bj's homework

gistfile1.py

>>> import math
>>> 
>>> 
>>> class Shape(object):
...     def area(self):
...         raise NotImplementedError("An arbitrary shape doesn't have a defined "
...                                   "area. Please use a descendent class.")
... 
>>> 
>>> class Circle(Shape):
...     def __init__(self, radius):
...         self.radius = radius
...     
...     def area(self):
...         return 2 * math.pi * self.radius
... 
>>> 
>>> class Rectangle(Shape):
...     def __init__(self, width, height):
...         self.width = width
...         self.height = height
...     
...     def area(self):
...         return self.width * self.height
... 
>>> 
>>> class Square(Rectangle):
...     def __init__(self, width):
...         super(Square, self).__init__(width, width)
... 
>>> 
>>> Circle(10).area()
62.83185307179586
>>> Rectangle(10,20).area()
200
>>> Square(10).area()
100
>>> Rectangle(10,10).area()
100
>>>