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gh-97781: Apply changes from importlib_metadata 5. #97785

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Oct 6, 2022
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gh-97781: Apply changes from importlib_metadata 5. #97785

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49b5db9
gh-97781: Apply changes from importlib_metadata 5.
jaraco Oct 3, 2022
5df1c55
Apply changes from upstream
jaraco Oct 5, 2022
1692bf4
Apply changes from upstream.
jaraco Oct 6, 2022
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gh-97781: Apply changes from importlib_metadata 5.
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@jaraco
jaraco committed Oct 3, 2022
commit 49b5db96c3b8a3c77104e9395198619ada220ea0
106 changes: 72 additions & 34 deletions 106 Doc/library/importlib.metadata.rst
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Expand Up @@ -13,21 +13,39 @@

**Source code:** :source:`Lib/importlib/metadata/__init__.py`

``importlib.metadata`` is a library that provides access to installed
package metadata, such as its entry points or its
top-level name. Built in part on Python's import system, this library
``importlib_metadata`` is a library that provides access to
the metadata of an installed :term:`packaging:Distribution Package`,
such as its entry points
or its top-level names (:term:`packaging:Import Package`s, modules, if any).
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Built in part on Python's import system, this library
intends to replace similar functionality in the `entry point
API`_ and `metadata API`_ of ``pkg_resources``. Along with
:mod:`importlib.resources`,
this package can eliminate the need to use the older and less efficient
``pkg_resources`` package.

By "installed package" we generally mean a third-party package installed into
Python's ``site-packages`` directory via tools such as `pip
<https://pypi.org/project/pip/>`_. Specifically,
it means a package with either a discoverable ``dist-info`` or ``egg-info``
directory, and metadata defined by :pep:`566` or its older specifications.
By default, package metadata can live on the file system or in zip archives on
``importlib_metadata`` operates on third-party *distribution packages*
installed into Python's ``site-packages`` directory via tools such as
`pip <https://pypi.org/project/pip/>`_.
Specifically, it works with distributions with discoverable
``dist-info`` or ``egg-info`` directories,
and metadata defined by the :ref:`packaging:core-metadata`.

.. important::

These are *not* necessarily equivalent to or correspond 1:1 with
the top-level *import package* names
that can be imported inside Python code.
One *distribution package* can contain multiple *import packages*
(and single modules),
and one top-level *import package*
may map to multiple *distribution packages*
if it is a namespace package.
You can use :ref:`package_distributions() <package-distributions>`
to get a mapping between them.

By default, distribution metadata can live on the file system
or in zip archives on
:data:`sys.path`. Through an extension mechanism, the metadata can live almost
anywhere.

Expand All @@ -37,12 +55,19 @@ anywhere.
https://importlib-metadata.readthedocs.io/
The documentation for ``importlib_metadata``, which supplies a
backport of ``importlib.metadata``.
This includes an `API reference
<https://importlib-metadata.readthedocs.io/en/latest/api.html>`__
for this module's classes and functions,
as well as a `migration guide
<https://importlib-metadata.readthedocs.io/en/latest/migration.html>`__
for existing users of ``pkg_resources``.


Overview
========

Let's say you wanted to get the version string for a package you've installed
Let's say you wanted to get the version string for a
:term:`packaging:Distribution Package` you've installed
using ``pip``. We start by creating a virtual environment and installing
something into it:

Expand Down Expand Up @@ -151,19 +176,19 @@ for more information on entry points, their definition, and usage.
The "selectable" entry points were introduced in ``importlib_metadata``
3.6 and Python 3.10. Prior to those changes, ``entry_points`` accepted
no parameters and always returned a dictionary of entry points, keyed
by group. For compatibility, if no parameters are passed to entry_points,
a ``SelectableGroups`` object is returned, implementing that dict
interface. In the future, calling ``entry_points`` with no parameters
will return an ``EntryPoints`` object. Users should rely on the selection
interface to retrieve entry points by group.
by group. With ``importlib_metadata`` 5.0 and Python 3.12,
``entry_points`` always returns an ``EntryPoints`` object. See
`backports.entry_points_selectable <https://pypi.org/project/backports.entry_points_selectable>`_
for compatibility options.


