Question

I’d like to do something like this:

class A(object):
    def __init__(self, **kwargs):
       """ 
       return exception if certain arguments not set
       """

class B(A):
    def __init__(self, **kwargs):
       super(B, self).__init__(**kwargs)

Basically, each subclass will require certain arguments to be properly instantiated. They are the same params across the board. I only want to do the checking of these arguments once. If I can do this from the parent init() – all the better.

Is it possible to do this?

Answer 1

Sure. This is not an uncommon pattern:

class A(object):
    def __init__(self, foo, bar=3):
        self.foo = foo
        self.bar = bar

class B(A):
    def __init__(self, quux=6, **kwargs):
        super(B, self).__init__(**kwargs)

        self.quux = quux

B(foo=1, quux=4)

This also insulates you a little from super shenanigans: now A‘s argspec can change without requiring any edits to B, and diamond inheritance is a little less likely to break.