:mod:`pkgutil` --- Package extension utility
============================================

.. module:: pkgutil
   :synopsis: Utilities for the import system.

**Source code:** :source:`Lib/pkgutil.py`

--------------

This module provides utilities for the import system, in particular package
support.

.. class:: ModuleInfo(module_finder, name, ispkg)

    A namedtuple that holds a brief summary of a module's info.

    .. versionadded:: 3.6

.. function:: extend_path(path, name)

   Extend the search path for the modules which comprise a package.  Intended
   use is to place the following code in a package's :file:`__init__.py`::

      from pkgutil import extend_path
      __path__ = extend_path(__path__, __name__)

   This will add to the package's ``__path__`` all subdirectories of directories
   on ``sys.path`` named after the package.  This is useful if one wants to
   distribute different parts of a single logical package as multiple
   directories.

   It also looks for :file:`\*.pkg` files beginning where ``*`` matches the
   *name* argument.  This feature is similar to :file:`\*.pth` files (see the
   :mod:`site` module for more information), except that it doesn't special-case
   lines starting with ``import``.  A :file:`\*.pkg` file is trusted at face
   value: apart from checking for duplicates, all entries found in a
   :file:`\*.pkg` file are added to the path, regardless of whether they exist
   on the filesystem.  (This is a feature.)

   If the input path is not a list (as is the case for frozen packages) it is
   returned unchanged.  The input path is not modified; an extended copy is
   returned.  Items are only appended to the copy at the end.

   It is assumed that :data:`sys.path` is a sequence.  Items of :data:`sys.path`
   that are not strings referring to existing directories are ignored. Unicode
   items on :data:`sys.path` that cause errors when used as filenames may cause
   this function to raise an exception (in line with :func:`os.path.isdir`
   behavior).


.. class:: ImpImporter(dirname=None)

   :pep:`302` Finder that wraps Python's "classic" import algorithm.

   If *dirname* is a string, a :pep:`302` finder is created that searches that
   directory.  If *dirname* is ``None``, a :pep:`302` finder is created that
   searches the current :data:`sys.path`, plus any modules that are frozen or
   built-in.

   Note that :class:`ImpImporter` does not currently support being used by
   placement on :data:`sys.meta_path`.

   .. deprecated:: 3.3
      This emulation is no longer needed, as the standard import mechanism
      is now fully PEP 302 compliant and available in :mod:`importlib`.


.. class:: ImpLoader(fullname, file, filename, etc)

   :term:`Loader` that wraps Python's "classic" import algorithm.

   .. deprecated:: 3.3
      This emulation is no longer needed, as the standard import mechanism
      is now fully PEP 302 compliant and available in :mod:`importlib`.


.. function:: find_loader(fullname)

   Retrieve a module :term:`loader` for the given *fullname*.

   This is a backwards compatibility wrapper around
   :func:`importlib.util.find_spec` that converts most failures to
   :exc:`ImportError` and only returns the loader rather than the full
   :class:`ModuleSpec`.

   .. versionchanged:: 3.3
      Updated to be based directly on :mod:`importlib` rather than relying
      on the package internal PEP 302 import emulation.

   .. versionchanged:: 3.4
      Updated to be based on :pep:`451`

.. function:: get_importer(path_item)

   Retrieve a :term:`finder` for the given *path_item*.

   The returned finder is cached in :data:`sys.path_importer_cache` if it was
   newly created by a path hook.

   The cache (or part of it) can be cleared manually if a rescan of
   :data:`sys.path_hooks` is necessary.

   .. versionchanged:: 3.3
      Updated to be based directly on :mod:`importlib` rather than relying
      on the package internal PEP 302 import emulation.


.. function:: get_loader(module_or_name)

   Get a :term:`loader` object for *module_or_name*.

   If the module or package is accessible via the normal import mechanism, a
   wrapper around the relevant part of that machinery is returned.  Returns
   ``None`` if the module cannot be found or imported.  If the named module is
   not already imported, its containing package (if any) is imported, in order
   to establish the package ``__path__``.

   .. versionchanged:: 3.3
      Updated to be based directly on :mod:`importlib` rather than relying
      on the package internal PEP 302 import emulation.

