8.4. 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.

8.4.1. Collections Abstract Base Classes ¶

The collections module offers the following ABCs :

ABC (抽象基类)	Inherits from	Abstract Methods	Mixin Methods
Container		__contains__
Hashable		__hash__
Iterable		__iter__
Iterator	Iterable	__next__	__iter__
Sized		__len__
Callable		__call__
Sequence	Sized , Iterable , Container	__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__
Set	Sized , Iterable , Container	__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	Sized , Iterable , Container	__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 , and setdefault
MappingView	Sized		__len__
ItemsView	MappingView , Set		__contains__ , __iter__
KeysView	MappingView , Set		__contains__ , __iter__
ValuesView	MappingView		__contains__ , __iter__

class collections.abc. Container ¶

class collections.abc. Hashable ¶

class collections.abc. Sized ¶

class collections.abc. 可调用 ¶

ABCs for classes that provide respectively the methods __contains__() , __hash__() , __len__() ，和 __call__() .

class collections.abc. Iterable ¶

ABC for classes that provide the __iter__() method. See also the definition of iterable .

class collections.abc. 迭代器 ¶

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

class collections.abc. Sequence ¶

class collections.abc. MutableSequence ¶

ABCs for read-only and mutable sequences .

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 .

These 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. 若 Set mixin is being used in a class with a different constructor signature, you will need to override _from_iterable() with a classmethod 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 对于 example built on MutableSet .
• For more about ABCs, see the abc module and PEP 3119 .

内容表

• 8.4. collections.abc — 容器抽象基类
  • 8.4.1. Collections Abstract Base Classes

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