Doc/library/importlib.metadata.rst
.. _using:
!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 <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>,
such as its entry points
or its top-level names (Import Package <https://packaging.python.org/en/latest/glossary/#term-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 <https://packaging.python.org/en/latest/specifications/core-metadata/#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:packages_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.
.. seealso::
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.
Let's say you wanted to get the version string for a
Distribution Package <https://packaging.python.org/en/latest/glossary/#term-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 <entry-points> objects.
You can get the :ref:metadata for a distribution <metadata>::
>>> 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 <version>, list its
:ref:constituent files <files>, and get a list of the distribution's
:ref:requirements.
.. exception:: PackageNotFoundError
Subclass of :class:ModuleNotFoundError raised by several functions in this
module when queried for a distribution package which is not installed in the
current Python environment.
This package provides the following functionality via its public API.
.. _entry-points:
.. function:: entry_points(**select_params)
Returns a :class:EntryPoints instance describing entry points for the
current environment. Any given keyword parameters are passed to the
:meth:!select method for comparison to the attributes of
the individual entry point definitions.
Note: to query for entry points based on :attr:!EntryPoint.dist attribute,
use :meth:Distribution.entry_points instead (as different :class:Distribution
instances do not currently compare equal, even if they have the same attributes)
.. class:: EntryPoints
Details of a collection of installed entry points.
Also provides a .groups attribute that reports all identified entry
point groups, and a .names attribute that reports all identified entry
point names.
.. class:: EntryPoint
Details of an installed entry point.
Each :class:!EntryPoint instance has .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, and .dist for obtaining
information regarding the distribution package that provides the entry point.
Query all entry points::
>>> eps = entry_points() # doctest: +SKIP
The :func:!entry_points function returns a :class:!EntryPoints object,
a collection of all :class:!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']
:class:!EntryPoints has a :meth:!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 :func:!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
<function main at 0x103528488>
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 <https://setuptools.pypa.io/en/latest/userguide/entry_point.html>_
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:
.. function:: metadata(distribution_name)
Return the distribution metadata corresponding to the named
distribution package as a :class:PackageMetadata instance.
Raises :exc:PackageNotFoundError if the named distribution
package is not installed in the current Python environment.
.. class:: PackageMetadata
A concrete implementation of the
PackageMetadata protocol <https://importlib-metadata.readthedocs.io/en/latest/api.html#importlib_metadata.PackageMetadata>_.
In addition to providing the defined protocol methods and attributes, subscripting
the instance is equivalent to calling the :meth:!get method.
Every Distribution Package <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>_
includes some metadata, which you can extract using the :func:!metadata function::
>>> wheel_metadata = metadata('wheel') # doctest: +SKIP
The keys of the returned data structure 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.*'
:class:PackageMetadata also presents a :attr:!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.*'
The full set of available metadata is not described here.
See the PyPA Core metadata specification <https://packaging.python.org/en/latest/specifications/core-metadata/#core-metadata>_ for additional details.
.. 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:
.. function:: version(distribution_name)
Return the installed distribution package
version <https://packaging.python.org/en/latest/specifications/core-metadata/#version>__
for the named distribution package.
Raises :exc:PackageNotFoundError if the named distribution
package is not installed in the current Python environment.
The :func:!version function is the quickest way to get a
Distribution Package <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>_'s version
number, as a string::
>>> version('wheel') # doctest: +SKIP
'0.32.3'
.. _files:
.. function:: files(distribution_name)
Return the full set of files contained within the named
distribution package as :class:PackagePath instances.
Raises :exc:PackageNotFoundError if the named distribution
package is not installed in the current Python environment.
Returns :const:None if the distribution is found but the installation
database records reporting the files associated with the distribution package
are missing.
.. class:: PackagePath
A :class:`pathlib.PurePath` derived object with additional ``dist``,
``size``, and ``hash`` properties corresponding to the distribution
package's installation metadata for that file, also:
.. method:: locate()
If possible, return the concrete :class:`SimplePath` allowing to access data,
or raise a :exc:`NotImplementedError` otherwise.
.. class:: SimplePath
A protocol representing a minimal subset of :class:`pathlib.Path` that allows to
check if it ``exists()``, to traverse using ``joinpath()`` and ``parent``,
and to retrieve data using ``read_text()`` and ``read_bytes()``.
