Multiple Inheritance Ambiguity in Python

Question

Diamond Problem

class A():
   def method(self):
       print ("I am from class A")

class B(A):
   def method(self):
       print("I am from B")
       super().method()

class C(A):
   def method(self):
       print ("I am from class C")

class D(B,C):
   def method(self):
       print ("I am from class D")
       super().method()




d = D()

d.method()

I want to get the output as :

I am from class D
I am from B
I am from class A

However, i get the output as:

I am from class D
I am from B
I am from class C

How do i call method the method of A class using instance of D class? Is MRO a possible solution to this?

@MikeMüller Agree, I am Able to do this without multiple inheritance however i am more interested in understanding the underlying MRO, which is sending control of Program to C class instead of A. — Devesh G
– Devesh G, Commented Dec 12, 2017 at 12:03

Norrius · Accepted Answer · 2017-12-12 12:34:31Z

2

In Python 3 children always come in MRO before parents, this is needed to allow overrides work sensibly:

>>> D.__mro__
(<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.A'>, <class 'object'>)

In multiple inheritance, super() does not simply refer to the parent, it is used to get the next class in MRO. If you know what method of what class you want to call, do it directly:

class D(B,C):
   def method(self):
       print("I am from class D")
       A.method(self)

answered Dec 12, 2017 at 12:34

Norrius

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Suraj Rao · Accepted Answer · 2022-10-29 14:44:21Z

0

class A():
   def method(self):
       print ("I am from class A")

class B(A):
   def method(self):
       print("I am from B")
       A.method(self)

class C(A):
   def method(self):
       print ("I am from class C")

class D(B,C):
   def method(self):
       print ("I am from class D")
       super().method()




d = D()

d.method()

edited Oct 29, 2022 at 14:44

Suraj Rao

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answered Oct 29, 2022 at 14:38

Pranjali Modi

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