: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 parent directory name .. is not allowed, and nor is a rooted name (starting with a /).

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

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()

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>.