importlib_metadata
is a library that provides access to the metadata of an installed packaging:Distribution Package
, such as its entry points or its top-level names (packaging: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 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 pip. Specifically, it works with distributions with discoverable dist-info
or egg-info
directories, and metadata defined by the 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 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 sys.path
. Through an extension mechanism, the metadata can live almost anywhere.
- https://importlib-metadata.readthedocs.io/
The documentation for
importlib_metadata
, which supplies a backport ofimportlib.metadata
. This includes an API reference for this module's classes and functions, as well as a migration guide for existing users ofpkg_resources
.
Let's say you wanted to get the version string for a packaging:Distribution Package
you've installed using pip
. We start by creating a virtual environment and installing something into it:
$ python3 -m venv example
$ source example/bin/activate
(example) $ python -m pip install importlib_metadata
(example) $ python -m pip install wheel
You can get the version string for wheel
by running the following:
(example) $ python
>>> from importlib_metadata import version
>>> version('wheel')
'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 EntryPoint <entry-points>
objects.
You can get the metadata for a distribution <metadata>
:
>>> list(metadata('wheel'))
['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 distribution's version number <version>
, list its constituent files <files>
, and get a list of the distribution's requirements
.
This package provides the following functionality via its public API.
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()
The entry_points()
function returns an EntryPoints
object, a collection of all EntryPoint
objects with names
and groups
attributes for convenience:
>>> sorted(eps.groups)
['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')
Equivalently, since entry_points
passes keyword arguments through to select:
>>> scripts = entry_points(group='console_scripts')
Pick out a specific script named "wheel" (found in the wheel project):
>>> 'wheel' in scripts.names
True
>>> wheel = scripts['wheel']
Equivalently, query for that entry point during selection:
>>> (wheel,) = entry_points(group='console_scripts', name='wheel')
>>> (wheel,) = entry_points().select(group='console_scripts', name='wheel')
Inspect the resolved entry point:
>>> wheel
EntryPoint(name='wheel', value='wheel.cli:main', group='console_scripts')
>>> wheel.module
'wheel.cli'
>>> wheel.attr
'main'
>>> wheel.extras
[]
>>> main = wheel.load()
>>> main
<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 for more information on entry points, their definition, and usage.
Compatibility Note
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 backports.entry_points_selectable for compatibility options.
Every packaging:Distribution Package
includes some metadata, which you can extract using the metadata()
function:
>>> wheel_metadata = metadata('wheel')
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']
'>=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.
The version()
function is the quickest way to get a packaging:Distribution Package
's version number, as a string:
>>> version('wheel')
'0.32.3'
You can also get the full set of files contained within a distribution. The files()
function takes a packaging:Distribution Package
name and returns all of the files installed by this distribution. Each file object returned is a PackagePath
, a 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]
>>> util
PackagePath('wheel/util.py')
>>> util.size
859
>>> util.dist
<importlib_metadata._hooks.PathDistribution object at 0x101e0cef0>
>>> util.hash
<FileHash mode: sha256 value: bYkw5oMccfazVCoYQwKkkemoVyMAFoR34mmKBx8R1NI>
Once you have the file, you can also read its contents:
>>> print(util.read_text())
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.
To get the full set of requirements for a packaging:Distribution Package
, use the requires()
function:
>>> requires('wheel')
["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]
A convenience method to resolve the packaging:Distribution Package
name (or names, in the case of a namespace package) that provide each importable top-level Python module or packaging: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.
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 packaging:Distribution Package
. You can get the Distribution
instance:
>>> from importlib_metadata import distribution
>>> dist = distribution('wheel')
Thus, an alternative way to get the version number is through the Distribution
instance:
>>> dist.version
'0.32.3'
There are all kinds of additional metadata available on the Distribution
instance:
>>> dist.metadata['Requires-Python']
'>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
>>> dist.metadata['License']
'MIT'
The full set of available metadata is not described here. See the packaging:core-metadata
for additional details.
By default, this package provides built-in support for discovery of metadata for file system and zip file 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 honorbytes
objects onsys.path
.importlib_metadata
will incidentally honor :pypathlib.Path
objects onsys.path
even though such values will be ignored for imports.
Because packaging:Distribution Package
metadata is not available through 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 meta path finders <meta path finder>
on 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 :pyimportlib.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 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.