: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__)

For each directory on :data:sys.path that has a subdirectory that matches the package name, add the subdirectory to the package's :attr:~module.__path__. 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 skipping blank lines and ignoring comments, 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).

.. 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:: 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 :data:sys.meta_path and :data: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 :data: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). It can open compilation/installation artifacts like .py and .pyc files or files with :func:reserved filenames <os.path.isreserved>. To be compatible with non-filesystem loaders, avoid using these features.

.. 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.

.. function:: resolve_name(name)

Resolve a name to an object.

This functionality is used in numerous places in the standard library (see :issue:12915) - and equivalent functionality is also in widely used third-party packages such as setuptools, Django and Pyramid.

It is expected that name will be a string in one of the following formats, where W is shorthand for a valid Python identifier and dot stands for a literal period in these pseudo-regexes:

• W(.W)*
• W(.W)*:(W(.W)*)?

The first form is intended for backward compatibility only. It assumes that some part of the dotted name is a package, and the rest is an object somewhere within that package, possibly nested inside other objects. Because the place where the package stops and the object hierarchy starts can't be inferred by inspection, repeated attempts to import must be done with this form.

In the second form, the caller makes the division point clear through the provision of a single colon: the dotted name to the left of the colon is a package to be imported, and the dotted name to the right is the object hierarchy within that package. Only one import is needed in this form. If it ends with the colon, then a module object is returned.

The function will return an object (which might be a module), or raise one of the following exceptions:

:exc:ValueError -- if name isn't in a recognised format.

:exc:ImportError -- if an import failed when it shouldn't have.

:exc:AttributeError -- If a failure occurred when traversing the object hierarchy within the imported package to get to the desired object.

.. versionadded:: 3.9