python multiple inheritance passing arguments to constructors using super

Question

Consider the following snippet of python code

class A(object):     def __init__(self, a):         self.a = a  class B(A):     def __init__(self, a, b):         super(B, self).__init__(a)         self.b = b  class C(A):     def __init__(self, a, c):         super(C, self).__init__(a)         self.c = c  class D(B, C):     def __init__(self, a, b, c, d):         #super(D,self).__init__(a, b, c) ???         self.d = d 

I am wondering how can I pass a, b and c to corresponding base classes' constructors.

Answer 1

Well, when dealing with multiple inheritance in general, your base classes (unfortunately) should be designed for multiple inheritance. Classes B and C in your example aren't, and thus you couldn't find a proper way to apply super in D.

One of the common ways of designing your base classes for multiple inheritance, is for the middle-level base classes to accept extra args in their __init__ method, which they are not intending to use, and pass them along to their super call.

Here's one way to do it in python:

class A(object):     def __init__(self,a):         self.a=a  class B(A):     def __init__(self,b,**kw):         self.b=b         super(B,self).__init__(**kw)   class C(A):     def __init__(self,c,**kw):         self.c=c         super(C,self).__init__(**kw)  class D(B,C):     def __init__(self,a,b,c,d):         super(D,self).__init__(a=a,b=b,c=c)         self.d=d 

This can be viewed as disappointing, but that's just the way it is.