.. _using: ======================================================== :mod:`!importlib.metadata` -- Accessing package metadata ======================================================== .. module:: importlib.metadata :synopsis: Accessing package metadata .. versionadded:: 3.8 .. versionchanged:: 3.10 ``importlib.metadata`` is no longer provisional. **Source code:** :source:`Lib/importlib/metadata/__init__.py` ``importlib.metadata`` is a library that provides access to the metadata of an installed `Distribution Package `_, such as its entry points or its top-level names (`Import Package `_\s, modules, if any). 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. ``importlib.metadata`` operates on third-party *distribution packages* installed into Python's ``site-packages`` directory via tools such as :pypi:`pip`. Specifically, it works with distributions with discoverable ``dist-info`` or ``egg-info`` directories, and metadata defined by the `Core metadata specifications `_. .. 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:`packages_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. .. seealso:: https://importlib-metadata.readthedocs.io/ The documentation for ``importlib_metadata``, which supplies a backport of ``importlib.metadata``. This includes an `API reference `__ for this module's classes and functions, as well as a `migration guide `__ for existing users of ``pkg_resources``. Overview ======== Let's say you wanted to get the version string for a `Distribution Package `_ you've installed using ``pip``. We start by creating a virtual environment and installing something into it: .. code-block:: shell-session $ python -m venv example $ source example/bin/activate (example) $ python -m pip install wheel You can get the version string for ``wheel`` by running the following: .. code-block:: pycon (example) $ python >>> from importlib.metadata import version # doctest: +SKIP >>> version('wheel') # doctest: +SKIP '0.32.3' You can also get a collection of entry points selectable by properties of the EntryPoint (typically 'group' or 'name'), such as ``console_scripts``, ``distutils.commands`` and others. Each group contains a collection of :ref:`EntryPoint ` objects. You can get the :ref:`metadata for a distribution `:: >>> list(metadata('wheel')) # doctest: +SKIP ['Metadata-Version', 'Name', 'Version', 'Summary', 'Home-page', 'Author', 'Author-email', 'Maintainer', 'Maintainer-email', 'License', 'Project-URL', 'Project-URL', 'Project-URL', 'Keywords', 'Platform', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Requires-Python', 'Provides-Extra', 'Requires-Dist', 'Requires-Dist'] You can also get a :ref:`distribution's version number `, list its :ref:`constituent files `, and get a list of the distribution's :ref:`requirements`. Functional API ============== This package provides the following functionality via its public API. .. _entry-points: Entry points ------------ The ``entry_points()`` function returns a collection of entry points. Entry points are represented by ``EntryPoint`` instances; each ``EntryPoint`` has a ``.name``, ``.group``, and ``.value`` attributes and a ``.load()`` method to resolve the value. There are also ``.module``, ``.attr``, and ``.extras`` attributes for getting the components of the ``.value`` attribute. Query all entry points:: >>> eps = entry_points() # doctest: +SKIP The ``entry_points()`` function returns an ``EntryPoints`` object, a collection of all ``EntryPoint`` objects with ``names`` and ``groups`` attributes for convenience:: >>> sorted(eps.groups) # doctest: +SKIP ['console_scripts', 'distutils.commands', 'distutils.setup_keywords', 'egg_info.writers', 'setuptools.installation'] ``EntryPoints`` has a ``select`` method to select entry points matching specific properties. Select entry points in the ``console_scripts`` group:: >>> scripts = eps.select(group='console_scripts') # doctest: +SKIP Equivalently, since ``entry_points`` passes keyword arguments through to select:: >>> scripts = entry_points(group='console_scripts') # doctest: +SKIP Pick out a specific script named "wheel" (found in the wheel project):: >>> 'wheel' in scripts.names # doctest: +SKIP True >>> wheel = scripts['wheel'] # doctest: +SKIP Equivalently, query for that entry point during selection:: >>> (wheel,) = entry_points(group='console_scripts', name='wheel') # doctest: +SKIP >>> (wheel,) = entry_points().select(group='console_scripts', name='wheel') # doctest: +SKIP Inspect the resolved entry point:: >>> wheel # doctest: +SKIP EntryPoint(name='wheel', value='wheel.cli:main', group='console_scripts') >>> wheel.module # doctest: +SKIP 'wheel.cli' >>> wheel.attr # doctest: +SKIP 'main' >>> wheel.extras # doctest: +SKIP [] >>> main = wheel.load() # doctest: +SKIP >>> main # doctest: +SKIP The ``group`` and ``name`` are arbitrary values defined by the package author and usually a client will wish to resolve all entry points for a particular group. Read `the setuptools docs `_ for more information on entry points, their definition, and usage. .. versionchanged:: 3.12 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. With ``importlib_metadata`` 5.0 and Python 3.12, ``entry_points`` always returns an ``EntryPoints`` object. See :pypi:`backports.entry_points_selectable` for compatibility options. .. versionchanged:: 3.13 ``EntryPoint`` objects no longer present a tuple-like interface (:meth:`~object.