super multiple parallel classes

[catlessness]

class a():
    def __init__(self):
        print('this is a')

class b():
    def __init__(self):
        print('this is b')

class c(a,b):
    def __init__(self):
        print('this is c')
        super().__init__()

inc=c()

I only get
'''
this is c
this is a
'''
this is b is skipped.
How do I fix this please? Thank you!

[Gribouillis]

When you call super().func(...), the first implementation of func() found in the ancestor classes according to the Method Resolution Order is executed. Other implementations are ignored. In your case, a.__init__() is found and b.__init__() is ignored.

You could call the method explicitly

class c(a,b):
    def __init__(self):
        print('this is c')
        super().__init__() # or a.__init__(self)
        b.__init__(self)

Multiple inheritance occurs rarely. When it occurs some classes are usually «mixin» classes and they don't have an __init__ method. So typically, "a" would be a mixin class without such a method and "b" would have an __init__ method, which would be called by super().__init__().

For user defined classes, it is customary to capitalize the class name, so use A, B, C...

[deanhystad]

It is important to remember that __init__() is just a method. Other than automatically getting called after an instance is created, it is no different than any other method. In you example __init__() is defined in both classes a and b. When c.__init__() calls super().__init__() which __init__ should it call? Both of them? If so, in what order?

A fix is to use super(). I mean really use super() instead of just partially. If you add super().__init__() to classes a and b, Python uses the MRO to resolve what methods in which order should be called.

class a():
    def __init__(self):
        print('this is a')
        super().__init__()
 
class b():
    def __init__(self):
        print('this is b')
        super().__init__()
 
class c(a,b):
    def __init__(self):
        print('this is c')
        super().__init__()

c()

Output:
this is c
this is a
this is b

This is the only problem I have with super(). If you use it in one place you really need to use it everywhere for it to work properly in all cases.