内容表

  • importlib.metadata – Accessing package metadata
    • 概述
    • 函数式 API
      • 入口点
      • 分发元数据
      • 分发版本
      • 分发文件
      • 分发要求
      • Mapping import to distribution packages
    • 分布
    • Distribution Discovery
    • 扩展搜索算法

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importlib.metadata – Accessing package metadata ¶

Added in version 3.8.

3.10 版改变： importlib.metadata is no longer provisional.

源代码： 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 importlib.resources , this package can eliminate the need to use the older and less efficient pkg_resources 包。

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 .

重要

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() 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.

另请参阅

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 .

概述 ¶

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 对象。

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 分发要求 .

函数式 API ¶

This package provides the following functionality via its public API.

入口点 ¶

The entry_points() function returns a collection of entry points. Entry points are represented by EntryPoint instances; each EntryPoint 拥有 .name , .group ，和 .value attributes and a .load() method to resolve the value. There are also .module , .attr ，和 .extras attributes for getting the components of the .value 属性。

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 拥有 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 对象。见 backports.entry_points_selectable for compatibility options.

分发元数据 ¶

Every Distribution Package includes some metadata, which you can extract using the metadata() 函数： 

>>> 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.*'

注意

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 .

3.10 版改变： The Description is now included in the metadata when presented through the payload. Line continuation characters have been removed.

The json 属性被添加。

分发版本 ¶

The version() function is the quickest way to get a Distribution Package ’s version number, as a string: 

>>> version('wheel')
'0.32.3'

分发文件 ¶

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 ， pathlib.PurePath derived object with additional dist , size ，和 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

还可以使用 locate method to get a 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() 将返回 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.

分发要求 ¶

To get the full set of requirements for a Distribution Package ，使用 requires() 函数： 

>>> requires('wheel')
["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]

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.

Added in version 3.10.

分布 ¶

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 实例： 

>>> from importlib.metadata import distribution
>>> dist = distribution('wheel')

Thus, an alternative way to get the version number is through the Distribution 实例： 

>>> dist.version
'0.32.3'

There are all kinds of additional metadata available on the Distribution 实例： 

>>> 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 Core metadata specifications 了解额外细节。

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 bytes objects on sys.path .

  • importlib.metadata will incidentally honor pathlib.Path objects on sys.path even though such values will be ignored for imports.

扩展搜索算法 ¶

因为 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 元路径查找器 on sys.meta_path .

默认情况下 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 在 find_distributions() 方法。

内容表

  • importlib.metadata – Accessing package metadata
    • 概述
    • 函数式 API
      • 入口点
      • 分发元数据
      • 分发版本
      • 分发文件
      • 分发要求
      • Mapping import to distribution packages
    • 分布
    • Distribution Discovery
    • 扩展搜索算法

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