This module provides an interface to the mechanisms used to implement the
import statement. It defines the following constants and functions:
Return the magic string value used to recognize byte-compiled code files (
.pycfiles). (This value may be different for each Python version.)
Return a list of 3-element tuples, each describing a particular type of module. Each triple has the form
(suffix, mode, type), where suffix is a string to be appended to the module name to form the filename to search for, mode is the mode string to pass to the built-in
open()function to open the file (this can be
'r'for text files or
'rb'for binary files), and type is the file type, which has one of the values
C_EXTENSION, described below.
Try to find the module name. If path is omitted or
None, the list of directory names given by
sys.pathis searched, but first a few special places are searched: the function tries to find a built-in module with the given name (
C_BUILTIN), then a frozen module (
PY_FROZEN), and on some systems some other places are looked in as well (on Windows, it looks in the registry which may point to a specific file).
Otherwise, path must be a list of directory names; each directory is searched for files with any of the suffixes returned by
get_suffixes()above. Invalid names in the list are silently ignored (but all list items must be strings).
If search is successful, the return value is a 3-element tuple
(file, pathname, description):
file is an open file object positioned at the beginning, pathname is the pathname of the file found, and description is a 3-element tuple as contained in the list returned by
get_suffixes()describing the kind of module found.
If the module does not live in a file, the returned file is
None, pathname is the empty string, and the description tuple contains empty strings for its suffix and mode; the module type is indicated as given in parentheses above. If the search is unsuccessful,
ImportErroris raised. Other exceptions indicate problems with the arguments or environment.
If the module is a package, file is
None, pathname is the package path and the last item in the description tuple is
This function does not handle hierarchical module names (names containing dots). In order to find P.M, that is, submodule M of package P, use
load_module()to find and load package P, and then use
find_module()with the path argument set to
P.__path__. When P itself has a dotted name, apply this recipe recursively.
load_module(name, file, pathname, description)¶
Load a module that was previously found by
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
reload()! The name argument indicates the full module name (including the package name, if this is a submodule of a package). The file argument is an open file, and pathname is the corresponding file name; these can be
'', respectively, when the module is a package or not being loaded from a file. The description argument is a tuple, as would be returned by
get_suffixes(), describing what kind of module must be loaded.
If the load is successful, the return value is the module object; otherwise, an exception (usually
ImportError) is raised.
Return a new empty module object called name. This object is not inserted in
Trueif the import lock is currently held, else
False. On platforms without threads, always return
On platforms with threads, a thread executing an import holds an internal lock until the import is complete. This lock blocks other threads from doing an import until the original import completes, which in turn prevents other threads from seeing incomplete module objects constructed by the original thread while in the process of completing its import (and the imports, if any, triggered by that).
Acquire the interpreter’s import lock for the current thread. This lock should be used by import hooks to ensure thread-safety when importing modules.
Once a thread has acquired the import lock, the same thread may acquire it again without blocking; the thread must release it once for each time it has acquired it.
On platforms without threads, this function does nothing.
New in version 2.3.
Release the interpreter’s import lock. On platforms without threads, this function does nothing.
New in version 2.3.
The following constants with integer values, defined in this module, are used to
indicate the search result of
The module was found as a source file.
The module was found as a compiled code object file.
The module was found as dynamically loadable shared library.
The module was found as a package directory.
The module was found as a built-in module.
Initialize the built-in module called name and return its module object along with storing it in
sys.modules. If the module was already initialized, it will be initialized again. Re-initialization involves the copying of the built-in module’s
__dict__from the cached module over the module’s entry in
sys.modules. If there is no built-in module called name,
Initialize the frozen module called name and return its module object. If the module was already initialized, it will be initialized again. If there is no frozen module called name,
Noneis returned. (Frozen modules are modules written in Python whose compiled byte-code object is incorporated into a custom-built Python interpreter by Python’s freeze utility. See
1if there is a built-in module called name which can be initialized again. Return
-1if there is a built-in module called name which cannot be initialized again (see
0if there is no built-in module called name.
Trueif there is a frozen module (see
init_frozen()) called name, or
Falseif there is no such module.
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 again. The name argument is used to create or access a module object. The pathname argument points to the byte-compiled code file. The 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.
load_dynamic(name, pathname[, 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 again. Re-initialization involves copying the
__dict__attribute of the cached instance of the module over the value used in the module cached in
sys.modules. The pathname argument must point to the shared library. The name argument is used to construct the name of the initialization function: an external C function called
initname()in the shared library is called. The optional file argument is ignored. (Note: using shared libraries is highly system dependent, and not all systems support it.)
CPython implementation detail: The import internals identify extension modules by filename, so doing
foo = load_dynamic("foo", "mod.so")and
bar = load_dynamic("bar", "mod.so")will result in both foo and bar referring to the same module, regardless of whether or not
initbarfunction. On systems which support them, symlinks can be used to import multiple modules from the same shared library, as each reference to the module will use a different file name.
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 again. The name argument is used to create or access a module object. The pathname argument points to the source file. The 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
.pyo) exists, it will be used instead of parsing the given source file.
NullImportertype is a PEP 302 import hook that handles non-directory path strings by failing to find any modules. Calling this type with an existing directory or empty string raises
ImportError. Otherwise, a
NullImporterinstance is returned.
Python adds instances of this type to
sys.path_importer_cachefor any path entries that are not directories and are not handled by any other path hooks on
sys.path_hooks. Instances have only one method:
This method always returns
None, indicating that the requested module could not be found.
New in version 2.5.
The following function emulates what was the standard import statement up to
Python 1.4 (no hierarchical module names). (This implementation wouldn’t work
in that version, since
find_module() has been extended and
load_module() has been added in 1.4.)
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()
A more complete example that implements hierarchical module names and includes a
reload() function can be found in the module
module can be found in
Demo/imputil/ in the Python source distribution.