importlib.metadata
– Accessing package metadata¶
Added in version 3.8.
Zmienione w wersji 3.10: importlib.metadata
is no longer provisional.
Source code: 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 Packages, 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 Core metadata specifications.
Ważne
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 packages_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.
Zobacz także
- 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
.
Skorowidz¶
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:
$ 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:
(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 objects.
You can get the metadata for a distribution:
>>> 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, list its constituent files, and get a list of the distribution’s Distribution requirements.
- exception importlib.metadata.PackageNotFoundError¶
Subclass of
ModuleNotFoundError
raised by several functions in this module when queried for a distribution package which is not installed in the current Python environment.
Functional API¶
This package provides the following functionality via its public API.
Entry points¶
- importlib.metadata.entry_points(**select_params)¶
Returns a
EntryPoints
instance describing entry points for the current environment. Any given keyword parameters are passed to theselect()
method for comparison to the attributes of the individual entry point definitions.Note: it is not currently possible to query for entry points based on their
EntryPoint.dist
attribute (as differentDistribution
instances do not currently compare equal, even if they have the same attributes)
- class importlib.metadata.EntryPoints¶
Details of a collection of installed entry points.
Also provides a
.groups
attribute that reports all identifed entry point groups, and a.names
attribute that reports all identified entry point names.
- class importlib.metadata.EntryPoint¶
Details of an installed entry point.
Each
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()
The entry_points()
function returns a 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.
Zmienione w wersji 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
backports.entry_points_selectable
for compatibility options.
Zmienione w wersji 3.13: EntryPoint
objects no longer present a tuple-like interface
(__getitem__()
).
Distribution metadata¶
- importlib.metadata.metadata(distribution_name)¶
Return the distribution metadata corresponding to the named distribution package as a
PackageMetadata
instance.Raises
PackageNotFoundError
if the named distribution package is not installed in the current Python environment.
- class importlib.metadata.PackageMetadata¶
- A concrete implementation of the
-
In addition to providing the defined protocol methods and attributes, subscripting the instance is equivalent to calling the
get()
method.
Every Distribution Package
includes some metadata, which you can extract using the metadata()
function:
>>> wheel_metadata = metadata('wheel')
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']
'>=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.*'
The full set of available metadata is not described here. See the PyPA Core metadata specification for additional details.
Zmienione w wersji 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.
Distribution versions¶
- importlib.metadata.version(distribution_name)¶
Return the installed distribution package version for the named distribution package.
Raises
PackageNotFoundError
if the named distribution package is not installed in the current Python environment.
The version()
function is the quickest way to get a
Distribution Package’s version
number, as a string:
>>> version('wheel')
'0.32.3'
Distribution files¶
- importlib.metadata.files(distribution_name)¶
Return the full set of files contained within the named distribution package.
Raises
PackageNotFoundError
if the named distribution package is not installed in the current Python environment.Returns
None
if the distribution is found but the installation database records reporting the files associated with the distribuion package are missing.
- class importlib.metadata.PackagePath¶
A
pathlib.PurePath
derived object with additionaldist
,size
, andhash
properties corresponding to the distribution package’s installation metadata for that file.
The files()
function takes a
Distribution Package
name and returns all of the files installed by this distribution. Each file is reported
as a PackagePath
instance. 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 the absolute
path to the file:
>>> util.locate()
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.
Distribution requirements¶
- importlib.metadata.requires(distribution_name)¶
Return the declared dependency specifiers for the named distribution package.
Raises
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,
use the requires()
function:
>>> requires('wheel')
["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]
Mapping import to distribution packages¶
- importlib.metadata.packages_distributions()¶
Return a mapping from the top level module and import package names found via
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 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.
Added in version 3.10.
Distributions¶
- importlib.metadata.distribution(distribution_name)¶
Return a
Distribution
instance describing the named distribution package.Raises
PackageNotFoundError
if the named distribution package is not installed in the current Python environment.
- class importlib.metadata.Distribution¶
Details of an installed distribution package.
Note: different
Distribution
instances do not currently compare equal, even if they relate to the same installed distribution and accordingly have the same attributes.
While the module level API described above is the most common and convenient usage,
you can get all of that information from the Distribution
class.
Distribution
is an abstract object that represents the metadata for
a Python Distribution Package.
You can get the concreate Distribution
subclass instance for an installed
distribution package by calling the distribution()
function:
>>> from importlib.metadata import distribution
>>> dist = distribution('wheel')
>>> type(dist)
<class 'importlib.metadata.PathDistribution'>
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 Distribution
instances:
>>> dist.metadata['Requires-Python']
'>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
>>> dist.metadata['License']
'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 PyPA Core metadata specification for additional details.
Added in version 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 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:
importlib.metadata
does not honorbytes
objects onsys.path
.importlib.metadata
will incidentally honorpathlib.Path
objects onsys.path
even though such values will be ignored for imports.
Extending the search algorithm¶
Because 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 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 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
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.