class Flying:
    def fly(self):
        print("I'm flying.")
    
    def land(self):
        print("I'm landing.")

class Swimming:
    def swim(self):
        print("I'm swimming.")
    
    def dive(self):
        print("I'm diving.")

class Duck(Flying, Swimming):
    pass

d = Duck()
d.fly()   # prints "I'm flying."
d.swim()  # prints "I'm swimming."