class Mixin(object):
  def __init__(self, *args, **kwargs):
    super(Mixin, self).__init__(*args, **kwargs)
    print 'yelp!'

class Foo(Mixin):
  def __init__(self, *args, **kwargs):
    self.bla = kwargs.pop('bla')
    super(Foo, self).__init__(*args, **kwargs)

f = Foo(bla=42)
yelp!
f = Foo(bla=42, bar=23)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __init__
  File "<stdin>", line 3, in __init__
TypeError: object.__init__() takes no parameters