importlib.metadata -- 访问软件包元数据

Added in version 3.8.

在 3.10 版本发生变更: importlib.metadata 不再是暂定的。

源代码: Lib/importlib/metadata/__init__.py

importlib.metadata 是一个提供对已安装的 分发包 的元数据的访问的库，如其入口点或其顶层名称 (导入包, 模块等，如果存在的话）。 这个库部分构建于 Python 的导入系统之上，其目标是取代 pkg_resources 的中的 entry point API 和 metadata API。 配合 importlib.resources ，这个包使得较老旧且低效的 pkg_resources 包不再必要。

importlib.metadata 对 pip 等工具安装到 Python 的 site-packages 目录的第三方 分发包 进行操作。 具体来说，适用的分发包应带有可发现的 dist-info 或 egg-info 目录，以及 核心元数据规范说明 定义的元数据。

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.

分发包元数据默认可存在于 sys.path 下的文件系统或 zip 归档文件中。通过一个扩展机制，元数据可以存在于几乎任何地方。

参见

https://importlib-metadata.readthedocs.io/

importlib_metadata 的文档，它向下移植了 importlib.metadata。它包含该模块的类和函数的 API 参考，以及针对 pkg_resources 现有用户的 迁移指南。

概述

让我们假设你想要获取你使用 pip 安装的某个 分发包 的版本字符串。我们首先创建一个虚拟环境并在其中安装一些软件包：

$ python -m venv example
$ source example/bin/activate
(example) $ python -m pip install wheel

你可以通过运行以下代码得到 wheel 的版本字符串：

(example) $ python
>>> from importlib.metadata import version  
>>> version('wheel')  
'0.32.3'

你还能得到可通过 EntryPoint 的属性 (通常为 'group' 或 'name') 来选择的入口点多项集，比如 console_scripts, distutils.commands。 每个 group 包含一个由 EntryPoint 对象组成的多项集。

你可以获得 分发的元数据：

>>> 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']

你也可以获得 分发包的版本号，列出它的 构成文件，并且得到分发包的 分发包的依赖 列表。

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.

函数式 API

这个包的公开 API 提供了以下功能。

入口点

importlib.metadata.entry_points(**select_params)

Returns a EntryPoints instance describing entry points for the current environment. Any given keyword parameters are passed to the select() 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 different Distribution 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.

查询所有的入口点：

>>> 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')

选出命名为 “wheel” 的特定脚本（可以在 wheel 项目中找到）：

>>> 'wheel' in scripts.names  
True
>>> wheel = scripts['wheel']

等价地，在选择过程中查询对应的入口点：

>>> (wheel,) = entry_points(group='console_scripts', name='wheel')  
>>> (wheel,) = entry_points().select(group='console_scripts', name='wheel')

检查解析得到的入口点：

>>> 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>

group 和 name 是由包作者定义的任意值并且通常来说客户端会想要解析特定 group 的所有入口点。 请参阅 the setuptools docs 了解有关入口点，其定义和用法的更多信息。

兼容性说明

"selectable" 入口点是在 importlib_metadata 3.6 和 Python 3.10 中引入的。 在这项改变之前，entry_points 不接受任何形参并且总是返回一个由入口点组成的字典，字典的键为分组名。 在 importlib_metadata 5.0 和 Python 3.12 中，entry_points 总是返回一个 EntryPoints 对象。 请参阅 backports.entry_points_selectable 了解相关兼容性选项。

分发的元数据

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 PackageMetadata protocol.

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.

在 3.10 版本发生变更: 当有效载荷中包含时，Description 以去除续行符的形式被包含于元数据中。

添加了 json 属性。

分发包的版本

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'

分发包的文件

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 additional dist, size, and hash 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>

当你获得了文件对象，你可以读取其内容：

>>> 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.

分发包的依赖

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'"]

将导入映射到分发包

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.

解析每个提供可导入的最高层级 Python 模块或 导入包 对应的 分发包 名称（对于命名空间包可能有多个名称）的快捷方法:

>>> packages_distributions()
{'importlib_metadata': ['importlib-metadata'], 'yaml': ['PyYAML'], 'jaraco': ['jaraco.classes', 'jaraco.functools'], ...}

某些可编辑的安装 没有提供最高层级名称，因而此函数不适用于这样的安装。

Added in version 3.10.

分发包对象

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'

The full set of available metadata is not described here. See the PyPA Core metadata specification for additional details.

分发包的发现

在默认情况下，这个包针对文件系统和 zip 文件 分发包 的元数据发现提供了内置支持。 这个元数据查找器的搜索目标默认为 sys.path，但它对来自其他导入机制行为方式的解读会略有变化。 特别地:

  • importlib.metadata 不会识别 sys.path 上的 bytes 对象。

  • importlib.metadata 将顺带识别 sys.path 上的 pathlib.Path 对象，即使这些值会被导入操作所忽略。

扩展搜索算法

因为 分发包 元数据不能通过 sys.path 搜索，或是通过包加载器直接获得，一个分发包的元数据是通过导入系统的 查找器 找到的。 要找到分发包的元数据，importlib.metadata 将在 sys.meta_path 上查询 元路径查找器 的列表。

在默认情况下 importlib.metadata 会安装在文件系统中找到的分发包的查找器。 这个查找器无法真正找出任何 分发包，但它能找到它们的元数据。

抽象基类 importlib.abc.MetaPathFinder 定义了 Python 导入系统期望的查找器接口。 importlib.metadata 通过寻找 sys.meta_path 上查找器可选的 find_distributions 可调用的属性扩展这个协议，并将这个扩展接口作为 DistributionFinder 抽象基类提供，它定义了这个抽象方法：

@abc.abstractmethod
def find_distributions(context=DistributionFinder.Context()):
    """返回一个由所有能够为指定 ``context`` 加载包的元数据的
    Distribution 实例组成的可迭代对象。
    """

DistributionFinder.Context 对象提供了指示搜索路径和匹配名称的属性 .path 和 .name ，也可能提供其他相关的上下文。

这在实践中意味着要支持在文件系统外的其他位置查找分发包的元数据，你需要子类化 Distribution 并实现抽象方法，之后从一个自定义查找器的 find_distributions() 方法返回这个派生的 Distribution 实例。