__getitem__`). .. _metadata: Distribution metadata --------------------- Every `Distribution Package `_ includes some metadata, which you can extract using the ``metadata()`` function:: >>> wheel_metadata = metadata('wheel') # doctest: +SKIP The keys of the returned data structure, a ``PackageMetadata``, name the metadata keywords, and the values are returned unparsed from the distribution metadata:: >>> wheel_metadata['Requires-Python'] # doctest: +SKIP '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*' ``PackageMetadata`` also presents a ``json`` attribute that returns all the metadata in a JSON-compatible form per :PEP:`566`:: >>> wheel_metadata.json['requires_python'] '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*' .. note:: The actual type of the object returned by ``metadata()`` is an implementation detail and should be accessed only through the interface described by the `PackageMetadata protocol `_. .. versionchanged:: 3.10 The ``Description`` is now included in the metadata when presented through the payload. Line continuation characters have been removed. The ``json`` attribute was added. .. _version: Distribution versions --------------------- The ``version()`` function is the quickest way to get a `Distribution Package `_'s version number, as a string:: >>> version('wheel') # doctest: +SKIP '0.32.3' .. _files: 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 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:: >>> util = [p for p in files('wheel') if 'util.py' in str(p)][0] # doctest: +SKIP >>> util # doctest: +SKIP PackagePath('wheel/util.py') >>> util.size # doctest: +SKIP 859 >>> util.dist # doctest: +SKIP >>> util.hash # doctest: +SKIP Once you have the file, you can also read its contents:: >>> print(util.read_text()) # doctest: +SKIP import base64 import sys ... def as_bytes(s): if isinstance(s, text_type): return s.encode('utf-8') return s You can also use the ``locate`` method to get a the absolute path to the file:: >>> util.locate() # doctest: +SKIP PosixPath('/home/gustav/example/lib/site-packages/wheel/util.py') In the case where the metadata file listing files (RECORD or SOURCES.txt) is missing, ``files()`` will return ``None``. The caller may wish to wrap calls to ``files()`` in `always_iterable `_ or otherwise guard against this condition if the target distribution is not known to have the metadata present. .. _requirements: Distribution requirements ------------------------- To get the full set of requirements for a `Distribution Package `_, use the ``requires()`` function:: >>> requires('wheel') # doctest: +SKIP ["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"] .. _package-distributions: .. _import-distribution-package-mapping: Mapping import to distribution packages --------------------------------------- A convenience method to resolve the `Distribution Package `_ name (or names, in the case of a namespace package) that provide each importable top-level Python module or `Import Package `_:: >>> packages_distributions() {'importlib_metadata': ['importlib-metadata'], 'yaml': ['PyYAML'], 'jaraco': ['jaraco.classes', 'jaraco.functools'], ...} Some editable installs, `do not supply top-level names `_, and thus this function is not reliable with such installs. .. versionadded:: 3.10 .. _distributions: 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 `Distribution Package `_. You can get the ``Distribution`` instance:: >>> from importlib.metadata import distribution # doctest: +SKIP >>> dist = distribution('wheel') # doctest: +SKIP Thus, an alternative way to get the version number is through the ``Distribution`` instance:: >>> dist.version # doctest: +SKIP '0.32.3' There are all kinds of additional metadata available on the ``Distribution`` instance:: >>> dist.metadata['Requires-Python'] # doctest: +SKIP '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*' >>> dist.metadata['License'] # doctest: +SKIP 'MIT' For editable packages, an ``origin`` property may present :pep:`610` metadata:: >>> dist.origin.url 'file:///path/to/wheel-0.32.3.editable-py3-none-any.whl' The full set of available metadata is not described here. See the `Core metadata specifications `_ for additional details. .. versionadded:: 3.13 The ``.origin`` property was added. Distribution Discovery ====================== By default, this package provides built-in support for discovery of metadata for file system and zip file `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. Extending the search algorithm ============================== Because `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 :ref:`finders `. To find a distribution package's metadata, ``importlib.metadata`` queries the list of :term:`meta path finders ` on :data:`sys.meta_path`. 