Chain-calling parent initialisers in python


Question

Consider this - a base class A, class B inheriting from A, class C inheriting from B. What is a generic way to call a parent class initialiser in an initialiser? If this still sounds too vague, here's some code.

class A(object):
    def __init__(self):
        print "Initialiser A was called"

class B(A):
    def __init__(self):
        super(B,self).__init__()
        print "Initialiser B was called"

class C(B):
    def __init__(self):
        super(C,self).__init__()
        print "Initialiser C was called"

c = C()

This is how I do it now. But it still seems a bit too non-generic - you still must pass a correct type by hand.

Now, I've tried using self.__class__ as a first argument to super(), but, obviously it doesn't work - if you put it in the initialiser for C - fair enough, B's initialiser gets called. If you do the same in B, "self" still points to an instance of C so you end up calling B's initialiser again (this ends in an infinite recursion).

There is no need to think about diamond inheritance for now, I am just interested in solving this specific problem.

1
276
5/16/2019 1:30:54 AM

Accepted Answer

The way you are doing it is indeed the recommended one (for Python 2.x).

The issue of whether the class is passed explicitly to super is a matter of style rather than functionality. Passing the class to super fits in with Python's philosophy of "explicit is better than implicit".

164
5/24/2009 4:12:27 PM

Python 3 includes an improved super() which allows use like this:

super().__init__(args)

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