class PenguinPen: 
   def __init__(self):
      self.penguinCount = 0 

   def add (self, number = 1):
      """ Add one or more penguins to the pen The default number of penguins to add is 1 """
      self.penguinCount = self.penguinCount + number 
   
   def remove (self, number = 1): 
      """ Remove one or more penguins from the pen """ 
      self.penguinCount = self.penguinCount - number 

   def population (self): 
      """ How many penguins in the pen? """ 
      return self.penguinCount

penguinPen = PenguinPen()
penguinPen.add(5) # Tux y su familia
print penguinPen.population()