Magic methods on class self

Question

I am looking for a way to call magic methods on class instances. In my case, I want to call hash on class based on properties. I found solution with metaclass, but I cannot access class properties from metaclass's method.

class X(type):
    @classmethod
    def __hash__(cls):
        return hash(cls.x)
class Y(metaclass=X):
        x = (1, 2, 3)
assert hash(Y) == hash((1, 2, 3))

I found just this thread: Defining magic methods on classes

"but I cannot access class properties from metaclass's method" - what? Sure you can. — user2357112, Aug 15 '17 at 18:21
Why do you want to override the hashing of class objects? You're now obliged to implement the `__eq__` too. — wim, Aug 15 '17 at 18:24

score 2 · Accepted Answer · answered Aug 15 '17 at 18:22

Take the @classmethod off.

class X(type):
    def __hash__(self):
        return hash(self.x)
class Y(metaclass=X):
        x = (1, 2, 3)
assert hash(Y) == hash((1, 2, 3))

You want __hash__ to receive Y, which is an instance of X. You don't want it to receive X.

Magic methods on class self

1 Answers1