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  • collections.abc — 容器抽象基类
    • 集合抽象基类
    • Collections Abstract Base Classes – Detailed Descriptions
    • 范例和配方

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  9. collections.abc — 容器抽象基类

collections.abc — 容器抽象基类 ¶

Added in version 3.3: Formerly, this module was part of the collections 模块。

源代码： Lib/_collections_abc.py

本模块提供 抽象基类 that can be used to test whether a class provides a particular interface; for example, whether it is hashable or whether it is a 映射 .

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__ ，和 __reversed__ because the in-operator ， 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__ ，和 __iter__ is insufficient for distinguishing a Sequence 从 Mapping .

Added in version 3.9: These abstract classes now support [] 。见 一般别名类型 and PEP 585 .

集合抽象基类 ¶

The collections module offers the following ABCs :

ABC (抽象基类)

Inherits from

Abstract Methods

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

继承 Sequence methods and append , clear , reverse , extend , pop , remove ，和 __iadd__

ByteString

Sequence

__getitem__ , __len__

继承 Sequence 方法

Set

Collection

__contains__ , __iter__ , __len__

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

MutableSet

Set

__contains__ , __iter__ , __len__ , add , discard

继承 Set methods and clear , pop , remove , __ior__ , __iand__ , __ixor__ ，和 __isub__

Mapping

Collection

__getitem__ , __iter__ , __len__

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

MutableMapping

Mapping

__getitem__ , __setitem__ , __delitem__ , __iter__ , __len__

继承 Mapping methods and pop , popitem , clear , update ，和 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__

脚注

[ 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 是调用 iter(obj) .

Collections Abstract Base Classes – Detailed Descriptions ¶

class collections.abc. Container ¶

ABC for classes that provide the __contains__() 方法。

class collections.abc. Hashable ¶

ABC for classes that provide the __hash__() 方法。

class collections.abc. Sized ¶

ABC for classes that provide the __len__() 方法。

class collections.abc. 可调用 ¶

ABC for classes that provide the __call__() 方法。

class collections.abc. Iterable ¶

ABC for classes that provide the __iter__() 方法。

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 是调用 iter(obj) .

class collections.abc. Collection ¶

ABC for sized iterable container classes.

Added in version 3.6.

class collections.abc. Iterator ¶

ABC for classes that provide the __iter__() and __next__() methods. See also the definition of iterator .

class collections.abc. Reversible ¶

ABC for iterable classes that also provide the __reversed__() 方法。

Added in version 3.6.

class collections.abc. 生成器 ¶

ABC for generator classes that implement the protocol defined in PEP 342 that extends iterators 采用 send() , throw() and close() 方法。

Added in version 3.5.

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

ABCs for read-only and mutable sequences .

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.

3.5 版改变： The index() method added support for stop and start 自变量。

Deprecated since version 3.12, will be removed in version 3.14: The ByteString ABC has been deprecated. For use in typing, prefer a union, like bytes | bytearray ，或 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. 映射 ¶
class collections.abc. MutableMapping ¶

ABCs for read-only and mutable mappings .

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__() 方法。

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

注意

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 。使用 inspect.isawaitable() to detect them.

Added in version 3.5.

class collections.abc. Coroutine ¶

ABC for 协程 compatible classes. These implement the following methods, defined in 协程对象 : send() , throw() ，和 close() . Custom implementations must also implement __await__() . All Coroutine instances are also instances of Awaitable .

注意

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 。使用 inspect.isawaitable() to detect them.

Added in version 3.5.

class collections.abc. AsyncIterable ¶

ABC for classes that provide an __aiter__ method. See also the definition of 异步可迭代 .

Added in version 3.5.

class collections.abc. AsyncIterator ¶

ABC for classes that provide __aiter__ and __anext__ methods. See also the definition of 异步迭代器 .

Added in version 3.5.

class collections.abc. AsyncGenerator ¶

ABC for 异步生成器 classes that implement the protocol defined in PEP 525 and PEP 492 .

Added in version 3.6.

class collections.abc. 缓冲 ¶

ABC for classes that provide the __buffer__() method, implementing the 缓冲协议 。见 PEP 688 .

3.12 版添加。

范例和配方 ¶

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__() ，和 __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() 调用 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 .

另请参阅

  • OrderedSet recipe for an example built on MutableSet .

  • For more about ABCs, see the abc module and PEP 3119 .

内容表

  • collections.abc — 容器抽象基类
    • 集合抽象基类
    • Collections Abstract Base Classes – Detailed Descriptions
    • 范例和配方

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