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

バージョン 3.8 で追加.

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` 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.

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。

## 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

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.

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 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')

"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. 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.

### 配布物メタデータ

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.*'

注釈

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.

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

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

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>

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 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.

### 配布物の要件

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

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'], ...}

バージョン 3.10 で追加.

## Distributions

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

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.