Mercurial > cpython-lru_cache-weakref
annotate Doc/lib/libimp.tex @ 25838:8540887bcec6 2.2
Backport of 2.183:
Fix memory leak in add_subclass() found by NealN with valgrind.
| author | Guido van Rossum <guido@python.org> |
|---|---|
| date | Fri, 18 Oct 2002 13:42:21 +0000 |
| parents | e1423ec9e6ec |
| children |
| rev | line source |
|---|---|
| 8918 | 1 \section{\module{imp} --- |
| 10699 | 2 Access the \keyword{import} internals} |
| 3 | |
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4 \declaremodule{builtin}{imp} |
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5 \modulesynopsis{Access the implementation of the \keyword{import} statement.} |
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6 |
| 2110 | 7 |
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8 This\stindex{import} module provides an interface to the mechanisms |
| 10699 | 9 used to implement the \keyword{import} statement. It defines the |
| 10 following constants and functions: | |
| 2110 | 11 |
| 12 | |
| 13 \begin{funcdesc}{get_magic}{} | |
| 8935 | 14 \indexii{file}{byte-code} |
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15 Return the magic string value used to recognize byte-compiled code |
| 8935 | 16 files (\file{.pyc} files). (This value may be different for each |
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17 Python version.) |
| 2110 | 18 \end{funcdesc} |
| 19 | |
| 20 \begin{funcdesc}{get_suffixes}{} | |
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21 Return a list of triples, each describing a particular type of module. |
| 2110 | 22 Each triple has the form \code{(\var{suffix}, \var{mode}, |
| 23 \var{type})}, where \var{suffix} is a string to be appended to the | |
| 24 module name to form the filename to search for, \var{mode} is the mode | |
| 8935 | 25 string to pass to the built-in \function{open()} function to open the |
| 26 file (this can be \code{'r'} for text files or \code{'rb'} for binary | |
| 2110 | 27 files), and \var{type} is the file type, which has one of the values |
| 7606 | 28 \constant{PY_SOURCE}, \constant{PY_COMPILED}, or |
| 29 \constant{C_EXTENSION}, described below. | |
| 2110 | 30 \end{funcdesc} |
| 31 | |
| 7038 | 32 \begin{funcdesc}{find_module}{name\optional{, path}} |
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33 Try to find the module \var{name} on the search path \var{path}. If |
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34 \var{path} is a list of directory names, each directory is searched |
| 7606 | 35 for files with any of the suffixes returned by \function{get_suffixes()} |
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36 above. Invalid names in the list are silently ignored (but all list |
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37 items must be strings). If \var{path} is omitted or \code{None}, the |
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38 list of directory names given by \code{sys.path} is searched, but |
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39 first it searches a few special places: it tries to find a built-in |
| 7606 | 40 module with the given name (\constant{C_BUILTIN}), then a frozen module |
| 41 (\constant{PY_FROZEN}), and on some systems some other places are looked | |
| 42 in as well (on the Mac, it looks for a resource (\constant{PY_RESOURCE}); | |
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43 on Windows, it looks in the registry which may point to a specific |
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44 file). |
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45 |
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46 If search is successful, the return value is a triple |
| 2110 | 47 \code{(\var{file}, \var{pathname}, \var{description})} where |
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48 \var{file} is an open file object positioned at the beginning, |
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49 \var{pathname} is the pathname of the |
| 2110 | 50 file found, and \var{description} is a triple as contained in the list |
| 7606 | 51 returned by \function{get_suffixes()} describing the kind of module found. |
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52 If the module does not live in a file, the returned \var{file} is |
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53 \code{None}, \var{filename} is the empty string, and the |
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54 \var{description} tuple contains empty strings for its suffix and |
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55 mode; the module type is as indicate in parentheses above. If the |
| 7606 | 56 search is unsuccessful, \exception{ImportError} is raised. Other |
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57 exceptions indicate problems with the arguments or environment. |
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58 |
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59 This function does not handle hierarchical module names (names |
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60 containing dots). In order to find \var{P}.\var{M}, that is, submodule |
| 7606 | 61 \var{M} of package \var{P}, use \function{find_module()} and |
| 62 \function{load_module()} to find and load package \var{P}, and then use | |
| 63 \function{find_module()} with the \var{path} argument set to | |
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64 \code{\var{P}.__path__}. When \var{P} itself has a dotted name, apply |
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65 this recipe recursively. |
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66 \end{funcdesc} |
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67 |
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68 \begin{funcdesc}{load_module}{name, file, filename, description} |
| 7606 | 69 Load a module that was previously found by \function{find_module()} (or by |
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70 an otherwise conducted search yielding compatible results). This |
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71 function does more than importing the module: if the module was |
| 7606 | 72 already imported, it is equivalent to a |
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73 \function{reload()}\bifuncindex{reload}! The \var{name} argument |
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74 indicates the full module name (including the package name, if this is |
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75 a submodule of a package). The \var{file} argument is an open file, |
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76 and \var{filename} is the corresponding file name; these can be |
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77 \code{None} and \code{''}, respectively, when the module is not being |
