derivation.py

class A:
    def __init__(self, name):
        self.name = name

    def doit(self):
        print(self.name + " doit by class A")

    def dodo(self):
        self.doit()

class B(A):
    def doit(self):
        print(self.name + " doit by class B")


instance_a = A("a")
instance_b = B("b")

instance_a.dodo()
instance_b.dodo()

# > python derivation.py
# a doit by class A
# b doit by class B