The :func:!files function takes a
Distribution Package <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>_
name and returns all of the files installed by this distribution. 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
<importlib.metadata._hooks.PathDistribution object at 0x101e0cef0>
>>> util.hash # doctest: +SKIP
<FileHash mode: sha256 value: bYkw5oMccfazVCoYQwKkkemoVyMAFoR34mmKBx8R1NI>
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 :meth:!locate method to get 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, :func:!files will
return :const:None. The caller may wish to wrap calls to
:func:!files in always_iterable <https://more-itertools.readthedocs.io/en/stable/api.html#more_itertools.always_iterable>_
or otherwise guard against this condition if the target
distribution is not known to have the metadata present.
.. _requirements:
.. function:: requires(distribution_name)
Return the declared dependency specifiers for the named distribution package.
Raises :exc:PackageNotFoundError if the named distribution
package is not installed in the current Python environment.
To get the full set of requirements for a Distribution Package <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>_,
use the :func:!requires
function::
>>> requires('wheel') # doctest: +SKIP
["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]
.. _package-distributions: .. _import-distribution-package-mapping:
.. function:: packages_distributions()
Return a mapping from the top level module and import package
names found via :data:sys.meta_path to the names of the distribution
packages (if any) that provide the corresponding files.
To allow for namespace packages (which may have members provided by multiple distribution packages), each top level import name maps to a list of distribution names rather than mapping directly to a single name.
A convenience method to resolve the Distribution Package <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>_
name (or names, in the case of a namespace package)
that provide each importable top-level
Python module or Import Package <https://packaging.python.org/en/latest/glossary/#term-Import-Package>_::
>>> packages_distributions()
{'importlib_metadata': ['importlib-metadata'], 'yaml': ['PyYAML'], 'jaraco': ['jaraco.classes', 'jaraco.functools'], ...}
Some editable installs, do not supply top-level names <https://github.com/pypa/packaging-problems/issues/609>_, and thus this
function is not reliable with such installs.
.. versionadded:: 3.10
.. _distributions:
While the module level API described above is the most common and convenient usage,
all that information is accessible from the :class:Distribution class.
:class:!Distribution is an abstract object that represents the metadata for
a Python Distribution Package <https://packaging.python.org/en/latest/glossary/#term-Distribution-Package>_.
Get the concrete :class:!Distribution subclass instance for an installed
distribution package by calling the :func:distribution function::
>>> from importlib.metadata import distribution # doctest: +SKIP
>>> dist = distribution('wheel') # doctest: +SKIP
>>> type(dist) # doctest: +SKIP
<class 'importlib.metadata.PathDistribution'>
.. function:: distribution(distribution_name)
Return a :class:Distribution instance describing the named
distribution package.
Raises :exc:PackageNotFoundError if the named distribution
package is not installed in the current Python environment.
Thus, an alternative way to get e.g. the version number is through the
:attr:Distribution.version attribute::
>>> dist.version # doctest: +SKIP
'0.32.3'
The same applies for :func:entry_points and :func:files.
.. class:: Distribution
Details of an installed distribution package.
Note: different :class:!Distribution instances do not currently compare
equal, even if they relate to the same installed distribution and
accordingly have the same attributes.
.. staticmethod:: at(path) .. classmethod:: from_name(name)
Return a :class:`!Distribution` instance at the given path or
with the given name.
.. classmethod:: discover(*, context=None, **kwargs)
Returns an iterable of :class:`!Distribution` instances for all packages
(see distribution-discovery_).
The optional argument *context* is a :class:`DistributionFinder.Context`
instance, used to modify the search for distributions. Alternatively,
*kwargs* may contain keyword arguments for constructing a new
:class:`!DistributionFinder.Context`.
.. attribute:: metadata :type: PackageMetadata
There are all kinds of additional metadata available on :class:`!Distribution`
instances as a :class:`PackageMetadata` instance::
>>> dist.metadata['Requires-Python'] # doctest: +SKIP
'>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
>>> dist.metadata['License'] # doctest: +SKIP
'MIT'
The full set of available metadata is not described here.
See the PyPA `Core metadata specification <https://packaging.python.org/en/latest/specifications/core-metadata/#core-metadata>`_ for additional details.
