An OOP example of Old McDonanld Had a Farm

farm.py

class Farm:
    def __init__(self):
        self.animals = []

    def add(self, animal):
        self.animals.append(animal)

    def __str__(self):
        s = ''
        for animal in self.animals:
            s += 'Old MacDonald had a farm, EE-I-EE-I-O,\n'       
            s += 'And on that farm he had a ' + animal.name + ', EE-I-EE-I-O,\n'
            s += 'With a ' + animal.noise * 2 + ' here and a '  + animal.noise * 2 +' there\n'
            s += 'Here a ' + animal.noise + ', there a ' + animal.noise + ', everywhere a '+ animal.noise * 2 + '\n'
        s += 'Old MacDonald had a farm, EE-I-EE-I-O.\n'
        return s

class Animal:
    def __init__(self, name, noise):
        self.name = name
        self.noise = noise


farm = Farm()
farm.add(Animal('cow', 'moo'))
print farm
farm.add(Animal('duck', 'kwak'))
farm.add(Animal('dog', 'woof'))
farm.add(Animal('cat', 'miaoo'))
print farm