dict 的 abc 继承关系

通过 collections 模块的抽象基类, 来理解 python 中 dict 的继承关系, 此处着重关注 Mapping 和 MutableMapping。

from collections.abc import Mapping, MutableMapping
__all__ = ["Awaitable", "Coroutine",
           "AsyncIterable", "AsyncIterator", "AsyncGenerator",
           "Hashable", "Iterable", "Iterator", "Generator", "Reversible",
           "Sized", "Container", "Callable", "Collection",
           "Set", "MutableSet",
           "Mapping", "MutableMapping",
           "MappingView", "KeysView", "ItemsView", "ValuesView",
           "Sequence", "MutableSequence",
           "ByteString",
           ]

dict 其实是属于MutableMapping, 它继承Mapping, Mapping继承Collection, 里面包括__len__,__iter__, __contains__, 所以dict和序列有很多接近的地方。

from collections.abc import Mapping, MutableMapping
#dict属于mapping类型

a = {}
print (isinstance(a, MutableMapping))
>>> True

注意

a是一个dict对象, 它并不是继承了MutableMapping, 而是实现了MutableMapping中的方法和魔法函数。源码中，是 MutableMapping.register(dict) 的方式实现的。