class A:
   def g(self, n):
      return n
      
   def f(self, n):
      return self.g(n)
      
class B(A):
   def g(self, n):
      return 2 * n

a = A()
b = B()
print("a.f(1): {}".format(a.f(6)))
print("b.f(1): {}".format(b.f(6)))