继承-在子类中\uuuu散列\uuuuu设置为无

考虑:

class Comparable:
    def _key(self):
        raise NotImplementedError

    def __hash__(self):
        return hash(self._key())

    def __eq__(self, other):
        ...

    def __lt__(self, other):
        ...


class A(Comparable): pass

class B(A):
    def __str__(self):
        return "d"

    def __eq__(self, other):
        return isinstance(self, type(other))

    def _key(self):
        return str(self),

b = B()

很明显,人们会期望 b.__hash__ Comparable 哪一个 B 是的一个子类。

瞧,它被定义了,但计算结果是 None . 有什么好处?

>> b
<__main__.B object at 0x00000183C9734978>
>> '__hash__' in dir(b)
True
>> b.__hash__

>> b.__hash__ is None
True
>> B.__mro__
(<class '__main__.B'>, <class '__main__.A'>, <class '__main__.Comparable'>, <class 'object'>)
>> isinstance(b, Comparable)
True

__init__ super().__init__() 可比较的 和 A .