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
Esse módulo fornece classes base abstratas que podem ser usadas para testar se uma classe fornece uma interface específica; por exemplo, se é hasheável ou se é um mapeamento.
Um teste issubclass()
ou isinstance()
para uma interface funciona em uma das três 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): # Herança direta
def __init__(self): ... # Método extra não exigido pela ABC
def __getitem__(self, index): ... # Método abstrato exigido
def __len__(self): ... # Método abstrato exigido
def count(self, value): ... # Opcionalmente substitui um método mixin
>>> 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: # Sem herança
def __init__(self): ... # Método extra exigido pela ABC
def __getitem__(self, index): ... # Método abstrato
def __len__(self): ... # Método abstrato
def count(self, value): ... # Método mixin
def index(self, value): ... # Método mixin
Sequence.register(D) # Registra ao invés de herdar
>>> 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:
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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.Callable¶
ABC for classes that provide the
__call__()
method.See Anotações de objetos chamáveis 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 asIterable
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 calliter(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()
andclose()
methods.See Anotando geradores e corrotinas for details on using
Generator
in type annotations.Adicionado na versão 3.5.
- class collections.abc.Sequence¶
- class collections.abc.MutableSequence¶
ABCs para sequências somente de leitura e mutáveis.
Implementation note: Some of the mixin methods, such as
__iter__()
,__reversed__()
andindex()
, 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.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. Usingisinstance(gencoro, Awaitable)
for them will returnFalse
. Useinspect.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()
, andclose()
. Custom implementations must also implement__await__()
. AllCoroutine
instances are also instances ofAwaitable
.Nota
In CPython, generator-based coroutines (generators decorated with
@types.coroutine
) are awaitables, even though they do not have an__await__()
method. Usingisinstance(gencoro, Coroutine)
for them will returnFalse
. Useinspect.isawaitable()
to detect them.See Anotando geradores e corrotinas for details on using
Coroutine
in type annotations. The variance and order of type parameters correspond to those ofGenerator
.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.
See Anotando geradores e corrotinas for details on using
AsyncGenerator
in type annotations.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:
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 internalclassmethod
called_from_iterable()
which callscls(iterable)
to produce a new set. If theSet
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.To override the comparisons (presumably for speed, as the semantics are fixed), redefine
__le__()
and__ge__()
, then the other operations will automatically follow suit.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 bothSet()
andHashable()
, 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.