# cpython-withatomic / Doc / libimp.tex

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