importlib.metadata を使う¶
Source code: Lib/importlib/metadata.py
バージョン 3.8 で追加.
注釈
This functionality is provisional and may deviate from the usual version semantics of the standard library.
importlib.metadata is a library that provides for access to installed
package metadata. 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 in Python 3.7
and newer (backported as importlib_resources for older versions of
Python), this can eliminate the need to use the older and less efficient
pkg_resources package.
By "installed package" we generally mean a third-party package installed into
Python's site-packages directory via tools such as pip. Specifically,
it means a package with either a discoverable dist-info or egg-info
directory, and metadata defined by PEP 566 or its older specifications.
By default, package metadata can live on the file system or in zip archives on
sys.path. Through an extension mechanism, the metadata can live almost
anywhere.
概要¶
Let's say you wanted to get the version string for a package you've installed
using pip. We start by creating a virtual environment and installing
something into it:
$ python3 -m venv example
$ source example/bin/activate
(example) $ 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 the set of entry points keyed by group, such as
console_scripts, distutils.commands and others. Each group contains a
sequence 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。
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¶
The entry_points() function returns a dictionary of all entry points,
keyed by group. 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:
>>> eps = entry_points()
>>> list(eps)
['console_scripts', 'distutils.commands', 'distutils.setup_keywords', 'egg_info.writers', 'setuptools.installation']
>>> scripts = eps['console_scripts']
>>> wheel = [ep for ep in scripts if ep.name == 'wheel'][0]
>>> 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.
配布物メタデータ¶
Every distribution includes some metadata, which you can extract using the
metadata() function:
>>> wheel_metadata = metadata('wheel')
The keys of the returned data structure 1 name the metadata keywords, and their values are returned unparsed from the distribution metadata:
>>> wheel_metadata['Requires-Python']
'>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
配布物バージョン¶
The version() function is the quickest way to get a distribution'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
また、 locate メソッドを使用すると、ファイルへの絶対パスを取得することができます:
>>> 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, use the requires()
function:
>>> requires('wheel')
["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]
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 package. You can
get the Distribution instance:
>>> from importlib.metadata import distribution
>>> dist = distribution('wheel')
したがって、バージョン情報を取得する別の方法として、 Distribution インスタンスを使用します:
>>> dist.version
'0.32.3'
Distribution インスタンスには、あらゆる種類の追加メタデータが用意されています:
>>> 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 PEP 566 for additional details.
検索アルゴリズムの拡張¶
Because package metadata is not available through sys.path searches, or
package loaders directly, the metadata for a package 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 default PathFinder for Python includes a hook that calls into
importlib.metadata.MetadataPathFinder for finding distributions
loaded from typical file-system-based paths.
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``.
"""
DistributionFinder.Context オブジェクトは、検索するパスと一致する名前を示す .path と .name のプロパティを提供し、その他の関連するコンテキストを提供することもできます。
つまり、ファイルシステム以外の場所にある配布パッケージのメタデータを見つけるには、 Distribution をサブクラス化して抽象メソッドを実装します。そして、カスタムファインダーから find_distributions() メソッドで、派生した Distribution のインスタンスを返します。
脚注
- 1
Technically, the returned distribution metadata object is an
email.message.EmailMessageinstance, but this is an implementation detail, and not part of the stable API. You should only use dictionary-like methods and syntax to access the metadata contents.