"importlib.metadata" -- Accessing package metadata
**************************************************

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:

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

다음을 실행하여 "wheel"에 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 요구사
항 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.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()"는 "None"을 반환합니다. 대상 배포에 메타 데이터가 있음이 알려
지지 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 사용하
는 것입니다:

   >>> dist.version  
   '0.32.3'

"Distribution" 인스턴스에서 사용할 수 있는 모든 종류의 추가 메타 데이
터가 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.MetaPathFinder"는 파이썬의 임포트 시스템에
의해 파인더가 기대하는 인터페이스를 정의합니다. "importlib.metadata"는
"sys.meta_path"의 파인더에서 선택적인 "find_distributions" 콜러블을 조
회함으로써 이 프로토콜을 확장하고 이 확장된 인터페이스를 다음과 같은
추상 메서드를 정의하는 "DistributionFinder" 추상 베이스 클래스로 제공
합니다:

   @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 가리키
는 ".path"와 ".name" 프로퍼티를 제공하고 다른 관련 문맥을 제공할 수 있
습니다.

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