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78 loaded from a file. The \var{description} argument is a tuple, as |
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79 would be returned by \function{get_suffixes()}, describing what kind |
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80 of module must be loaded. |
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81 |
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82 If the load is successful, the return value is the module object; |
| 7606 | 83 otherwise, an exception (usually \exception{ImportError}) is raised. |
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84 |
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85 \strong{Important:} the caller is responsible for closing the |
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86 \var{file} argument, if it was not \code{None}, even when an exception |
| 7606 | 87 is raised. This is best done using a \keyword{try} |
| 88 ... \keyword{finally} statement. | |
| 2110 | 89 \end{funcdesc} |
| 90 | |
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91 \begin{funcdesc}{new_module}{name} |
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92 Return a new empty module object called \var{name}. This object is |
| 7038 | 93 \emph{not} inserted in \code{sys.modules}. |
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94 \end{funcdesc} |
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95 |
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96 \begin{funcdesc}{lock_held}{} |
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97 Return 1 if the import lock is currently held, else 0. |
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98 On platforms without threads, always return 0. |
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99 |
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100 On platforms with threads, a thread executing an import holds an internal |
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101 lock until the import is complete. |
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102 This lock blocks other threads from doing an import until the original |
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103 import completes, which in turn prevents other threads from seeing |
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104 incomplete module objects constructed by the original thread while in |
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105 the process of completing its import (and the imports, if any, |
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106 triggered by that). |
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107 \end{funcdesc} |
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108 |
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109 The following constants with integer values, defined in this module, |
| 7606 | 110 are used to indicate the search result of \function{find_module()}. |
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111 |
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112 \begin{datadesc}{PY_SOURCE} |
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113 The module was found as a source file. |
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114 \end{datadesc} |
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115 |
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116 \begin{datadesc}{PY_COMPILED} |
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117 The module was found as a compiled code object file. |
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118 \end{datadesc} |
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119 |
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120 \begin{datadesc}{C_EXTENSION} |
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121 The module was found as dynamically loadable shared library. |
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122 \end{datadesc} |
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123 |
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124 \begin{datadesc}{PY_RESOURCE} |
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125 The module was found as a Macintosh resource. This value can only be |
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126 returned on a Macintosh. |
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127 \end{datadesc} |
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128 |
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129 \begin{datadesc}{PKG_DIRECTORY} |
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130 The module was found as a package directory. |
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131 \end{datadesc} |
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132 |
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133 \begin{datadesc}{C_BUILTIN} |
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134 The module was found as a built-in module. |
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135 \end{datadesc} |
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136 |
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137 \begin{datadesc}{PY_FROZEN} |
| 7606 | 138 The module was found as a frozen module (see \function{init_frozen()}). |
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139 \end{datadesc} |
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140 |
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141 The following constant and functions are obsolete; their functionality |
| 7606 | 142 is available through \function{find_module()} or \function{load_module()}. |
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143 They are kept around for backward compatibility: |
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144 |
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145 \begin{datadesc}{SEARCH_ERROR} |
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146 Unused. |
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147 \end{datadesc} |
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148 |
| 2110 | 149 \begin{funcdesc}{init_builtin}{name} |
| 150 Initialize the built-in module called \var{name} and return its module | |
| 151 object. If the module was already initialized, it will be initialized | |
| 7038 | 152 \emph{again}. A few modules cannot be initialized twice --- attempting |
| 7606 | 153 to initialize these again will raise an \exception{ImportError} |
| 154 exception. If there is no | |
| 2110 | 155 built-in module called \var{name}, \code{None} is returned. |
| 156 \end{funcdesc} | |
| 157 | |
| 158 \begin{funcdesc}{init_frozen}{name} | |
| 159 Initialize the frozen module called \var{name} and return its module | |
| 160 object. If the module was already initialized, it will be initialized | |
