Avoid specifying all arguments in a subclass

Question

I have a class:

class A(object):
    def __init__(self,a,b,c,d,e,f,g,...........,x,y,z)
        #do some init stuff

And I have a subclass w

Answer 1

Edit: based on Matt's suggestion, and to address gnibbler's concern re a positional-argument approach; you might check to make sure that the additional subclass-specific argument is being specified—similar to Alex's answer:

class B(A):
  def __init__(self, *args, **kwargs):
    try:
      self._w = kwargs.pop('w')
    except KeyError:
      pass
    super(B,self).__init__(*args, **kwargs)

>>> b = B(1,2,w=3)
>>> b.a
1
>>> b.b
2
>>> b._w
3

Original answer:
Same idea as Matt's answer, using super() instead.

Use super() to call superclass's __init__() method, then continue initialising the subclass:

class A(object):
  def __init__(self, a, b):
    self.a = a
    self.b = b

class B(A):
  def __init__(self, w, *args):
    super(B,self).__init__(*args)
    self.w = w