importlib.metadata 사용하기

버전 3.8에 추가.

버전 3.10에서 변경: importlib.metadata is no longer provisional.

Source code: 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.

중요

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.

더 보기

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

The documentation for importlib_metadata, which supplies a backport of importlib.metadata. This includes an API reference for this module’s classes and functions, as well as a migration guide for existing users of pkg_resources.

개요

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:

$ python3 -m venv example
$ source example/bin/activate
(example) $ python -m pip install wheel

다음을 실행하여 wheel에 대한 버전 문자열을 얻을 수 있습니다:

(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.

여러분은 배포 메타데이터를 얻을 수 있습니다:

>>> 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']

또한 배포의 버전 번호를 가져오고, 구성 파일을 나열하고, 배포의 요구사항 리스트를 얻을 수 있습니다.

기능적 API

이 패키지는 공용 API를 통해 다음과 같은 기능을 제공합니다.

진입 지점

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.

Query all entry points:

>>> 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')  

Pick out a specific script named “wheel” (found in the wheel project):

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

Equivalently, query for that entry point during selection:

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

Inspect the resolved entry point:

>>> 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.

배포 메타데이터

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.*'

참고

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.

버전 3.10에서 변경: The Description is now included in the metadata when presented through the payload. Line continuation characters have been removed.

버전 3.10에 추가: The json attribute was added.

배포 버전

The version() function is the quickest way to get a Distribution Package’s version number, as a string:

>>> version('wheel')  
'0.32.3'

배포 파일

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>

일단 파일을 얻으면, 내용을 읽을 수도 있습니다:

>>> 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')

메타 데이터 파일 목록 파일(RECORD나 SOURCES.txt)이 누락된 경우, files()None을 반환합니다. 대상 배포에 메타 데이터가 있음이 알려지지 않았을 때, 이 조건에 대한 보호로 호출자는 files()에 대한 호출을 always_iterable이나 다른 것으로 감쌀 수 있습니다.

배포 요구 사항

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

A convenience method to resolve the Distribution Package name (or names, in the case of a namespace package) that provide each importable top-level Python module or Import Package:

>>> packages_distributions()
{'importlib_metadata': ['importlib-metadata'], 'yaml': ['PyYAML'], 'jaraco': ['jaraco.classes', 'jaraco.functools'], ...}

버전 3.10에 추가.

배포

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')  

따라서, 버전 번호를 얻는 다른 방법은 Distribution 인스턴스를 사용하는 것입니다:

>>> dist.version  
'0.32.3'

Distribution 인스턴스에서 사용할 수 있는 모든 종류의 추가 메타 데이터가 있습니다:

>>> 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

By default, this package provides built-in support for discovery of metadata for file system and zip file Distribution Packages. This metadata finder search defaults to sys.path, but varies slightly in how it interprets those values from how other import machinery does. In particular:

  • importlib.metadata does not honor bytes objects on sys.path.

  • importlib.metadata will incidentally honor pathlib.Path objects on sys.path even though such values will be ignored for imports.

검색 알고리즘 확장하기

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.

추상 클래스 importlib.abc.MetaPathFinder는 파이썬의 임포트 시스템에 의해 파인더가 기대하는 인터페이스를 정의합니다. importlib.metadatasys.meta_path의 파인더에서 선택적인 find_distributions 콜러블을 조회함으로써 이 프로토콜을 확장하고 이 확장된 인터페이스를 다음과 같은 추상 메서드를 정의하는 DistributionFinder 추상 베이스 클래스로 제공합니다:

@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 객체는 검색할 경로와 일치할 이름을 가리키는 .path.name 프로퍼티를 제공하고 다른 관련 문맥을 제공할 수 있습니다.

이것이 실제로 의미하는 것은, 파일 시스템이 아닌 위치에서 배포 패키지 메타 데이터를 찾는 것을 지원하려면, Distribution을 서브 클래싱하고 추상 메서드를 구현해야 한다는 것입니다. 그런 다음 사용자 정의 파인더의 find_distributions() 메서드에서, 이 파생된 Distribution의 인스턴스를 반환하십시오.