multiple inheritance in python with super [duplicate]

Question

class Parent1(object):
    def foo(self):
        print "P1 foo"

    def bar(self):
        print "P1 bar"


class Parent2(object):
    def foo(self):
        print "P2 foo"

    def bar(self):
        print "P2 bar"



class Child(Parent1, Parent2):
    def foo(self):
        super(Parent1, self).foo()

    def bar(self):
        super(Parent2, self).bar()

c = Child() 
c.foo()
c.bar()

The intention is to inherit foo() from Parent1 and bar() from Parent2. But c.foo() resulting for parent2 and c.bar() is reulting error. Please point to the problem and provide solution.

The first argument to super is the class to start looking "above" in the inheritance hierarchy, so foo will be from Parent2 and bar will be from object (which has no such attribute, presumably causing the error you mention only in passing). Instead, use Child and Parent1 in your super calls. — jonrsharpe
– jonrsharpe, Commented May 9, 2016 at 7:54
@jonrsharpe : Thanks for clarification. the possible duplicate question you suggested has initialization function init . so, I was not sure that normal methods and init will follow the same rule for inheritance — SamCodes
– SamCodes, Commented May 9, 2016 at 8:31
All instance methods, __init__ and other "magic" methods included, follow the same rules. — jonrsharpe
– jonrsharpe, Commented May 9, 2016 at 8:55

Byte Commander · Accepted Answer · 2016-05-09 08:06:54Z

4

You could call the methods directly on the parent classes, providing the self argument manually. This should give you the highest level of control and be the easiest way to understand. From other points of view it might be suboptimal though.

Here's only the Child class, the rest of your code stays the same:

class Child(Parent1, Parent2):
    def foo(self):
        Parent1.foo(self)

    def bar(self):
        Parent2.bar(self)

Running your snippet with the described changes results in the desired output:

P1 foo
P2 bar

See this code running on ideone.com

answered May 9, 2016 at 8:06

Byte Commander

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2 Comments

SamCodes Over a year ago

We provide self to when we define a method to refer the object. But when we are calling the method from child class we are providing it manually. So How does it work?

Byte Commander Over a year ago

Inside the class MyClass, you may have a method defined like this def foo(self, arg1, arg2). When you run my_instance = MyClass(), you create a new instance of your class. Now you can call the method from the instance object like this: my_instance.foo("This is arg1", "This is arg2"). This way, the self parameter gets implicitly set to the instance object on which we call the method, i.e. here it would be my_instance. Now if we call the same method on a specific class, we have to provide the self argument explicitly: MyClass.foo(my_instance, "This is arg1", "This is arg2"). Ok?

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