collections.abc — 容器抽象基类 ¶

3.3 版新增： 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 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__ ，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__(next): ...
					

>>> 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 .

3.9 版新增： 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 , 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__

脚注

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

These ABCs override object.__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.

3.6 版新增。

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。

3.6 版新增。

class collections.abc. 生成器 ¶

ABC for generator classes that implement the protocol defined in PEP 342 that extends iterators with the send() , throw() and close() methods. See also the definition of generator .

3.5 版新增。

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。

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.

3.5 版新增。

class collections.abc. Coroutine ¶

ABC for coroutine 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 。另请参阅定义对于 协程 .

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.

3.5 版新增。

class collections.abc. AsyncIterable ¶

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

3.5 版新增。

class collections.abc. AsyncIterator ¶

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

3.5 版新增。

class collections.abc. AsyncGenerator ¶

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

3.6 版新增。

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. 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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