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 (.pyc files). (This value may be different for each Python version.)
Try to find the module name on the search path path. If path is 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 path is omitted or None, the list of directory names given by sys.path is searched, but first it searches a few special places: it 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).
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, ImportError is 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 PKG_DIRECTORY.
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 find_module() and 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 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 None and '', 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 True if the import lock is currently held, else False. On platforms without threads, always return False.
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. On platforms without threads, this function does nothing.
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 find_module().
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.
The NullImporter type 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 NullImporter instance is returned.
Python adds instances of this type to sys.path_importer_cache for 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:
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 knee. The knee module can be found in Demo/imputil/ in the Python source distribution.