Walks like a duck...

duck.py

class Duck(object):
    def walk(self):
        print('waddle')

    def talk(self):
        print('quack')


class Donald(object):
    def walk(self):
        print('waddle')

    def talk(self):
        print('quack')


def do_ducky_things(duck: Duck):
    duck.walk()
    duck.talk()


donald = Donald()
do_ducky_things(donald)