importlib.metadata – Acceso a los metadatos de los paquetes¶
Added in version 3.8.
Distinto en la versión 3.10: importlib.metadata ya no es 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.
Importante
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 packages_distributions() to get a mapping between them.
Por defecto, los metadatos de distribución pueden vivir en el sistema de ficheros o en archivos zip en sys.path. A través de un mecanismo de extensión, los metadatos pueden vivir casi en cualquier lugar.
Ver también
- https://importlib-metadata.readthedocs.io/
La documentación de
importlib_metadata, que proporciona un backport deimportlib.metadata. Esto incluye una Referencia API para las clases y funciones de este módulo, así como una Guía de migración para los usuarios existentes depkg_resources.
Descripción general¶
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
Se puede obtener la cadena de versión para wheel ejecutando lo siguiente:
(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.
Se pueden obtener los metadatos para una distribución:
>>> 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']
También se puede obtener el número de versión de una distribución, enumerar sus archivos constituyentes y obtener una lista de los Requerimientos de la distribución de la distribución.
- exception importlib.metadata.PackageNotFoundError¶
Subclass of
ModuleNotFoundErrorraised by several functions in this module when queried for a distribution package which is not installed in the current Python environment.
API funcional¶
Este paquete provee la siguiente funcionalidad a través de su API pública.
Puntos de entrada¶
- importlib.metadata.entry_points(**select_params)¶
Returns a
EntryPointsinstance describing entry points for the current environment. Any given keyword parameters are passed to theselect()method for comparison to the attributes of the individual entry point definitions.Note: it is not currently possible to query for entry points based on their
EntryPoint.distattribute (as differentDistributioninstances do not currently compare equal, even if they have the same attributes)
- class importlib.metadata.EntryPoints¶
Details of a collection of installed entry points.
Also provides a
.groupsattribute that reports all identified entry point groups, and a.namesattribute that reports all identified entry point names.
- class importlib.metadata.EntryPoint¶
Details of an installed entry point.
Each
EntryPointinstance has.name,.group, and.valueattributes and a.load()method to resolve the value. There are also.module,.attr, and.extrasattributes for getting the components of the.valueattribute, and.distfor obtaining information regarding the distribution package that provides the entry point.
Consultar todos los puntos de entrada:
>>> eps = entry_points()
The entry_points() function returns a 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')
Elige un script específico llamado «wheel» (que se encuentra en el proyecto wheel):
>>> 'wheel' in scripts.names
True
>>> wheel = scripts['wheel']
De manera equivalente, consulta por ese punto de entrada durante la selección:
>>> (wheel,) = entry_points(group='console_scripts', name='wheel')
>>> (wheel,) = entry_points().select(group='console_scripts', name='wheel')
Inspeccionar el punto de entrada resuelto:
>>> 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.
Distinto en la versión 3.12: 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. With importlib_metadata 5.0 and Python 3.12,
entry_points always returns an EntryPoints object. See
backports.entry_points_selectable
for compatibility options.
Distinto en la versión 3.13: EntryPoint objects no longer present a tuple-like interface
(__getitem__()).
Metadatos de distribución¶
- importlib.metadata.metadata(distribution_name)¶
Return the distribution metadata corresponding to the named distribution package as a
PackageMetadatainstance.Raises
PackageNotFoundErrorif the named distribution package is not installed in the current Python environment.
- class importlib.metadata.PackageMetadata¶
A concrete implementation of the PackageMetadata protocol.
In addition to providing the defined protocol methods and attributes, subscripting the instance is equivalent to calling the
get()method.
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 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.*'
The full set of available metadata is not described here. See the PyPA Core metadata specification for additional details.
Distinto en la versión 3.10: La Descripción ahora se incluye en los metadatos cuando se presenta a través de la carga útil. Se han eliminado los caracteres de continuación de línea.
El atributo json fue añadido.
Versiones de distribución¶
- importlib.metadata.version(distribution_name)¶
Return the installed distribution package version for the named distribution package.
Raises
PackageNotFoundErrorif the named distribution package is not installed in the current Python environment.
The version() function is the quickest way to get a
Distribution Package’s version
number, as a string:
>>> version('wheel')
'0.32.3'
Archivos de distribución¶
- importlib.metadata.files(distribution_name)¶
Return the full set of files contained within the named distribution package.
Raises
PackageNotFoundErrorif the named distribution package is not installed in the current Python environment.Returns
Noneif the distribution is found but the installation database records reporting the files associated with the distribuion package are missing.
- class importlib.metadata.PackagePath¶
A
pathlib.PurePathderived object with additionaldist,size, andhashproperties corresponding to the distribution package’s installation metadata for that file.
The files() function takes a
Distribution Package
name and returns all of the files installed by this distribution. Each file is reported
as a PackagePath instance. 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>
Una vez que se tiene el archivo, también se puede leer su contenido:
>>> 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 the absolute
path to the file:
>>> 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.
Requerimientos de la distribución¶
- importlib.metadata.requires(distribution_name)¶
Return the declared dependency specifiers for the named distribution package.
Raises
PackageNotFoundErrorif the named distribution package is not installed in the current Python environment.
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'"]
Mapeo de paquetes de importación a distribución¶
- importlib.metadata.packages_distributions()¶
Return a mapping from the top level module and import package names found via
sys.meta_pathto the names of the distribution packages (if any) that provide the corresponding files.To allow for namespace packages (which may have members provided by multiple distribution packages), each top level import name maps to a list of distribution names rather than mapping directly to a single name.
