importlib.metadata を使う

バージョン 3.8 で追加.

Source code: Lib/importlib/


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.


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')  

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



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.

>>> 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 == 'wheel'][0]  
>>> wheel  
EntryPoint(name='wheel', value='wheel.cli:main', group='console_scripts')
>>> 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 entrypoints, their definition, and usage.


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.*'


The version() function is the quickest way to get a distribution's version number, as a string:

>>> version('wheel')  


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.Path derived object with additional dist, size, and hash properties as indicated by the metadata. For example:

>>> util = [p for p in files('wheel') if '' in str(p)][0]  
>>> util  
>>> util.size  
>>> util.dist  
<importlib.metadata._hooks.PathDistribution object at 0x101e0cef0>
>>> util.hash  
<FileHash mode: sha256 value: bYkw5oMccfazVCoYQwKkkemoVyMAFoR34mmKBx8R1NI>


>>> print(util.read_text())  
import base64
import sys
def as_bytes(s):
    if isinstance(s, text_type):
        return s.encode('utf-8')
    return s

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.


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'"]


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  

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']  

The full set of available metadata is not described here. See PEP 566 for additional details.


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 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:

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 names to match and may supply other relevant context.

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。



Technically, the returned distribution metadata object is an email.message.EmailMessage instance, 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.