Python set add same hash value item if no eq

example.py

class A:
    def __init__(self, val):
        self.val = val

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

    def __str__(self):
        return str(self.val)

    def __repr__(self):
        return str(self)


class B:
    def __init__(self, val):
        self.val = val

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

    def __eq__(self, other):  # important!
        return isinstance(other, self.__class__) and self.val == other.val

    def __str__(self):
        return str(self.val)

    def __repr__(self):
        return str(self)


a1 = A(42)
a2 = A(42)
print({a1, a2})
# {42, 42}


b1 = B(52)
b2 = B(52)
print({b1, b2})
# {52}