Un método práctico para resolver el nombre del Paquete de distribución (o nombres, en el caso de un paquete de espacio de nombres) que proporciona cada módulo Python de nivel superior importable o Paquete de importación:
>>> packages_distributions()
{'importlib_metadata': ['importlib-metadata'], 'yaml': ['PyYAML'], 'jaraco': ['jaraco.classes', 'jaraco.functools'], ...}
Algunas instalaciones editables, no suministran nombres de nivel superior, por lo que esta función no es fiable con dichas instalaciones.
Added in version 3.10.
Distribuciones¶
- importlib.metadata.distribution(distribution_name)¶
Return a
Distributioninstance describing the named distribution package.Raises
PackageNotFoundErrorif the named distribution package is not installed in the current Python environment.
- class importlib.metadata.Distribution¶
Details of an installed distribution package.
Note: different
Distributioninstances do not currently compare equal, even if they relate to the same installed distribution and accordingly have the same attributes.
While the module level API described above is the most common and convenient usage,
you can get all of that information from the Distribution class.
Distribution is an abstract object that represents the metadata for
a Python Distribution Package.
You can get the concrete Distribution subclass instance for an installed
distribution package by calling the distribution() function:
>>> from importlib.metadata import distribution
>>> dist = distribution('wheel')
>>> type(dist)
<class 'importlib.metadata.PathDistribution'>
Thus, an alternative way to get the version number is through the
Distribution instance:
>>> dist.version
'0.32.3'
There are all kinds of additional metadata available on Distribution
instances:
>>> dist.metadata['Requires-Python']
'>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
>>> dist.metadata['License']
'MIT'
For editable packages, an origin property may present PEP 610
metadata:
>>> dist.origin.url
'file:///path/to/wheel-0.32.3.editable-py3-none-any.whl'
The full set of available metadata is not described here. See the PyPA Core metadata specification for additional details.
Added in version 3.13: The .origin property was added.
Distribution Discovery¶
Por defecto, este paquete proporciona soporte incorporado para el descubrimiento de metadatos para el sistema de archivos y archivos zip Distribution Packages. Este buscador de metadatos busca por defecto sys.path, pero varía ligeramente en cómo interpreta esos valores respecto a cómo lo hace otra maquinaria de importación. En particular:
importlib.metadatadoes not honorbytesobjects onsys.path.importlib.metadatarespetará incidentalmente los objetospathlib.Path`ensys.pathaunque tales valores serán ignorados para las importaciones.
Extendiendo el algoritmo de búsqueda¶
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.
Por defecto importlib.metadata instala un buscador de paquetes de distribución encontrados en el sistema de ficheros. Este buscador en realidad no encuentra ninguna distribución, pero puede encontrar sus metadatos.
La clase abstracta importlib.abc.MetaPathFinder define la interfaz que se espera de los buscadores por el sistema de importación de Python. importlib.metadata amplía este protocolo buscando una find_distributions opcional invocable en los buscadores desde sys.meta_path y presenta esta interfaz extendida como la clase base abstracta DistributionFinder, que define este método abstracto:
@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``.
"""
El objeto DistributionFinder.Context proporciona propiedades .path y .name que indican la ruta de búsqueda y los nombres que deben coincidir y puede proporcionar otro contexto relevante.
Lo que esto significa en la práctica es que, para soportar la búsqueda de metadatos en paquetes de distribución en ubicaciones distintas al sistema de archivos, se debe subclasificar Distribution e implementar sus métodos abstractos. Luego, en el método find_distributions() de un buscador personalizado no hay más que retornar instancias de esta Distribution derivada.
Example¶
Consider for example a custom finder that loads Python modules from a database:
class DatabaseImporter(importlib.abc.MetaPathFinder):
def __init__(self, db):
self.db = db
def find_spec(self, fullname, target=None) -> ModuleSpec:
return self.db.spec_from_name(fullname)
sys.meta_path.append(DatabaseImporter(connect_db(...)))
That importer now presumably provides importable modules from a
database, but it provides no metadata or entry points. For this
custom importer to provide metadata, it would also need to implement
DistributionFinder:
from importlib.metadata import DistributionFinder
class DatabaseImporter(DistributionFinder):
...
def find_distributions(self, context=DistributionFinder.Context()):
query = dict(name=context.name) if context.name else {}
for dist_record in self.db.query_distributions(query):
yield DatabaseDistribution(dist_record)
In this way, query_distributions would return records for
each distribution served by the database matching the query. For
example, if requests-1.0 is in the database, find_distributions
would yield a DatabaseDistribution for Context(name='requests')
or Context(name=None).
For the sake of simplicity, this example ignores context.path. The
path attribute defaults to sys.path and is the set of import paths to
be considered in the search. A DatabaseImporter could potentially function
without any concern for a search path. Assuming the importer does no
partitioning, the «path» would be irrelevant. In order to illustrate the
purpose of path, the example would need to illustrate a more complex
DatabaseImporter whose behavior varied depending on
sys.path/PYTHONPATH. In that case, the find_distributions should
honor the context.path and only yield Distributions pertinent to that
path.
DatabaseDistribution, then, would look something like:
class DatabaseDistribution(importlib.metadata.Distribution):
def __init__(self, record):
self.record = record
def read_text(self, filename):
"""
Read a file like "METADATA" for the current distribution.
"""
if filename == "METADATA":
return f"""Name: {self.record.name}
Version: {self.record.version}
"""
if filename == "entry_points.txt":
return "\n".join(
f"""[{ep.group}]\n{ep.name}={ep.value}"""
for ep in self.record.entry_points)
def locate_file(self, path):
raise RuntimeError("This distribution has no file system")
This basic implementation should provide metadata and entry points for
packages served by the DatabaseImporter, assuming that the
record supplies suitable .name, .version, and
.entry_points attributes.
The DatabaseDistribution may also provide other metadata files, like
RECORD (required for Distribution.files) or override the
implementation of Distribution.files. See the source for more inspiration.