|
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|
2069 7.5. Q. Is there a Windows 95 version of Python? |
| 1663 | 2070 |
| 2855 | 2071 A. The Windows NT versions might work, otherwise the Windows 3.1(1) |
|
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|
2072 version should work (isn't Windows 95 supposed to be backwards |
|
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|
2073 compatible?). |
|
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|
2074 |
|
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|
2075 7.6. Q. Is there an OS/2 version of Python? |
| 1663 | 2076 |
|
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2077 A. Yes, also see the "pc" subdirectory of the distribution sites, |
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2078 e.g. <URL:ftp://ftp.python.org/pub/python/pc/>. |
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2079 |
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2080 7.7. Q. Is there a VMS version of Python? |
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2081 |
| 2855 | 2082 A. Donn Cave <donn@cac.washington.edu> did a partial port. The |
| 2083 results of his efforts are on public display in | |
| 3018 | 2084 <<URL:ftp://ftp.python.org/pub/python/contrib/vms.tar.gz/>. Someone |
| 2085 else is working on a more complete port, for details watch the list. | |
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2086 |
| 2855 | 2087 7.8. Q. What about IBM mainframes, or other non-UNIX platforms? |
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2088 |
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2089 A. I haven't heard about these, except I remember hearing about an |
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2090 OS/9 port and a port to Vxworks (both operating systems for embedded |
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2091 systems). If you're interested in any of this, go directly to the |
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2092 newsgroup and ask there, you may find exactly what you need. For |
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2093 example, a port to MPE/iX 5.0 on HP3000 computers was just announced, |
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2094 see <URL:http://www.allegro.com/software/>. |
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2095 |
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2096 7.9. Q. Where are the source or Makefiles for the non-UNIX versions? |
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2097 |
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2098 A. The standard sources can (almost) be used. Additional sources can |
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2099 be found in the platform-specific subdirectories of the distribution. |
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2100 |
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2101 7.10. Q. What is the status and support for the non-UNIX versions? |
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2102 |
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2103 A. I don't have access to most of these platforms, so in general I am |
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2104 dependent on material submitted by volunteers(*). However I strive to |
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2105 integrate all changes needed to get it to compile on a particular |
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2106 platform back into the standard sources, so porting of the next |
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2107 version to the various non-UNIX platforms should be easy. |
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2108 |
| 2048 | 2109 (*) For the Macintosh, that volunteer is me, with help from Jack |
| 2110 Jansen <jack@cwi.nl>. | |
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2111 |
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2112 7.11. Q. I have a PC version but it appears to be only a binary. |
| 1663 | 2113 Where's the library? |
| 1529 | 2114 |
| 2115 A. You still need to copy the files from the distribution directory | |
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2116 "python/Lib" to your system. If you don't have the full distribution, |
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2117 you can get the file lib<version>.tar.gz from most ftp sites carrying |
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2118 Python; this is a subset of the distribution containing just those |
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2119 files, e.g. <URL:ftp://ftp.python.org/pub/python/src/lib1.1.tar.gz>. |
| 1529 | 2120 |
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2121 Once you have installed the library, you need to point sys.path to it. |
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2122 Assuming the library is in C:\misc\python\lib, the following commands |
|
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2123 will point your Python interpreter to it (note the doubled backslashes |
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2124 -- you can also use single forward slashes instead): |
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2125 |
| 2048 | 2126 >>> import sys |
| 2127 >>> sys.path.insert(0, 'C:\\misc\\python\\lib') | |
| 2128 >>> | |
|
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2129 |
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2130 For a more permanent effect, set the environment variable PYTHONPATH, |
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2131 as follows (talking to a DOS prompt): |
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2132 |
| 2048 | 2133 C> SET PYTHONPATH=C:\misc\python\lib |
|
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2134 |
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2135 7.12. Q. Where's the documentation for the Mac or PC version? |
| 1529 | 2136 |
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2137 A. The documentation for the Unix version also applies to the Mac and |
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2138 PC versions. Where applicable, differences are indicated in the text. |
| 1529 | 2139 |
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2140 7.13. Q. The Mac (PC) version doesn't seem to have any facilities for |
|
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2141 creating or editing programs apart from entering it interactively, and |
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2142 there seems to be no way to save code that was entered interactively. |
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2143 How do I create a Python program on the Mac (PC)? |
| 1529 | 2144 |
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2145 A. Use an external editor. On the Mac, BBEdit seems to be a popular |
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2146 no-frills text editor. I work like this: start the interpreter; edit |
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2147 a module file using BBedit; import and test it in the interpreter; |
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2148 edit again in BBedit; then use the built-in function reload() to |
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2149 re-read the imported module; etc. |
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2150 |
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2151 Regarding the same question for the PC, Kurt Wm. Hemr writes: "While |
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2152 anyone with a pulse could certainly figure out how to do the same on |
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2153 MS-Windows, I would recommend the NotGNU Emacs clone for MS-Windows. |
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2154 Not only can you easily resave and "reload()" from Python after making |
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2155 changes, but since WinNot auto-copies to the clipboard any text you |
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2156 select, you can simply select the entire procedure (function) which |
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2157 you changed in WinNot, switch to QWPython, and shift-ins to reenter |
|
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2158 the changed program unit." |