| 7038 | 161 \emph{again}. If there is no frozen module called \var{name}, |
| 2110 | 162 \code{None} is returned. (Frozen modules are modules written in |
| 163 Python whose compiled byte-code object is incorporated into a | |
| 7606 | 164 custom-built Python interpreter by Python's \program{freeze} utility. |
| 165 See \file{Tools/freeze/} for now.) | |
| 2110 | 166 \end{funcdesc} |
| 167 | |
| 168 \begin{funcdesc}{is_builtin}{name} | |
| 7606 | 169 Return \code{1} if there is a built-in module called \var{name} which |
| 170 can be initialized again. Return \code{-1} if there is a built-in | |
| 171 module called \var{name} which cannot be initialized again (see | |
| 172 \function{init_builtin()}). Return \code{0} if there is no built-in | |
| 173 module called \var{name}. | |
| 2110 | 174 \end{funcdesc} |
| 175 | |
| 176 \begin{funcdesc}{is_frozen}{name} | |
| 7606 | 177 Return \code{1} if there is a frozen module (see |
| 178 \function{init_frozen()}) called \var{name}, or \code{0} if there is | |
| 179 no such module. | |
| 2110 | 180 \end{funcdesc} |
| 181 | |
| 7038 | 182 \begin{funcdesc}{load_compiled}{name, pathname, file} |
| 8935 | 183 \indexii{file}{byte-code} |
| 2110 | 184 Load and initialize a module implemented as a byte-compiled code file |
| 185 and return its module object. If the module was already initialized, | |
| 7038 | 186 it will be initialized \emph{again}. The \var{name} argument is used |
| 2110 | 187 to create or access a module object. The \var{pathname} argument |
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188 points to the byte-compiled code file. The \var{file} |
| 2110 | 189 argument is the byte-compiled code file, open for reading in binary |
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190 mode, from the beginning. |
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191 It must currently be a real file object, not a |
| 2110 | 192 user-defined class emulating a file. |
| 193 \end{funcdesc} | |
| 194 | |
| 7038 | 195 \begin{funcdesc}{load_dynamic}{name, pathname\optional{, file}} |
| 2110 | 196 Load and initialize a module implemented as a dynamically loadable |
| 197 shared library and return its module object. If the module was | |
| 7038 | 198 already initialized, it will be initialized \emph{again}. Some modules |
| 2110 | 199 don't like that and may raise an exception. The \var{pathname} |
| 200 argument must point to the shared library. The \var{name} argument is | |
| 201 used to construct the name of the initialization function: an external | |
| 7606 | 202 C function called \samp{init\var{name}()} in the shared library is |
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203 called. The optional \var{file} argument is ignored. (Note: using |
| 2110 | 204 shared libraries is highly system dependent, and not all systems |
| 205 support it.) | |
| 206 \end{funcdesc} | |
| 207 | |
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208 \begin{funcdesc}{load_source}{name, pathname, file} |
| 2110 | 209 Load and initialize a module implemented as a Python source file and |
| 210 return its module object. If the module was already initialized, it | |
| 7038 | 211 will be initialized \emph{again}. The \var{name} argument is used to |
| 2110 | 212 create or access a module object. The \var{pathname} argument points |
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213 to the source file. The \var{file} argument is the source |
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214 file, open for reading as text, from the beginning. |
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215 It must currently be a real file |
| 2110 | 216 object, not a user-defined class emulating a file. Note that if a |
| 8935 | 217 properly matching byte-compiled file (with suffix \file{.pyc} or |
| 218 \file{.pyo}) exists, it will be used instead of parsing the given | |
| 219 source file. | |
| 2110 | 220 \end{funcdesc} |
| 221 | |
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222 |
| 2110 | 223 \subsection{Examples} |
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224 \label{examples-imp} |
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225 |
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226 The following function emulates what was the standard import statement |
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227 up to Python 1.4 (no hierarchical module names). (This |
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228 \emph{implementation} wouldn't work in that version, since |
| 7606 | 229 \function{find_module()} has been extended and |
| 230 \function{load_module()} has been added in 1.4.) | |
| 2110 | 231 |
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232 \begin{verbatim} |
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233 import imp |
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234 import sys |
| 2110 | 235 |
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236 def __import__(name, globals=None, locals=None, fromlist=None): |
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237 # Fast path: see if the module has already been imported. |
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238 try: |
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239 return sys.modules[name] |
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240 except KeyError: |
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241 pass |
| 2110 | 242 |
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243 # If any of the following calls raises an exception, |
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244 # there's a problem we can't handle -- let the caller handle it. |
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245 |
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246 fp, pathname, description = imp.find_module(name) |
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247 |
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248 try: |
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249 return imp.load_module(name, fp, pathname, description) |
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250 finally: |
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251 # Since we may exit via an exception, close fp explicitly. |
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252 if fp: |
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253 fp.close() |
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254 \end{verbatim} |
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255 |
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256 A more complete example that implements hierarchical module names and |
| 7606 | 257 includes a \function{reload()}\bifuncindex{reload} function can be |
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258 found in the module \module{knee}\refmodindex{knee}. |