How To Define __hash__ When An Object Can Be Equal To Different Kind Of Objects?

In Python doscumentation, we can read about __hash__ function : The only required property is that objects which compare equal have the same hash value. I have an object which

Solution 1:

You can't define a consistent hash. First, your class does not define __eq__ consistently; it is not guaranteed that if x == y and y == z, then x == z. Second, your object is mutable. In Python, mutable objects are not supposed to be hashable.

If a class defines mutable objects and implements a __cmp__() or __eq__() method, it should not implement __hash__(), since hashable collection implementations require that a object’s hash value is immutable (if the object’s hash value changes, it will be in the wrong hash bucket).

Example of broken ==:

x = MyClass('foo')
y = 'foo'z = MyClass('foo')

x == y # Truey == z # Truex == z # False