python多态

class Animal:
    def run():
        print("animal is running")
class Dog(Animal):
    def run():
        print("dog is running")
class cat(Animal):
    def run():
        print("cat is running")        
def run(animal):
    animal.run()
-----------------------
animal = Animal()    
run(animal)
dog = Dog()
run(dog)
-----------------------
animal is running
dog is running