gistfile1.py

class Base(object):
    things = []

    def update(self):
        print "I do nothing"

class A(Base):
    def update(self):
        self.things.append('This is A')

class B(Base):
    def update(self):
        self.things.append('This is B')

a = A()
b = B()

a.update()
a.update()
a.update()
a.update()
a.update()

print "A things are: %s" % a.things
print "B thigs are: %s" % b.things

"""
OUTPUT

python2.7 wtf.py
A things are: ['This is A', 'This is A', 'This is A', 'This is A', 'This is A']
B thigs are: ['This is A', 'This is A', 'This is A', 'This is A', 'This is A'

Why does B have things??

"""