collections.abc
--- 容器的抽象基类¶
3.3 新版功能: 该模块曾是 collections
模块的组成部分。
该模块定义了一些 抽象基类,它们可用于判断一个具体类是否具有某一特定的接口;例如,这个类是否可哈希,或其是否为映射类。
容器抽象基类¶
这个容器模块提供了以下 ABCs:
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-
class
collections.abc.
Container
¶ -
class
collections.abc.
Hashable
¶ -
class
collections.abc.
Sized
¶ -
class
collections.abc.
Callable
¶ 分别提供了
__contains__()
,__hash__()
,__len__()
和__call__()
方法的抽象基类。
-
class
collections.abc.
Iterable
¶ 提供了
__iter__()
方法的抽象基类。使用
isinstance(obj, Iterable)
可以检测一个类是否已经注册到了Iterable
或者实现了__iter__()
函数,但是无法检测这个类是否能够使用__getitem__()
方法进行迭代。检测一个对象是否是 iterable 的唯一可信赖的方法是调用iter(obj)
。
-
class
collections.abc.
Collection
¶ 集合了 Sized 和 Iterable 类的抽象基类。
3.6 新版功能.
-
class
collections.abc.
Iterator
¶ 提供了
__iter__()
和__next__()
方法的抽象基类。参见 iterator 的定义。
-
class
collections.abc.
Reversible
¶ 为可迭代类提供了
__reversed__()
方法的抽象基类。3.6 新版功能.
-
class
collections.abc.
Generator
¶ 生成器类,实现了 PEP 342 中定义的协议,继承并扩展了迭代器,提供了
send()
,throw()
和close()
方法。参见 generator 的定义。3.5 新版功能.
-
class
collections.abc.
Sequence
¶ -
class
collections.abc.
MutableSequence
¶ -
class
collections.abc.
ByteString
¶ 只读且可变的序列 sequences 的抽象基类。
实现笔记:一些混入(Maxin)方法比如
__iter__()
,__reversed__()
和index()
会重复调用底层的__getitem__()
方法。因此,如果实现的__getitem__()
是常数级访问速度,那么相应的混入方法会有一个线性的表现;然而,如果底层方法是线性实现(例如链表),那么混入方法将会是平方级的表现,这也许就需要被重构了。在 3.5 版更改: index() 方法支持 stop 和 start 参数。
-
class
collections.abc.
MappingView
¶ -
class
collections.abc.
ItemsView
¶ -
class
collections.abc.
KeysView
¶ -
class
collections.abc.
ValuesView
¶ 映射及其键和值的视图 views 的抽象基类。
-
class
collections.abc.
Awaitable
¶ 为可等待对象 awaitable 提供的类,可以被用于
await
表达式中。习惯上必须实现__await__()
方法。协程对象 Coroutine 和
Coroutine
抽象基类的实例都是这个抽象基类的实例。注解
在 CPython 里,基于生成器的协程(使用
types.coroutine()
或asyncio.coroutine()
包装的生成器)都是 可等待对象,即使他们不含有__await__()
方法。使用isinstance(gencoro, Awaitable)
来检测他们会返回False
。要使用inspect.isawaitable()
来检测他们。3.5 新版功能.
-
class
collections.abc.
Coroutine
¶ ABC for coroutine compatible classes. These implement the following methods, defined in 协程对象:
send()
,throw()
, andclose()
. Custom implementations must also implement__await__()
. AllCoroutine
instances are also instances ofAwaitable
. See also the definition of coroutine.注解
In CPython, generator-based coroutines (generators decorated with
types.coroutine()
orasyncio.coroutine()
) are awaitables, even though they do not have an__await__()
method. Usingisinstance(gencoro, Coroutine)
for them will returnFalse
. Useinspect.isawaitable()
to detect them.3.5 新版功能.
-
class
collections.abc.
AsyncIterable
¶ ABC for classes that provide
__aiter__
method. See also the definition of asynchronous iterable.3.5 新版功能.
-
class
collections.abc.
AsyncIterator
¶ ABC for classes that provide
__aiter__
and__anext__
methods. See also the definition of asynchronous iterator.3.5 新版功能.
-
class
collections.abc.
AsyncGenerator
¶ ABC for asynchronous generator classes that implement the protocol defined in PEP 525 and PEP 492.
3.6 新版功能.
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__()
, 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:
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 callscls(iterable)
to produce a new set. If theSet
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.To override the comparisons (presumably for speed, as the semantics are fixed), redefine
__le__()
and__ge__()
, then the other operations will automatically follow suit.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 bothSet()
andHashable()
, then define__hash__ = Set._hash
.
参见
OrderedSet recipe for an example built on
MutableSet
.