test.py

class A():
    def __init__(self):
        self._things = {
                'thing_one': 10,
                'thing_two': 10,
        }

    def get_thing(self, key):
        return self._things[key]

    def things(self):
        return self._things.keys()

class B(A):

    def __init__(self):
        self._things = {
                'thing_one': 20,
                'thing_two': 10,
        }


a = A()
b = B()

print 'All the things', a.things()

print 'A.thing_one', a.get_thing('thing_one')
print 'A.thing_two', a.get_thing('thing_two')

print 'B.thing_one', b.get_thing('thing_one')
print 'B.thing_two', b.get_thing('thing_two')

print 'B.thing_two', b.get_thing('thing_two')