# zoo.py
#
# This example of class inheritence is inspired by perl's "perlboot",
# the "beginner's object oriented tutorial" by Randall Schwartz
# which can be seen at http://perldoc.perl.org/perlboot.html .
#
# First, here's what it does :
#
#   $ python zoo.py 
#   The dog says bow-wow.
#   The sheep says baaaa.
#   The cat says meow.
#   The dog says bow-wow.
#   The cat says meow.
#   The sheep says baaaa.
#
# Now, look at the classes, methods, and functions,
# and see how it all fits together.
#
# In particular:
#
#   Which classes are superclasses (or 'parent' class) ?
#   Which are subclasses (or 'child' class) ?
#   Which are contained as data within other classes?
#
#   What is the syntax for defining a subclass?
#
#   What is the syntax for calling a superclass from within a subclass method?
#
#   What is that "factory" function all about?  Is it in a class?

class Animal:
  """A generic Old-MacDonald-ish animal."""
  def __init__(self, name="animal"):
    """Initialize the animal with its name."""
    self.name = name
  def sound(self):
    """Return as a string the animal's sound."""
    return "hmmm"
  def speak(self):
    """Return a string like 'The AnimalName says ItsSound.'."""
    return "The %s says %s." % (self.name, self.sound())

class Cat(Animal):
  def __init__(self):
    Animal.__init__(self, 'cat')
  def sound(self):
    return "meow"

class Dog(Animal):
  def __init__(self):
    Animal.__init__(self, 'dog')
  def sound(self):
    return "bow-wow"

class Sheep(Animal):
  def __init__(self):
    Animal.__init__(self, 'sheep')
  def sound(self):
    return "baaaa"

class Farm:
  """A collection of animals."""
  def __init__(self):
    self.animals = []
  def add(self, animal, count=1):
    """Add an animal to the farm."""
    for i in range(count):
      self.animals.append(animal)
  def chorus(self):
    """Return string of animal speech."""
    speech = ""
    for animal in self.animals:
      speech += animal.speak() + "\n"
    return speech

def animal_factory(which):
  """Given a string like 'cat', return the corresponding animal."""
  if which == 'cat':
    return Cat()
  elif which == 'dog':
    return Dog()
  elif which == 'sheep':
    return Sheep()

def macdonald():
  """Create a farm with some animals, and print their chorus."""
  names = ['dog', 'sheep', 'cat', 'dog', 'cat', 'sheep']
  farm = Farm()
  for which in names:
    farm.add(animal_factory(which))
  print farm.chorus()

macdonald()