class Animal:

    def __init__(self, name):    # Constructor of the class

        self.name = name

    def talk(self):              # Abstract method, defined by convention only

        raise NotImplementedError("Subclass must implement abstract method")

class Cat(Animal):

    def talk(self):

        return 'Meow!'

class Dog(Animal):

    def talk(self):

        return 'Woof! Woof!'

animals = [Cat('Missy'),

           Cat('Mr. Mistoffelees'),

           Dog('Lassie')]

for animal in animals:

    print animal.name + ': ' + animal.talk()

# prints the following:

#

# Missy: Meow!

# Mr. Mistoffelees: Meow!

# Lassie: Woof! Woof!