   .. versionchanged:: 3.4
      Updated to be based on :pep:`451`


.. function:: iter_importers(fullname='')

   Yield :term:`finder` objects for the given module name.

   If fullname contains a '.', the finders will be for the package
   containing fullname, otherwise they will be all registered top level
   finders (i.e. those on both sys.meta_path and sys.path_hooks).

   If the named module is in a package, that package is imported as a side
   effect of invoking this function.

   If no module name is specified, all top level finders are produced.

   .. versionchanged:: 3.3
      Updated to be based directly on :mod:`importlib` rather than relying
      on the package internal PEP 302 import emulation.


.. function:: iter_modules(path=None, prefix='')

   Yields :class:`ModuleInfo` for all submodules on *path*, or, if
   *path* is ``None``, all top-level modules on ``sys.path``.

   *path* should be either ``None`` or a list of paths to look for modules in.

   *prefix* is a string to output on the front of every module name on output.

   .. note::

      Only works for a :term:`finder` which defines an ``iter_modules()``
      method. This interface is non-standard, so the module also provides
      implementations for :class:`importlib.machinery.FileFinder` and
      :class:`zipimport.zipimporter`.

   .. versionchanged:: 3.3
      Updated to be based directly on :mod:`importlib` rather than relying
      on the package internal PEP 302 import emulation.


.. function:: walk_packages(path=None, prefix='', onerror=None)

   Yields :class:`ModuleInfo` for all modules recursively on
   *path*, or, if *path* is ``None``, all accessible modules.

   *path* should be either ``None`` or a list of paths to look for modules in.

   *prefix* is a string to output on the front of every module name on output.

   Note that this function must import all *packages* (*not* all modules!) on
   the given *path*, in order to access the ``__path__`` attribute to find
   submodules.

   *onerror* is a function which gets called with one argument (the name of the
   package which was being imported) if any exception occurs while trying to
   import a package.  If no *onerror* function is supplied, :exc:`ImportError`\s
   are caught and ignored, while all other exceptions are propagated,
   terminating the search.

   Examples::

      # list all modules python can access
      walk_packages()

      # list all submodules of ctypes
      walk_packages(ctypes.__path__, ctypes.__name__ + '.')

   .. note::

      Only works for a :term:`finder` which defines an ``iter_modules()``
      method. This interface is non-standard, so the module also provides
      implementations for :class:`importlib.machinery.FileFinder` and
      :class:`zipimport.zipimporter`.

   .. versionchanged:: 3.3
      Updated to be based directly on :mod:`importlib` rather than relying
      on the package internal PEP 302 import emulation.


.. function:: get_data(package, resource)

   Get a resource from a package.

   This is a wrapper for the :term:`loader`
   :meth:`get_data <importlib.abc.ResourceLoader.get_data>` API.  The
   *package* argument should be the name of a package, in standard module format
   (``foo.bar``).  The *resource* argument should be in the form of a relative
   filename, using ``/`` as the path separator.

   The function returns a binary string that is the contents of the specified
   resource.

   This function uses the :term:`loader` method
   :func:`~importlib.abc.FileLoader.get_data`
   to support modules installed in the filesystem, but also in zip files,
   databases, or elsewhere.

   For packages located in the filesystem, which have already been imported,
   this is the rough equivalent of::

      d = os.path.dirname(sys.modules[package].__file__)
      data = open(os.path.join(d, resource), 'rb').read()

   Like the :func:`open` function, :func:`!get_data` can follow parent
   directories (``../``) and absolute paths (starting with ``/`` or ``C:/``,
   for example).

   .. warning::

      This function is intended for trusted input.
      It does not verify that *resource* "belongs" to *package*.

   If you use a user-provided *resource* path, consider verifying it.
   For example, require an alphanumeric filename with a known extension, or
   install and check a list of known resources.

   If the package cannot be located or loaded, or it uses a :term:`loader`
   which does not support :meth:`get_data <importlib.abc.ResourceLoader.get_data>`,
   then ``None`` is returned.  In particular, the :term:`loader` for
   :term:`namespace packages <namespace package>` does not support
   :meth:`get_data <importlib.abc.ResourceLoader.get_data>`.

   .. seealso::

      The :mod:`importlib.resources` module provides structured access to
      module resources.

