# `collections.abc` — Classes Base Abstratas para Contêineres

Adicionado 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`.

Adicionado 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__`
`Buffer` [1] |  | `__buffer__` |

Notas de rodapé

[1] (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)

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)`.

## 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.

  Adicionado 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.

  Adicionado 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.

  Adicionado 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.

  Descontinuado desde a versão 3.12, será removido na versão 3.14: The `ByteString` ABC has been deprecated. For use in typing, prefer a union, like `bytes | bytearray`, or `collections.abc.Buffer`. For use as an ABC, prefer `Sequence` or `collections.abc.Buffer`.

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.

  Adicionado 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.

  Adicionado na versão 3.5.

class collections.abc.AsyncIterable

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

  Adicionado 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.

  Adicionado na versão 3.5.

class collections.abc.AsyncGenerator

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

  Adicionado na versão 3.6.

class collections.abc.Buffer

  ABC for classes that provide the `__buffer__()` method, implementing the buffer protocol. See PEP 688.

  Adicionado na versão 3.12.

## 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

- OrderedSet receita para um exemplo baseado em `MutableSet`.

- Para mais informações sobre ABCs, consulte o módulo `abc` e PEP 3119.