.. _metadata:

Distribution metadata
---------------------

Every distribution includes some metadata, which you can extract using the
Every :term:`packaging:Distribution Package` includes some metadata,
which you can extract using the
``metadata()`` function::

>>> wheel_metadata = metadata('wheel') # doctest: +SKIP
Expand Down Expand Up @@ -201,7 +226,8 @@ all the metadata in a JSON-compatible form per :PEP:`566`::
Distribution versions
---------------------

The ``version()`` function is the quickest way to get a distribution's version
The ``version()`` function is the quickest way to get a
:term:`packaging:Distribution Package`'s version
number, as a string::

>>> version('wheel') # doctest: +SKIP
Expand All @@ -214,7 +240,8 @@ Distribution files
------------------

You can also get the full set of files contained within a distribution. The
``files()`` function takes a distribution package name and returns all of the
``files()`` function takes a :term:`packaging:Distribution Package` name
and returns all of the
files installed by this distribution. Each file object returned is a
``PackagePath``, a :class:`pathlib.PurePath` derived object with additional ``dist``,
``size``, and ``hash`` properties as indicated by the metadata. For example::
Expand Down Expand Up @@ -259,19 +286,24 @@ distribution is not known to have the metadata present.
Distribution requirements
-------------------------

To get the full set of requirements for a distribution, use the ``requires()``
To get the full set of requirements for a :term:`packaging:Distribution Package`,
use the ``requires()``
function::

>>> requires('wheel') # doctest: +SKIP
["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]


Package distributions
---------------------
.. _package-distributions:
.. _import-distribution-package-mapping:

Mapping import to distribution packages
---------------------------------------

A convenience method to resolve the distribution or
distributions (in the case of a namespace package) for top-level
Python packages or modules::
A convenience method to resolve the :term:`packaging:Distribution Package`
name (or names, in the case of a namespace package)
that provide each importable top-level
Python module or :term:`packaging:Import Package`::

>>> packages_distributions()
{'importlib_metadata': ['importlib-metadata'], 'yaml': ['PyYAML'], 'jaraco': ['jaraco.classes', 'jaraco.functools'], ...}
Expand All @@ -285,7 +317,8 @@ Distributions

While the above API is the most common and convenient usage, you can get all
of that information from the ``Distribution`` class. A ``Distribution`` is an
abstract object that represents the metadata for a Python package. You can
abstract object that represents the metadata for
a Python :term:`packaging:Distribution Package`. You can
get the ``Distribution`` instance::

>>> from importlib.metadata import distribution # doctest: +SKIP
Expand All @@ -305,14 +338,16 @@ instance::
>>> dist.metadata['License'] # doctest: +SKIP
'MIT'

The full set of available metadata is not described here. See :pep:`566`
for additional details.
The full set of available metadata is not described here.
See the :ref:`packaging:core-metadata` for additional details.


Distribution Discovery
======================

By default, this package provides built-in support for discovery of metadata for file system and zip file packages. This metadata finder search defaults to ``sys.path``, but varies slightly in how it interprets those values from how other import machinery does. In particular:
By default, this package provides built-in support for discovery of metadata
for file system and zip file :term:`packaging:Distribution Package`\s.
This metadata finder search defaults to ``sys.path``, but varies slightly in how it interprets those values from how other import machinery does. In particular:

- ``importlib.metadata`` does not honor :class:`bytes` objects on ``sys.path``.
- ``importlib.metadata`` will incidentally honor :py:class:`pathlib.Path` objects on ``sys.path`` even though such values will be ignored for imports.
Expand All @@ -321,15 +356,18 @@ By default, this package provides built-in support for discovery of metadata for
Extending the search algorithm
==============================

Because package metadata is not available through :data:`sys.path` searches, or
package loaders directly, the metadata for a package is found through import
system :ref:`finders <finders-and-loaders>`. To find a distribution package's metadata,
Because :term:`packaging:Distribution Package` metadata
is not available through :data:`sys.path` searches, or
package loaders directly,
the metadata for a distribution is found through import
system `finders`_. To find a distribution package's metadata,
``importlib.metadata`` queries the list of :term:`meta path finders <meta path finder>` on
:data:`sys.meta_path`.

The default ``PathFinder`` for Python includes a hook that calls into
``importlib.metadata.MetadataPathFinder`` for finding distributions
loaded from typical file-system-based paths.
By default ``importlib_metadata`` installs a finder for distribution packages
found on the file system.
This finder doesn't actually find any *distributions*,
but it can find their metadata.

The abstract class :py:class:`importlib.abc.MetaPathFinder` defines the
interface expected of finders by Python's import system.
Expand Down
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