collections.abc — Abstract Base Classes for Containers

Added in version 3.3: Anteriormente, este módulo formaba parte del módulo collections.

Código fuente: Lib/_collections_abc.py

This module provides abstract base classes that can be used to test whether a class provides a particular interface; for example, whether it is hashable or whether it is a mapping.

Una prueba issubclass() o isinstance() para una interfaz funciona de tres formas.

1) A newly written class can inherit directly from one of the abstract base classes. The class must supply the required abstract methods. The remaining mixin methods come from inheritance and can be overridden if desired. Other methods may be added as needed:

class C(Sequence):                      # Direct inheritance
    def __init__(self): ...             # Extra method not required by the ABC
    def __getitem__(self, index):  ...  # Required abstract method
    def __len__(self):  ...             # Required abstract method
    def count(self, value): ...         # Optionally override a mixin method

>>> issubclass(C, Sequence)
True
>>> isinstance(C(), Sequence)
True

2) Existing classes and built-in classes can be registered as «virtual subclasses» of the ABCs. Those classes should define the full API including all of the abstract methods and all of the mixin methods. This lets users rely on issubclass() or isinstance() tests to determine whether the full interface is supported. The exception to this rule is for methods that are automatically inferred from the rest of the API:

class D:                                 # No inheritance
    def __init__(self): ...              # Extra method not required by the ABC
    def __getitem__(self, index):  ...   # Abstract method
    def __len__(self):  ...              # Abstract method
    def count(self, value): ...          # Mixin method
    def index(self, value): ...          # Mixin method

Sequence.register(D)                     # Register instead of inherit

>>> issubclass(D, Sequence)
True
>>> isinstance(D(), Sequence)
True

In this example, class D does not need to define __contains__, __iter__, and __reversed__ because the in-operator, the iteration logic, and the reversed() function automatically fall back to using __getitem__ and __len__.

3) Some simple interfaces are directly recognizable by the presence of the required methods (unless those methods have been set to None):

class E:
    def __iter__(self): ...
    def __next__(self): ...

>>> issubclass(E, Iterable)
True
>>> isinstance(E(), Iterable)
True

Las interfaces complejas no admiten esta última técnica porque una interfaz es más que la simple presencia de nombres de métodos. Las interfaces especifican la semántica y las relaciones entre métodos que no se pueden inferir únicamente de la presencia de nombres de métodos específicos. Por ejemplo, saber que una clase proporciona __getitem__, __len__ y __iter__ no es suficiente para distinguir un Sequence de un Mapping.

Added in version 3.9: Estas clases abstractas ahora soportan []. Vea Tipo Alias Genérico y PEP 585.

Colecciones clases base abstractas

El módulo de colecciones ofrece lo siguiente ABCs:

ABC

Hereda de

Métodos abstractos

Métodos mixin

Container [1]

__contains__

Hashable [1]

__hash__

Iterable [1] [2]

__iter__

Iterator [1]

Iterable

__next__

__iter__

Reversible [1]

Iterable

__reversed__

Generator [1]

Iterator

send, throw

close, __iter__, __next__

Sized [1]

__len__

Callable [1]

__call__

Collection [1]

Sized, Iterable, Container

__contains__, __iter__, __len__

Sequence

Reversible, Collection

__getitem__, __len__

__contains__, __iter__, __reversed__, index, and count

MutableSequence

Sequence

__getitem__, __setitem__, __delitem__, __len__, insert

Inherited Sequence methods and append, clear, reverse, extend, pop, remove, and __iadd__

Set

Collection

__contains__, __iter__, __len__

__le__, __lt__, __eq__, __ne__, __gt__, __ge__, __and__, __or__, __sub__, __rsub__, __xor__, __rxor__ and isdisjoint

MutableSet

Set

__contains__, __iter__, __len__, add, discard

Métodos heredados Set y clear, pop, remove, __ior__, __iand__, __ixor__, and __isub__

Mapping

Collection

__getitem__, __iter__, __len__

__contains__, keys, items, values, get, __eq__, and __ne__

MutableMapping

Mapping

__getitem__, __setitem__, __delitem__, __iter__, __len__

Métodos heredados Mapping y pop, popitem, clear, update, and setdefault

MappingView

Sized

__init__, __len__ and __repr__

ItemsView

MappingView, Set

__contains__, __iter__

KeysView

MappingView, Set

__contains__, __iter__

ValuesView

MappingView, Collection

__contains__, __iter__

Awaitable [1]

__await__

Coroutine [1]

Awaitable

send, throw

close

AsyncIterable [1]

__aiter__

AsyncIterator [1]

AsyncIterable

__anext__

__aiter__

AsyncGenerator [1]

AsyncIterator

asend, athrow

aclose, __aiter__, __anext__

Buffer [1]

__buffer__

Notas al pie

Colecciones Clases base abstractas - Descripciones detalladas

class collections.abc.Container

ABC for classes that provide the __contains__() method.

class collections.abc.Hashable

ABC for classes that provide the __hash__() method.

class collections.abc.Sized

ABC for classes that provide the __len__() method.

class collections.abc.Callable

ABC for classes that provide the __call__() method.

See Anotaciones en objetos invocables for details on how to use Callable in type annotations.

class collections.abc.Iterable

ABC for classes that provide the __iter__() method.

