Using importlib.metadata¶
Novo na versão 3.8.
Source code: Lib/importlib/metadata.py
Nota
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.
Visão Geral¶
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
Você pode obter a string de versão para wheel executando o seguinte:
(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.
Você pode obter os metadados para uma distribuição:
>>> 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']
Você também pode obter uma número da versão da distribuição, listar seus arquivos constituintes e obter uma lista dos Requisitos de distribuição da distribuição.
API funcional¶
Este pacote fornece a seguinte funcionalidade por meio de sua API pública.
Pontos de entrada¶
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 ep.name == '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.
Metadados de distribuição¶
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.*'
Versões de distribuição¶
The version() function is the quickest way to get a distribution’s version
number, as a string:
>>> version('wheel')
'0.32.3'
Arquivos de distribuição¶
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 '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>
Uma vez que tenha o arquivo, você também pode ler seu conteúdo:
>>> print(util.read_text())
import base64
import sys
...
def as_bytes(s):
if isinstance(s, text_type):
return s.encode('utf-8')
return s
No caso em que o arquivo de metadados que lista os arquivos (RECORD ou SOURCES.txt) estiver faltando, files() retornará None. O chamador pode querer agrupar chamadas para files() em always_iterable ou de outra forma se proteger contra isso condição se a distribuição de destino não for conhecida por ter os metadados presentes.
Requisitos de distribuição¶
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'"]
Distribuições¶
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')
Assim, uma forma alternativa de obter o número da versão é através da instância Distribution:
>>> dist.version
'0.32.3'
Existem todos os tipos de metadados adicionais disponíveis na instância Distribution:
>>> 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.
Estendendo o algoritmo de pesquisa¶
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.
A classe abstrata importlib.abc.MetaPathFinder define a interface esperada dos localizadores pelo sistema de importação do Python. importlib.metadata estende este protocolo procurando por um chamável find_distributions opcional nos localizadores de sys.meta_path e apresenta esta interface estendida como a classe base abstrata DistributionFinder, que define este método abstrato:
@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``.
"""
The DistributionFinder.Context object provides .path and .name
properties indicating the path to search and names to match and may
supply other relevant context.
O que isso significa na prática é que para prover suporte à localização de metadados de pacotes de distribuição em outros locais fora do sistema de arquivos, crie uma subclasse Distribution e implemente os métodos abstratos. Então, a partir de um localizador personalizado, retorne instâncias deste derivado de Distribution no método find_distributions().
Notas de rodapé
- 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.