CODEWITHSUNDEEP
python
proofit404
proofit404

Reputation: 386

In python why does super behave this way with multiple inheritance?

So we have a code snippet below. I don't understand why it behave this way. Why does super(B, self).go() resolves to the go method of the C class?

class A(object):
    def go(self):
        print("go A go!")

class B(A):
    def go(self):
        super(B, self).go()
        print("go B go!")

class C(A):
    def go(self):
        super(C, self).go()
        print("go C go!")

class D(B, C):
    def go(self):
        super(D, self).go()
        print("go D go!")

d = D()
d.go()
# go A go!
# go C go!
# go B go!
# go D go!

Upvotes: 0

Views: 95

Answers (1)

chepner
chepner

Reputation: 531315

Despite its name, super does not necessarily refer to a superclass. super(B, self) refers to the class in self's MRO that follows B.

You can see the MRO for D with

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

This means that from d.go, super(D, self) refers to B. When B.go is called as a result, super(B, self) refers to C, not A. This is because self is still an instance of D, so it is D.__mro__ that dictates what gets called next, not the static superclass of B.

The most important thing to remember about super is that inside Foo.go, you do not know what class super(Foo, self) will refer to, because you do not know if self is an instance of Foo or a descendent of Foo.

Upvotes: 5

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