Python 中的 __hash___def hash(self, x)

官方文档对 可哈希的解释：hashable

An object is hashable if it has a hash value which never changes during its lifetime (it needs a hash() method), and can be compared to other objects (it needs an eq() method). Hashable objects which compare equal must have the same hash value.
Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.
Most of Python’s immutable built-in objects are hashable; mutable containers (such as lists or dictionaries) are not; immutable containers (such as tuples and frozensets) are only hashable if their elements are hashable. Objects which are instances of user-defined classes are hashable by default. They all compare unequal (except with themselves), and their hash value is derived from their id().

若对象在其生命周期内保持不变，而且能与其他对象相比较，那么这个对象是可哈希的。

通过__hash__返回一个int值，用来标记这个对象。对于类而言，如果没有实现 __eq__ 和 __hash__ 函数，那么会自动继承object.__hash__

   def __hash__(self):
        return hash(id(self))
    def __eq__(self, other):
        if isinstance(other, self.__class__):
            return hash(id(self))==hash(id(other))
        
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