`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 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 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

它们 不一定 等同或 1:1 对应于可在 Python 代码中导入的顶层 导入包 名称。一个 分发包 可以包含多个 导入包 (和单个模块)，如果是命名空间包，一个顶层 导入包 可以映射到多个 分发包。您可以使用 packages_distributions() 来获取它们之间的映射。

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.

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¶

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

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'

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.

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()  

entry_points() 函数返回一个 EntryPoints 对象，即由带 names 和 groups 属性的所有 EntryPoint 对象组成的多项集以方便使用:

>>> sorted(eps.groups)  
['console_scripts', 'distutils.commands', 'distutils.setup_keywords', 'egg_info.writers', 'setuptools.installation']

EntryPoints 具有 select() 方法用于选择匹配指定特征属性的入口点。如选择 console_scripts 组中的入口点:

>>> scripts = eps.select(group='console_scripts')  

效果相同，因为 entry_points() 会传递关键字参数来选择:

>>> 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>

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.

在 3.12 版本发生变更: "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。

在 3.13 版本发生变更: EntryPoint 对象不再提供类似于元组的接口（__getitem__()）。

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.

每个分发包都包括一些元数据，你可以使用 metadata() 函数来获取:

>>> 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)¶

返回指定分发包的已安装分发包版本。

Raises PackageNotFoundError if the named distribution package is not installed in the current Python environment.

version() 函数是获取字符串形式的分发包版本号的最快速方式:

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

分发包的文件¶

importlib.metadata.files(distribution_name)¶

返回包含在指定分发包内的完整文件集合。

Raises PackageNotFoundError if the named distribution package is not installed in the current Python environment.

如果找到了分发包但未找到报告与分发包相关联的文件的安装数据库记录则返回 None。

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'

对于可编辑包，origin 属性可能表示 PEP 610 元数据：

>>> 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: 增加了 .origin 特征属性。

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。

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 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.

The implementation has hooks integrated into the PathFinder, serving metadata for distribution packages found on the file system.

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()) -> Iterable[Distribution]:
    """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 sought by the consumer.

In practice, 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.

示例¶

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(...)))

该导入器现在大概可以从数据库中导入模块，但它不提供元数据或入口点。这个自定义导入器如果要提供元数据，它还需要实现 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)

这样一来，query_distributions 就会返回数据库中与查询匹配的每个分发包的记录。例如，如果数据库中有 requests-1.0，find_distributions 就会为 Context(name='requests') 或``Context(name=None)`` 产生 DatabaseDistribution。

为简单起见，本例忽略了 context.path。path 属性默认为 sys.path，是搜索中考虑的导入路径集。一个 DatabaseImporter 可以在不考虑搜索路径的情况下运作。假设导入器不进行分区，那么 "path" 就无关紧要了。为了说明 path 的作用，示例需要展示一个更复杂的 DatabaseImporter，它的行为随 sys.path/PYTHONPATH 而变化。在这种情况下，find_distributions 应该尊重 context.path，并且只产生与该路径相关的 Distribution。

那么，DatabaseDistribution 看起来就像是这样：

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")

这个基本实现应当为由 DatabaseImporter 进行服务的包提供元数据和入口点，假定 record 提供了适当的 .name, .version 和 .entry_points 属性。

DatabaseDistribution 还可能提供其他元数据文件，比如 RECORD (对 Distribution.files 来说需要) 或重写 Distribution.files 的实现。请参看源代码深入了解。

`importlib.metadata` -- 访问软件包元数据¶

概述¶

函数式 API¶

入口点¶

分发的元数据¶

分发包的版本¶

分发包的文件¶

分发包的依赖¶

将导入映射到分发包¶

分发包对象¶

分发包的发现¶

Implementing Custom Providers¶

示例¶

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importlib.metadata -- 访问软件包元数据¶

概述¶

函数式 API¶

入口点¶

分发的元数据¶

分发包的版本¶

分发包的文件¶

分发包的依赖¶

将导入映射到分发包¶

分发包对象¶

分发包的发现¶

Implementing Custom Providers¶

示例¶

`importlib.metadata` -- 访问软件包元数据¶