Python Multiple Inheritance super().__init__()

Question

I have two classes, with the same parameter initialized by their __init__ method. I would like to inherit both classes in class "X". But I will get: TypeError: B.__init__() missing 1 required positional argument: 'my_param'

Reproducible Example:

class A:
    def __init__(self, my_param):
        super().__init__()
        self.my_param = my_param


class B:
    def __init__(self, my_param):
        super().__init__()
        self.my_param = my_param * 2


class X(A, B):
    def __init__(self, my_param):
        super().__init__(my_param=my_param)

a = X(my_param=1)
print(a.my_param)

A and B are Mixins, they provide additional functionality for Child Classes. They can be used separetly or together. Lets's say class A provides searhc functionality for search by ID, where class B provides search by value.

Is there a way to set my_param for each of A and B or to set it without getting the error?

Answer 1

This can't be done just using super() calls, because the superclass of the last class in the chain will be object, which doesn't take a my_param parameter.

See python multiple inheritance passing arguments to constructors using super for more discussion of parameter passing to __init__() methods with multiple inheritance.

So you need to change X to call the superclass init methods explicitly, rather than using super(). And A and B shouldn't call super().__init__() because they're subclasses of object, which doesn't do anything in its __init__().

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

class B:
    def __init__(self, my_param):
        self.my_param = my_param * 2

class X(A, B):
    def __init__(self, my_param):
        A.__init__(self, my_param=my_param)
        B.__init__(self, my_param=my_param)