"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 provides the entry point and
metadata APIs that were previously exposed by the now-removed
"pkg_resources" package. Along with "importlib.resources", it
supersedes "pkg_resources".

"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:

  これらはPythonコード内でインポートできるトップレベルの *パッケージ*
  名と *必ずしも* 同等であったり、1:1 で対応するものではありません。1
  つの *配布パッケージ* は複数の *パッケージ* (および単一のモジュール)
  を含むことができ、1つのトップレベルの *パッケージ* は、それが名前空
  間パッケージであれば複数の *配布パッケージ* にマップすることができま
  す。これらのマッピングを得るには packages_distributions()  を使用し
  ます。

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.


機能 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.

バージョン 3.12 で変更: 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.

バージョン 3.13 で変更: "EntryPoint" objects no longer present a
tuple-like interface ("__getitem__()").


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
   distribution 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'

For editable packages, an "origin" property may present **PEP 610**
metadata:

   >>> 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: The ".origin" property was added.


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。


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.

The abstract class "importlib.abc.MetaPathFinder" defines the
interface expected of finders by Python's import system.
"importlib.metadata" extends this protocol by looking for an optional
"find_distributions" callable on the finders from "sys.meta_path" and
presents this extended interface as the "DistributionFinder" abstract
base class, which defines this abstract method:

   @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.


使用例
------

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(...)))

That importer now presumably provides importable modules from a
database, but it provides no metadata or entry points. For this custom
importer to provide metadata, it would also need to implement
"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)

In this way, "query_distributions" would return records for each
distribution served by the database matching the query. For example,
if "requests-1.0" is in the database, "find_distributions" would yield
a "DatabaseDistribution" for "Context(name='requests')" or
"Context(name=None)".

For the sake of simplicity, this example ignores "context.path". The
"path" attribute defaults to "sys.path" and is the set of import paths
to be considered in the search. A "DatabaseImporter" could potentially
function without any concern for a search path. Assuming the importer
does no partitioning, the "path" would be irrelevant. In order to
illustrate the purpose of "path", the example would need to illustrate
a more complex "DatabaseImporter" whose behavior varied depending on
"sys.path"/"PYTHONPATH". In that case, the "find_distributions" should
honor the "context.path" and only yield "Distribution"s pertinent to
that path.

"DatabaseDistribution", then, would look something like:

   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")

This basic implementation should provide metadata and entry points for
packages served by the "DatabaseImporter", assuming that the "record"
supplies suitable ".name", ".version", and ".entry_points" attributes.

The "DatabaseDistribution" may also provide other metadata files, like
"RECORD" (required for "Distribution.files") or override the
implementation of "Distribution.files". See the source for more
inspiration.
