collections.abc --- 容器的抽象基底類別

在 3.3 版被加入: 過去此模組是 collections 模組的一部分。

原始碼：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.

在 3.9 版被加入: These abstract classes now support []. See 泛型別名型別 and PEP 585.

Collections Abstract Base Classes

The collections module offers the following ABCs:

ABC

Inherits from

抽象方法

Mixin Methods

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 和 count

MutableSequence

Sequence

__getitem__、__setitem__、__delitem__、__len__、insert

繼承 Sequence 方法和 append、clear、reverse、extend、pop、remove 和 __iadd__

ByteString

Sequence

__getitem__、__len__

Sequence 的繼承方法

Set

Collection

__contains__、__iter__、__len__

__le__、__lt__、__eq__、__ne__、__gt__、__ge__、__and__、__or__、__sub__、__rsub__、__xor__、__rxor__ 和 isdisjoint

MutableSet

Set

__contains__、__iter__、__len__、add、discard

Inherited Set methods and clear, pop, remove, __ior__, __iand__, __ixor__, and __isub__

Mapping

Collection

__getitem__、__iter__、__len__

__contains__、keys、items、values、get、__eq__ 和 __ne__

MutableMapping

Mapping

__getitem__、__setitem__、__delitem__、__iter__、__len__

Inherited Mapping methods and pop, popitem, clear, update, and setdefault

MappingView

Sized

__init__、__len__ 和 __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__

註腳

集合抽象基底類別的詳細描述

class collections.abc.Container

有提供 __contains__() 方法之類別的 ABC。

class collections.abc.Hashable

有提供 __hash__() 方法之類別的 ABC。

class collections.abc.Sized

有提供 __len__() 方法之類別的 ABC。

class collections.abc.Callable

有提供 __call__() 方法之類別的 ABC。

See 註釋 callable 物件 for details on how to use Callable in type annotations.

class collections.abc.Iterable

有提供 __iter__() 方法之類別的 ABC。

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 for sized iterable container classes.

在 3.6 版被加入.

class collections.abc.Iterator

有提供 __iter__() 和 __next__() 方法之類別的 ABC。另請參閱 iterator 的定義。

class collections.abc.Reversible

亦有提供 __reversed__() 方法之可疊代類別的 ABC。

在 3.6 版被加入.

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.

在 3.5 版被加入.

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

唯讀且可變序列的 ABC。

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)

回傳 value 的第一個索引。

如果找不到該值，則引發 ValueError。

建議要支援 start 和 stop 引數，但並非必要。

在 3.5 版的變更: The index() method gained support for the stop and start arguments.

Deprecated since version 3.12, will be removed in version 3.17: ByteString ABC 已被棄用。

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 最初被設計為一個抽象類別，以作為 bytes 和 bytearray 的超型別 (supertype)。然而由於 ABC 從未擁有任何方法，知道一個物件是 ByteString 的實例從未真正告訴你任何關於該物件的有用資訊。其他常見的緩衝區型別如 memoryview 也從未被理解為 ByteString 的子型別（無論是在 runtime 還是由靜態型別檢查器）。

更多詳細資訊請參閱 PEP 688。

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

唯讀且可變集合的 ABC。

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

唯讀且可變對映的 ABC。

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

ABCs for mapping, items, keys, and values views.

class collections.abc.Awaitable

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

Coroutine objects and instances of the Coroutine ABC are all instances of this ABC.

備註

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.

在 3.5 版被加入.

class collections.abc.Coroutine

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

備註

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.

在 3.5 版被加入.

class collections.abc.AsyncIterable

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

在 3.5 版被加入.

class collections.abc.AsyncIterator

ABC for classes that provide __aiter__ and __anext__ methods. See also the definition of asynchronous iterator.

在 3.5 版被加入.

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.

在 3.6 版被加入.

class collections.abc.Buffer

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

在 3.12 版被加入.

Examples and Recipes

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

Notes on using Set and MutableSet as a 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.

也參考