Check if self is instance of subclass in python

Question

I have a class called A, with two subclasses B and C. Does the following make sense? Or is there a better way to it?

class A():
    ...

    def do_stuff(self):
        self.do_this()
        self.do_that()
        if isInstance(self, B):
            self.do_the_b_stuff()
        elif isInstance(self, C):
            self.do_the_c_stuff()

Aran-Fey · Accepted Answer · 2018-11-01 15:56:05Z

9

There's a better way to do it: Override do_stuff in the child classes.

class A:
    def do_stuff(self):
        self.do_this()
        self.do_that()

class B(A):
    def do_stuff(self):
        super().do_stuff()  # call the parent implementation
        self.do_the_b_stuff()

class C(A):
    def do_stuff(self):
        super().do_stuff()  # call the parent implementation
        self.do_the_c_stuff()

The advantage of this solution is that the base class doesn't have to know about its child classes - B and C aren't referenced anywhere in A's body. This makes it easier to add additional subclasses, should that ever be necessary.

answered Nov 1, 2018 at 15:56

Aran-Fey

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1 Comment

lukehawk Over a year ago

Thanks for the edit. I appreciate knowing why this is better, and that makes great sense. Thanks for the answer too!

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