"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

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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", | "contains", | |

| | "Container" | "iter", "len" | |#

| "Sequence" | "Reversible", | "getitem", | "contains", "iter", "reversed", "index", |

| | "Collection" | "len" | and "count" |#

| "MutableSequence" | "Sequence" | "getitem", | Inherited "Sequence" methods and "append", "clear", | | | | "setitem", | "reverse", "extend", "pop", "remove", and "iadd" | | | | "delitem", | |

| | | "len", "insert" | |#

| "ByteString" | "Sequence" | "getitem", | Métodos heredados "Sequence" |

| | | "len" | |#

| "Set" | "Collection" | "contains", | "le", "lt", "eq", "ne", "gt", | | | | "iter", "len" | "ge", "and", "or", "sub", |

| | | | "rsub", "xor", "rxor" and "isdisjoint" |#

| "MutableSet" | "Set" | "contains", | Métodos heredados "Set" y "clear", "pop", "remove", | | | | "iter", "len", | "ior", "iand", "ixor", and "isub" |

| | | "add", "discard" | |#

| "Mapping" | "Collection" | "getitem", | "contains", "keys", "items", "values", "get", |

| | | "iter", "len" | "eq", and "ne" |#

| "MutableMapping" | "Mapping" | "getitem", | Métodos heredados "Mapping" y "pop", "popitem", | | | | "setitem", | "clear", "update", and "setdefault" | | | | "delitem", | |

| | | "iter", "len" | |#

| "MappingView" | "Sized" | | "init", "len" and "repr" |#

| "ItemsView" | "MappingView", "Set" | | "contains", "iter" |#

| "KeysView" | "MappingView", "Set" | | "contains", "iter" |#

| "ValuesView" | "MappingView", | | "contains", "iter" |

| | "Collection" | | |#

| "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 ]-

[1] These ABCs override "subclasshook()" to support testing an interface by verifying the required methods are present and have not been set to "None". This only works for simple interfaces. More complex interfaces require registration or direct subclassing.

[2] 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)".

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 Anotación de generadores y corrutinas for details on using "Generator" in type annotations.

Added in version 3.5.

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

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.

index(value, start=0, stop=None)

  Return first index of *value*.

  Raises "ValueError" if the value is not present.

  Supporting the *start* and *stop* arguments is optional, but
  recommended.

  Distinto en la versión 3.5: The "index()" method gained support
  for the *stop* and *start* arguments.

Deprecated since version 3.12, will be removed in version 3.17: The "ByteString" ABC has been deprecated.Use "isinstance(obj, collections.abc.Buffer)" to test if "obj" implements the buffer protocol at runtime. For use in type annotations, either use "Buffer" or a union that explicitly specifies the types your code supports (e.g., "bytes | bytearray | memoryview")."ByteString" was originally intended to be an abstract class that would serve as a supertype of both "bytes" and "bytearray". However, since the ABC never had any methods, knowing that an object was an instance of "ByteString" never actually told you anything useful about the object. Other common buffer types such as "memoryview" were also never understood as subtypes of "ByteString" (either at runtime or by static type checkers).See PEP 688 for more details.

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 Anotación de generadores y corrutinas 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 Anotación de generadores y corrutinas 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:

• OrderedSet receta para un ejemplo basado en "MutableSet".

• Para obtener más información sobre ABCs, ver el módulo "abc" y PEP 3119.