super.py

class Base(object):

  def foo(self):
    return "foo"

class FaultyClass(Base):

  def foo(self):
    return "faulty-" + Base.foo(self)

class CorrectClass(Base):

  def foo(self):
    return "correnct-" + super(CorrectClass, self).foo()

class UppercaseMixin(Base):

  def foo(self):
    return super(UppercaseMixin, self).foo().upper()

class SubclassFAIL(FaultyClass, UppercaseMixin):
    pass

class SubclassOK(CorrectClass, UppercaseMixin):
    pass


print SubclassFAIL().foo() # faulty-foo
print SubclassOK().foo() # correct-FOO
~