Python Call Parent Method Multiple Inheritance

Question

So, i have a situation like this.

class A(object):
    def foo(self, call_from):
        print "foo from A, call from %s" % call_from


class B(object):
    def foo(self, call_from):
        print "foo from B, call from %s" % call_from


class C(object):
    def foo(self, call_from):
        print "foo from C, call from %s" % call_from


class D(A, B, C):
    def foo(self):
        print "foo from D"
        super(D, self).foo("D")

d = D()
d.foo()

The result of the code is

foo from D
foo from A, call from D

I want to call all parent method, in this case, foo method, from D class without using super at the parent class like A. I just want to call the super from the D class. The A, B, and C class is just like mixin class and I want to call all foo method from D. How can i achieve this?

Answer 1

You can use __bases__ like this

class D(A, B, C):
    def foo(self):
        print("foo from D")
        for cls in D.__bases__:
            cls().foo("D")

With this change, the output will be

foo from D
foo from A, call from D
foo from B, call from D
foo from C, call from D

Answer 2

Add super() call's in other classes as well except C. Since D's MRO is

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

You don't need super call in C.

Code:

class A(object):
    def foo(self, call_from):
        print "foo from A, call from %s" % call_from
        super(A,self).foo('A')

class B(object):
    def foo(self, call_from):
        print "foo from B, call from %s" % call_from
        super(B, self).foo('B')


class C(object):
    def foo(self, call_from):
        print "foo from C, call from %s" % call_from

class D(A, B, C):
    def foo(self):
        print "foo from D"
        super(D, self).foo("D")

d = D()
d.foo()

Output:

foo from D
foo from A, call from D
foo from B, call from A
foo from C, call from B

Answer 3

I believe the call to super in sub-classes is the more Pythonic approach. One doesn't have to use the parent class names (particularly in super). Elaborating on the previous example, here's some code that should work (python 3.6+):

class A:
    def foo(self, call_from):
        print(f"foo from A, call from {call_from}")
        super().foo('A')

class B:
    def foo(self, call_from):
        print(f"foo from B, call from {call_from}")
        super().foo('B')


class C(object):
    def foo(self, call_from):
        print(f"foo from C, call from {call_from}")
        super().foo('C')

class StopFoo:
    def foo(self, call_from):
        pass

class D(A, B, C, StopFoo):
    def foo(self, call_from):
        print(f"foo from D, call from {call_from}")
        super().foo('D')

If you run this code:

d = D()
d.foo('D')

You will get:

foo from D, call from D
foo from A, call from D
foo from B, call from A
foo from C, call from B

The advantage of this strategy is you don't have to bother about the inheritance order, AS LONG as you include the StopFoo class. This one is a bit peculiar and might not be the best strategy to accomplish this task. Basically, every class in the inheritance tree calls the foo method and calls the parent method, which does the same. We might be talking about multiple inheritance, but an inheritance tree is actually flat (D -> A -> B -> C -> Stopfoo -> object). We can change the order of inheritance, add new classes to this pattern, remove them, just call one class... but the trick remains: include StopFoo before the call to foo leaves the class we have defined.

For a mixin pattern with hooks, this might make sense. But of course, the solution isn't that useful in every case either. Don't fear super though, it has many tricks and can be useful in simple and multiple inheritance, with mixins or simple abstract classes.