# `importlib.metadata` -- パッケージメタデータへのアクセス

Added in version 3.8.

バージョン 3.10 で変更: `importlib.metadata` は暫定的なものではなくなりました。

ソースコード: 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` は、Pythonの `site-packages` ディレクトリに pip などのツールでインストールしたサードパーティの 配布パッケージ に対して動作します。具体的には、 `dist-info` や `egg-info` ディレクトリを持つ配布物や、 コアとなるメタデータの仕様 で定義されたメタデータを検出できるようにします。

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.

参考

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

  `importlib_metadata` のドキュメントは `importlib.metadata` のバックポートです。これには、このモジュールのクラスと関数の APIリファレンス と、 `pkg_resources` の既存のユーザーのための 移行ガイド があります。

## 概要

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

以下のように実行することで、`wheel` のバージョン文字列を取得することができます:

    (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.

ディストリビューションのメタデータ を取得することができます。:

    >>> 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']

また、 配布物のバージョン番号 を取得し、 構成ファイル をリストアップし、配布物の 配布物の要件 のリストを取得することができます。

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.

## 関数 API

本パッケージは、公開APIを通じて以下の機能を提供します。

### エントリポイント

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 identified 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.

すべてのエントリポイントに問い合わせる:

    >>> 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')

"wheel" という名前の特定のスクリプトを選択します。(wheelプロジェクトにあります):

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

同様に、選択時にそのエントリポイントを問い合わせます:

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

解決したエントリポイントを検証する:

    >>> 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` object. See backports.entry_points_selectable for compatibility options.

### 配布物メタデータ

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.

バージョン 3.10 で変更: ペイロードを通して提示されるとき、 `Description` がメタデータに含まれるようになりました。行の継続文字は削除されました。

`json` 属性が追加されました。

### 配布物バージョン

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'

### 配布物ファイル

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>

ファイルを取得したら、その内容を読むこともできます:

    >>> 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.

### 配布物の要件

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.

インポート可能なトップレベルのPythonモジュールまたは パッケージ を提供する 配布パッケージ 名(名前空間パッケージの場合はその名前)を解決する便利なメソッドです:

    >>> 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 concrete `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.

## Distribution Discovery

デフォルトでは、このパッケージは組み込みで、ファイルシステムおよび zip ファイル 配布パッケージ のメタデータを発見するためのサポートを提供します。このメタデータ検索のデフォルトは `sys.path` ですが、その値をどのように解釈するかは、他のインポート機構が行う方法とは若干異なります。具体的には:

- `importlib.metadata` は `sys.path` の `bytes` オブジェクトを受け入れません。

- `importlib.metadata` は、インポート時には無視されますが、 `sys.path` 上の `pathlib.Path` オブジェクトを優先的に使用します。

## 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.

抽象クラス `importlib.abc.MetaPathFinder` はPythonの importシステムによってファインダーに期待されるインターフェイスを定義しています。 `importlib.metadata` はこのプロトコルを拡張し、 `sys.meta_path` からファインダーにオプションの `find_distributions` を呼び出すことができるようにし、この拡張インターフェースを `DistributionFinder` 抽象基底クラスとして提示し、この抽象メソッドを定義しています:

    @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.