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. ``importlib.metadata`` extends this protocol by looking for an optional ``find_distributions`` callable on the finders from :data:`sys.meta_path` and presents this extended interface as the ``DistributionFinder`` abstract base class, which defines this abstract method:: @abc.abstractmethod def find_distributions(context=DistributionFinder.Context()): """Return an iterable of all Distribution instances capable of loading the metadata for packages for the indicated ``context``. """ The ``DistributionFinder.Context`` object provides ``.path`` and ``.name`` properties indicating the path to search and name to match and may supply other relevant context. What this means in practice is that to support finding distribution package metadata in locations other than the file system, subclass ``Distribution`` and implement the abstract methods. Then from a custom finder, return instances of this derived ``Distribution`` in the ``find_distributions()`` method. Example ------- Consider for example a custom finder that loads Python modules from a database:: class DatabaseImporter(importlib.abc.MetaPathFinder): def __init__(self, db): self.db = db def find_spec(self, fullname, target=None) -> ModuleSpec: return self.db.spec_from_name(fullname) sys.meta_path.append(DatabaseImporter(connect_db(...))) That importer now presumably provides importable modules from a database, but it provides no metadata or entry points. For this custom importer to provide metadata, it would also need to implement ``DistributionFinder``:: from importlib.metadata import DistributionFinder class DatabaseImporter(DistributionFinder): ... def find_distributions(self, context=DistributionFinder.Context()): query = dict(name=context.name) if context.name else {} for dist_record in self.db.query_distributions(query): yield DatabaseDistribution(dist_record) In this way, ``query_distributions`` would return records for each distribution served by the database matching the query. For example, if ``requests-1.0`` is in the database, ``find_distributions`` would yield a ``DatabaseDistribution`` for ``Context(name='requests')`` or ``Context(name=None)``. For the sake of simplicity, this example ignores ``context.path``\. The ``path`` attribute defaults to ``sys.path`` and is the set of import paths to be considered in the search. A ``DatabaseImporter`` could potentially function without any concern for a search path. Assuming the importer does no partitioning, the "path" would be irrelevant. In order to illustrate the purpose of ``path``, the example would need to illustrate a more complex ``DatabaseImporter`` whose behavior varied depending on ``sys.path``/``PYTHONPATH``. In that case, the ``find_distributions`` should honor the ``context.path`` and only yield ``Distribution``\ s pertinent to that path. ``DatabaseDistribution``, then, would look something like:: class DatabaseDistribution(importlib.metadata.Distributon): def __init__(self, record): self.record = record def read_text(self, filename): """ Read a file like "METADATA" for the current distribution. """ if filename == "METADATA": return f"""Name: {self.record.name} Version: {self.record.version} """ if filename == "entry_points.txt": return "\n".join( f"""[{ep.group}]\n{ep.name}={ep.value}""" for ep in self.record.entry_points) def locate_file(self, path): raise RuntimeError("This distribution has no file system") This basic implementation should provide metadata and entry points for packages served by the ``DatabaseImporter``, assuming that the ``record`` supplies suitable ``.name``, ``.version``, and ``.entry_points`` attributes. The ``DatabaseDistribution`` may also provide other metadata files, like ``RECORD`` (required for ``Distribution.files``) or override the implementation of ``Distribution.files``. See the source for more inspiration. .. _`entry point API`: https://setuptools.readthedocs.io/en/latest/pkg_resources.html#entry-points .. _`metadata API`: https://setuptools.readthedocs.io/en/latest/pkg_resources.html#metadata-api