Checking isinstance(obj, Iterable) detects classes that are registered as Iterable or that have an __iter__() method, but it does not detect classes that iterate with the __getitem__() method. The only reliable way to determine whether an object is iterable is to call iter(obj).

class collections.abc.Collection

ABC para clases de contenedor iterables de tamaño.

Added in version 3.6.

class collections.abc.Iterator

ABC para clases que proporcionan el método __iter__() y __next__(). Ver también la definición de iterator.

class collections.abc.Reversible

ABC for iterable classes that also provide the __reversed__() method.

Added in version 3.6.

class collections.abc.Generator

ABC for generator classes that implement the protocol defined in PEP 342 that extends iterators with the send(), throw() and close() methods.

See Annotating generators and coroutines for details on using Generator in type annotations.

Added in version 3.5.

class collections.abc.Sequence
class collections.abc.MutableSequence

ABC para solo lectura y mutable secuencias.

Implementation note: Some of the mixin methods, such as __iter__(), __reversed__() and index(), make repeated calls to the underlying __getitem__() method. Consequently, if __getitem__() is implemented with constant access speed, the mixin methods will have linear performance; however, if the underlying method is linear (as it would be with a linked list), the mixins will have quadratic performance and will likely need to be overridden.

Distinto en la versión 3.5: El método index() agregó soporte para los argumentos stop y start.

class collections.abc.Set
class collections.abc.MutableSet

ABCs for read-only and mutable sets.

class collections.abc.Mapping
class collections.abc.MutableMapping

ABC para solo lectura y mutable mapeos.

class collections.abc.MappingView
class collections.abc.ItemsView
class collections.abc.KeysView
class collections.abc.ValuesView

ABC para mapeo, elementos, claves y valores vistas.

class collections.abc.Awaitable

ABC for awaitable objects, which can be used in await expressions. Custom implementations must provide the __await__() method.

Coroutine objetos e instancias de la clase Coroutine ABC son todas las instancias de este ABC.

Nota

In CPython, generator-based coroutines (generators decorated with @types.coroutine) are awaitables, even though they do not have an __await__() method. Using isinstance(gencoro, Awaitable) for them will return False. Use inspect.isawaitable() to detect them.

Added in version 3.5.

class collections.abc.Coroutine

ABC for coroutine compatible classes. These implement the following methods, defined in Objetos de corrutina: send(), throw(), and close(). Custom implementations must also implement __await__(). All Coroutine instances are also instances of Awaitable.

Nota

In CPython, generator-based coroutines (generators decorated with @types.coroutine) are awaitables, even though they do not have an __await__() method. Using isinstance(gencoro, Coroutine) for them will return False. Use inspect.isawaitable() to detect them.

See Annotating generators and coroutines for details on using Coroutine in type annotations. The variance and order of type parameters correspond to those of Generator.

Added in version 3.5.

class collections.abc.AsyncIterable

ABC for classes that provide an __aiter__ method. See also the definition of asynchronous iterable.

Added in version 3.5.

class collections.abc.AsyncIterator

ABC para clases que proveen métodos __aiter__ and __anext__. Ver también la definición de asynchronous iterator.

Added in version 3.5.

class collections.abc.AsyncGenerator

ABC for asynchronous generator classes that implement the protocol defined in PEP 525 and PEP 492.

See Annotating generators and coroutines for details on using AsyncGenerator in type annotations.

Added in version 3.6.

class collections.abc.Buffer

ABC para clases que proveen el método __buffer__(), implementando el protocolo búfer. Ver PEP 688.

Added in version 3.12.

Ejemplos y Recetas

Los ABC nos permiten preguntar a las clases o instancias si brindan una funcionalidad particular, por ejemplo:

size = None
if isinstance(myvar, collections.abc.Sized):
    size = len(myvar)

Several of the ABCs are also useful as mixins that make it easier to develop classes supporting container APIs. For example, to write a class supporting the full Set API, it is only necessary to supply the three underlying abstract methods: __contains__(), __iter__(), and __len__(). The ABC supplies the remaining methods such as __and__() and isdisjoint():

class ListBasedSet(collections.abc.Set):
    ''' Alternate set implementation favoring space over speed
        and not requiring the set elements to be hashable. '''
    def __init__(self, iterable):
        self.elements = lst = []
        for value in iterable:
            if value not in lst:
                lst.append(value)

    def __iter__(self):
        return iter(self.elements)

    def __contains__(self, value):
        return value in self.elements

    def __len__(self):
        return len(self.elements)

s1 = ListBasedSet('abcdef')
s2 = ListBasedSet('defghi')
overlap = s1 & s2            # The __and__() method is supported automatically

Notas sobre el uso de Set y MutableSet como un mixin:

  1. Since some set operations create new sets, the default mixin methods need a way to create new instances from an iterable. The class constructor is assumed to have a signature in the form ClassName(iterable). That assumption is factored-out to an internal classmethod called _from_iterable() which calls cls(iterable) to produce a new set. If the Set mixin is being used in a class with a different constructor signature, you will need to override _from_iterable() with a classmethod or regular method that can construct new instances from an iterable argument.

  2. To override the comparisons (presumably for speed, as the semantics are fixed), redefine __le__() and __ge__(), then the other operations will automatically follow suit.

  3. The Set mixin provides a _hash() method to compute a hash value for the set; however, __hash__() is not defined because not all sets are hashable or immutable. To add set hashability using mixins, inherit from both Set() and Hashable(), then define __hash__ = Set._hash.

Ver también