def add(x, y):
    return x+y

class A():
    x = add(3,4)


    def p(self):
        print(self.x)


class B(A):
    pass




class Dog:
    tricks = [] # mistaken use of a class variable
    def __init__(self, name):
        self.name = name
    def add_trick(self, trick):
        self.tricks.append(trick)