.. attribute:: name :type: str .. attribute:: requires :type: list[str] .. attribute:: version :type: str
A few metadata fields are also available as shortcut properties.
.. versionadded:: 3.10
The ``name`` shortcut was added.
.. attribute:: origin
For editable packages, an ``origin`` property may present :pep:`610`
metadata (for non-editable packages, ``origin`` is :const:`None`)::
>>> dist.origin.url
'file:///path/to/wheel-0.32.3.editable-py3-none-any.whl'
The ``origin`` object follows the `Direct URL Data Structure
<https://packaging.python.org/en/latest/specifications/direct-url-data-structure/>`_.
.. versionadded:: 3.13
.. attribute:: entry_points :type: EntryPoints
The entry points provided by this distribution package.
.. attribute:: files :type: list[PackagePath] | None
All files contained in this distribution package.
Like :func:`files`, this returns :const:`None` if there are no records.
The following two abstract methods need to be implemented when implementing-custom-providers_:
.. method:: locate_file(path)
Like :meth:`!PackagePath.locate`, return a :class:`SimplePath` for the given path.
Takes a :class:`os.PathLike` or a :class:`str`.
.. method:: read_text(filename)
A shortcut for ``distribution.locate_file(filename).read_text()``.
.. _distribution-discovery:
By default, this package provides built-in support for discovery of metadata
for file system and zip file Distribution Package <https://packaging.python.org/en/latest/glossary/#term-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... class:: DistributionFinder
A :class:~importlib.abc.MetaPathFinder subclass capable of discovering
installed distributions.
Custom providers should implement this interface in order to supply metadata.
.. class:: Context(**kwargs)
A :class:`!Context` gives a custom provider a means to
solicit additional details from the callers of distribution discovery
functions like :func:`distributions` or :meth:`Distribution.discover`
beyond :attr:`!.name` and :attr:`!.path` when searching
for distributions.
For example, a provider could expose suites of packages in either a
"public" or "private" ``realm``. A caller of distribution discovery
functions may wish to query only for distributions in a particular realm
and could call ``distributions(realm="private")`` to signal to the
custom provider to only include distributions from that
realm.
Each :class:`!DistributionFinder` must expect any parameters and should
attempt to honor the canonical parameters defined below when
appropriate.
See the section on :ref:`implementing-custom-providers` for more details.
.. attribute:: name
Specific name for which a distribution finder should match.
A :attr:`!.name` of ``None`` matches all distributions.
.. attribute:: path
A property providing the sequence of directory paths that a
distribution finder should search.
Typically refers to Python installed package paths such as
"site-packages" directories and defaults to :attr:`sys.path`.
.. function:: distributions(**kwargs)
Returns an iterable of :class:Distribution instances for all packages.
The kwargs argument may contain either a keyword argument context, a
:class:DistributionFinder.Context instance, or pass keyword arguments for
constructing a new :class:!DistributionFinder.Context. The
:class:!DistributionFinder.Context is used to modify the search for
distributions.
.. _implementing-custom-providers:
importlib.metadata address two API surfaces, one for consumers
and another for providers. Most users are consumers, consuming
metadata provided by the packages. There are other use-cases, however,
where users wish to expose metadata through some other mechanism,
such as alongside a custom importer. Such a use case calls for a
custom provider.
Because Distribution Package <https://packaging.python.org/en/latest/glossary/#term-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 <finders-and-loaders>. 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 implementation has hooks integrated into the PathFinder,
serving metadata for distribution packages found on the file system.
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
:class:DistributionFinder abstract base class, which defines this abstract
method::
@abc.abstractmethod
def find_distributions(context=DistributionFinder.Context()) -> Iterable[Distribution]:
"""Return an iterable of all Distribution instances capable of
loading the metadata for packages for the indicated ``context``.
"""
The :class:DistributionFinder.Context object provides
:attr:~DistributionFinder.Context.path and
:attr:~DistributionFinder.Context.name properties indicating the path to
search and name to match and may supply other relevant context sought by the
consumer.
In practice, to support finding distribution package
metadata in locations other than the file system, subclass
:class:!Distribution and implement the abstract methods. Then from
a custom finder, return instances of this derived :class:!Distribution in the
find_distributions() method.
Imagine 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
:class: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.Distribution):
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 :attr:!Distribution.files) or override the
implementation of :attr:!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