8.4. collections.abc — 容器抽象基类 ¶

8.4.1. Collections Abstract Base Classes ¶

The collections module offers the following ABCs :

class collections.abc. Container ¶

class collections.abc. Hashable ¶

class collections.abc. Sized ¶

class collections.abc. Callable ¶

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

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 is to call 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. Mapping ¶

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() or asyncio.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 . See also the definition of 协程 .

注意

In CPython, generator-based coroutines (generators decorated with types.coroutine() or asyncio.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。

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() which calls 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. 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 .