.. module:: imp :synopsis: Access the implementation of the import statement. :deprecated:
Source code: :source:`Lib/imp.py`
.. deprecated:: 3.4 The :mod:`imp` package is pending deprecation in favor of :mod:`importlib`.
.. index:: statement: import
This module provides an interface to the mechanisms used to implement the :keyword:`import` statement. It defines the following constants and functions:
.. function:: get_magic() .. index:: pair: file; byte-code Return the magic string value used to recognize byte-compiled code files (:file:`.pyc` files). (This value may be different for each Python version.) .. deprecated:: 3.4 Use :attr:`importlib.util.MAGIC_NUMBER` instead.
.. function:: get_suffixes() 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 :func:`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 :const:`PY_SOURCE`, :const:`PY_COMPILED`, or :const:`C_EXTENSION`, described below. .. deprecated:: 3.3 Use the constants defined on :mod:`importlib.machinery` instead.
.. function:: find_module(name[, path]) Try to find the module *name*. If *path* is omitted or ``None``, the list of directory names given by ``sys.path`` is searched, but first a few special places are searched: the function tries to find a built-in module with the given name (:const:`C_BUILTIN`), then a frozen module (:const:`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 :func:`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 :term:`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 :func:`get_suffixes` describing the kind of module found. If the module is built-in or frozen then *file* and *pathname* are both ``None`` 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, :exc:`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 :const:`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 :func:`find_module` and :func:`load_module` to find and load package *P*, and then use :func:`find_module` with the *path* argument set to ``P.__path__``. When *P* itself has a dotted name, apply this recipe recursively. .. deprecated:: 3.3 Use :func:`importlib.util.find_spec` instead unless Python 3.3 compatibility is required, in which case use :func:`importlib.find_loader`. For example usage of the former case, see the :ref:`importlib-examples` section of the :mod:`importlib` documentation.
.. function:: load_module(name, file, pathname, description) Load a module that was previously found by :func:`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 will reload the module! 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 :func:`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 :exc:`ImportError`) is raised. **Important:** the caller is responsible for closing the *file* argument, if it was not ``None``, even when an exception is raised. This is best done using a :keyword:`try` ... :keyword:`finally` statement. .. deprecated:: 3.3 If previously used in conjunction with :func:`imp.find_module` then consider using :func:`importlib.import_module`, otherwise use the loader returned by the replacement you chose for :func:`imp.find_module`. If you called :func:`imp.load_module` and related functions directly with file path arguments then use a combination of :func:`importlib.util.spec_from_file_location` and :func:`importlib.util.module_from_spec`. See the :ref:`importlib-examples` section of the :mod:`importlib` documentation for details of the various approaches.
.. function:: new_module(name) Return a new empty module object called *name*. This object is *not* inserted in ``sys.modules``. .. deprecated:: 3.4 Use :func:`importlib.util.module_from_spec` instead.
.. function:: reload(module)
Reload a previously imported *module*. The argument must be a module object, so
it must have been successfully imported before. This is useful if you have
edited the module source file using an external editor and want to try out the
new version without leaving the Python interpreter. The return value is the
module object (the same as the *module* argument).
When ``reload(module)`` is executed:
* Python modules' code is recompiled and the module-level code reexecuted,
defining a new set of objects which are bound to names in the module's
dictionary. The ``init`` function of extension modules is not called a second
time.
* As with all other objects in Python the old objects are only reclaimed after
their reference counts drop to zero.
* The names in the module namespace are updated to point to any new or changed
objects.
* Other references to the old objects (such as names external to the module) are
not rebound to refer to the new objects and must be updated in each namespace
where they occur if that is desired.
There are a number of other caveats:
When a module is reloaded, its dictionary (containing the module's global
variables) is retained. Redefinitions of names will override the old
definitions, so this is generally not a problem. If the new version of a module
does not define a name that was defined by the old version, the old definition
remains. This feature can be used to the module's advantage if it maintains a
global table or cache of objects --- with a :keyword:`try` statement it can test
for the table's presence and skip its initialization if desired::
try:
cache
except NameError:
cache = {}
It is legal though generally not very useful to reload built-in or dynamically
loaded modules, except for :mod:`sys`, :mod:`__main__` and :mod:`builtins`.
In many cases, however, extension modules are not designed to be initialized
more than once, and may fail in arbitrary ways when reloaded.
If a module imports objects from another module using :keyword:`from` ...
:keyword:`import` ..., calling :func:`reload` for the other module does not
redefine the objects imported from it --- one way around this is to re-execute
the :keyword:`!from` statement, another is to use :keyword:`!import` and qualified
names (*module*.*name*) instead.
If a module instantiates instances of a class, reloading the module that defines
the class does not affect the method definitions of the instances --- they
continue to use the old class definition. The same is true for derived classes.
.. versionchanged:: 3.3
Relies on both ``__name__`` and ``__loader__`` being defined on the module
being reloaded instead of just ``__name__``.
.. deprecated:: 3.4
Use :func:`importlib.reload` instead.
The following functions are conveniences for handling :func:`find_module`.
.. data:: PY_SOURCE The module was found as a source file. .. deprecated:: 3.3
.. data:: PY_COMPILED The module was found as a compiled code object file. .. deprecated:: 3.3
.. data:: C_EXTENSION The module was found as dynamically loadable shared library. .. deprecated:: 3.3
.. data:: PKG_DIRECTORY The module was found as a package directory. .. deprecated:: 3.3
.. data:: C_BUILTIN The module was found as a built-in module. .. deprecated:: 3.3
.. data:: PY_FROZEN The module was found as a frozen module. .. deprecated:: 3.3
The :class:`NullImporter` type is a :exc:`ImportError`. Otherwise, a :class:`NullImporter` instance is returned.
Instances have only one method:
.. method:: NullImporter.find_module(fullname [, path]) This method always returns ``None``, indicating that the requested module could not be found.
.. versionchanged:: 3.3 ``None`` is inserted into ``sys.path_importer_cache`` instead of an instance of :class:`NullImporter`.
.. deprecated:: 3.4 Insert ``None`` into ``sys.path_importer_cache`` instead.
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 :func:`find_module` has been extended and :func:`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()
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