User Defined Classes are Hashable


Imad Dabbura


September 10, 2022

All user defined classes are hashable by defualt becuase they inherit __hash__ from object, which is related to their id(). This guarantees that different instances have different hashes since they have different id(). Therefore, hash(id(object)) == id(object) which is different for different objects.

class A:

a1 = A()
a2 = A()
id(a1) == hash(id(a1)) #=> True
id(a2) == hash(id(a2)) #=> True

If a user-defined class implements __eq__, then it needs to implement __hash__ and has to guarantee that it is hashable if all its attributes are hashable and if a == b then hash(a) == hash(b).