collections.abc — Classes Base Abstratas para Contêineres

Novo na versão 3.3: Anteriormente, esse módulo fazia parte do módulo collections.

Código-fonte: 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.

An issubclass() or isinstance() test for an interface works in one of three ways.

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

Complex interfaces do not support this last technique because an interface is more than just the presence of method names. Interfaces specify semantics and relationships between methods that cannot be inferred solely from the presence of specific method names. For example, knowing that a class supplies __getitem__, __len__, and __iter__ is insufficient for distinguishing a Sequence from a Mapping.

Novo na versão 3.9: These abstract classes now support []. See Tipo Generic Alias and PEP 585.

Classes Base Abstratas de Coleções

O módulo de coleções oferece o seguinte ABCs:

ABC

Herda de

Métodos Abstratos

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__

ByteString

Sequence

__getitem__, __len__

Herdado Sequence métodos

Set

Collection

__contains__, __iter__, __len__

__le__, __lt__, __eq__, __ne__, __gt__, __ge__, __and__, __or__, __sub__, __xor__, e isdisjoint

MutableSet

Set

__contains__, __iter__, __len__, add, discard

Herdado Set métodos e clear, pop, remove, __ior__, __iand__, __ixor__, e __isub__

Mapping

Collection

__getitem__, __iter__, __len__

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

MutableMapping

Mapping

__getitem__, __setitem__, __delitem__, __iter__, __len__

Herdado Mapping métodos e pop, popitem, clear, update, e setdefault

MappingView

Sized

__len__

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__

Notas de rodapé

Collections Abstract Base Classes – Detailed Descriptions

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.

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 classes de contêiner iterável de tamanho.

Novo na versão 3.6.

class collections.abc.Iterator

ABC para classes que fornecem os métodos __iter__() e métodos __next__(). Veja também a definição de iterator.

class collections.abc.Reversible

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

Novo na versão 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.

Novo na versão 3.5.

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

ABCs para sequências somente de leitura e mutáveis.

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.

Alterado na versão 3.5: O método index() adicionou suporte para os argumentos stop e start.

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

ABCs for read-only and mutable sets.

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

ABCs para somente leitura e mutável mappings.

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

ABCs para mapeamento, itens, chaves e valores views.

class collections.abc.Awaitable

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

Objetos e instâncias de corrotina da ABC Coroutine são todas instâncias dessa 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.

Novo na versão 3.5.

class collections.abc.Coroutine

ABC for coroutine compatible classes. These implement the following methods, defined in Objetos corrotina: 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.

Novo na versão 3.5.

class collections.abc.AsyncIterable

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

Novo na versão 3.5.

class collections.abc.AsyncIterator

ABC para classes que fornecem os métodos __aiter__ e __anext__. Veja também a definição de iterador assíncrono.

Novo na versão 3.5.

class collections.abc.AsyncGenerator

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

Novo na versão 3.6.

Exemplos e receitas

ABCs allow us to ask classes or instances if they provide particular functionality, for example:

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 o uso de Set e MutableSet como um 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 também