importlib.metadata – Accessing package metadata

Нове в версії 3.8.

Змінено в версії 3.10: importlib.metadata більше не є тимчасовим.

Вихідний код: 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.

Важливо

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.

Дивись також

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.

Огляд

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

Ви можете отримати рядок версії для wheel, виконавши наступне:

(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.

Ви можете отримати метадані для дистрибутива:

>>> 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']

Ви також можете отримати номер версії дистрибутива, перелічити його складові файли та отримати список Вимоги до розповсюдження дистрибутива.

Функціональний API

Цей пакет забезпечує такі функції через свій загальнодоступний API.

Точки входу

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.

Запитувати всі точки входу:

>>> 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')  

Виберіть певний сценарій під назвою «колесо» (знаходиться в проекті колеса):

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

Аналогічно, запитайте цю точку входу під час вибору:

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

Огляньте вирішену точку входу:

>>> 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. For compatibility, if no parameters are passed to entry_points, a SelectableGroups object is returned, implementing that dict interface. In the future, calling entry_points with no parameters will return an EntryPoints object. Users should rely on the selection interface to retrieve entry points by group.

Метадані розповсюдження

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, 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.*'

Примітка

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.

Змінено в версії 3.10: Опис тепер включено в метадані, коли представлено через корисне навантаження. Символи продовження рядка видалено.

Додано атрибут json.

Версії розповсюдження

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

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

Файли розповсюдження

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, 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>

Отримавши файл, ви також можете прочитати його вміст:

>>> 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()  
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.

Вимоги до розповсюдження

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

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'], ...}

Нове в версії 3.10.

Розподіл

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 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 Core metadata specifications for additional details.

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 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.

Розширення алгоритму пошуку

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.

Абстрактний клас importlib.abc.MetaPathFinder визначає інтерфейс, очікуваний від шукачів системою імпорту Python. importlib.metadata розширює цей протокол, шукаючи необов’язковий find_distributions, викликаний у шукачах з sys.meta_path, і представляє цей розширений інтерфейс як DistributionFinder абстрактний базовий клас, який визначає цей абстрактний метод:

@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``.
    """

Об’єкт DistributionFinder.Context надає властивості .path і .name, що вказують шлях для пошуку та ім’я, яке відповідає, і може надати інший відповідний контекст.

На практиці це означає, що для підтримки пошуку метаданих пакетів дистрибутива в місцях, відмінних від файлової системи, створіть підклас Distribution і реалізуйте абстрактні методи. Потім із спеціального засобу пошуку поверніть екземпляри цього похідного Distribution у методі find_distributions().