python - 如何让 python 数据类继承 __hash__？

Question

以下将起作用，但我宁愿不需要重复 __hash__在每个子类中。有没有办法告诉数据类继承哈希函数(即不将其设置为 None )？

from dataclasses import dataclass


@dataclass
class Hashable:

    def __hash__(self):
        hashed = hash((
            getattr(self, key)
            for key in self.__annotations__
            ))
        return hashed


@dataclass
class Node(Hashable):
    name: str = 'Undefined'

    def __hash__(self):
        return Hashable.__hash__(self)

Answer 1

你的原因__hash__正在设置为 None是dataclasses试图阻止你用脚射击自己。你的第二堂课有 eq=True用于数据类装饰器(这是默认值)。从文档:

Here are the rules governing implicit creation of a __hash__() method. Note that you cannot both have an explicit __hash__() method in your dataclass and set unsafe_hash=True; this will result in a TypeError.

If eq and frozen are both true, by default dataclass() will generate a __hash__() method for you. If eq is true and frozen is false, __hash__() will be set to None, marking it unhashable (which it is, since it is mutable). If eq is false, __hash__() will be left untouched meaning the __hash__() method of the superclass will be used (if the superclass is object, this means it will fall back to id-based hashing).

所以只要通过 eq=False :

In [1]: from dataclasses import dataclass
   ...:
   ...:
   ...: @dataclass
   ...: class Hashable:
   ...:
   ...:     def __hash__(self):
   ...:         hashed = hash((
   ...:             getattr(self, key)
   ...:             for key in self.__annotations__
   ...:             ))
   ...:         return hashed
   ...:
   ...:
   ...: @dataclass(eq=False)
   ...: class Node(Hashable):
   ...:     name: str = 'Undefined'
   ...:

In [2]: hash(Node())
Out[2]: -9223372036579626267

但是，正如评论中指出的那样，这不是很安全，因为您有一个可变对象，现在可以进行哈希处理，并且与 __eq__ 的实现不一致。 ，它继承自 Hashable