Assignment 11

Problems

1. Using a class does not necessarily make a program object oriented. Consider the code below. The first warning bells are that the class has no methods and the functions in the module are stand alone functions not class methods. The code uses a class, but if you look carefully you will see that the class is used to represent not one type of object but several types of objects. The give-away is the attribute kind and the way it is tested by the remaining functions in the module to decide what to do.

   # Suppose we need to support circles, equilateral triangles and squares.
   (CIRCLE, TRIANGLE, SQUARE) = range(3)
   class shape:
       def __init__(self, k, c, s):
           self.kind = k
           self.centre = c
           self.size = s
   ...
   def draw(shape):
       if shape.kind == CIRCLE:
           # code to draw a circle
           ...
       elif shape.kind == TRIANGLE:
           # code to draw a triangle
           ...
       else:
           # code to draw a square
           ...
   def fill(shape, colour):
       # Fills the shape with colour.
       if shape.kind == CIRCLE:
           # code to fill in a circle
           ...
       elif shape.kind == TRIANGLE:
           # code to fill in a triangle
           ...
       else:
           # code to fill in a square
           ...
   def rotate(shape, angle):
       # Rotates the shape about its centre by angle.
       if shape.kind == CIRCLE:
           # code to rotate a circle (hint: do nothing)
           ...
       elif shape.kind == TRIANGLE:
           # code to rotate a triangle
           ...
       else:
           # code to rotate a square
           ...
    
   def groovy(shape_list):
       for shape in shape_list:
           draw(shape)
           rotate(shape, math.pi/2)
           fill(shape, random.randint(0,15))

   1. Suppose you are given this code and told you must add support for an additional shape, pentagons. What changes would you have to make to the module? Call this version a11_1_1a.py.
   2. Now refactor this code so it uses three classes Circle, Triangle and Square instead of one where each class has its own draw, fill, etc. methods. Call this version a11_1_1b.py.
   3. Finally, what changes have to be made to version a11_1_1b.py to support a new pentagon shape type? Call this version a11_1_1c.py
   4. Compare the changes you made in a. and c. above. In each case how much existing code did you have to modify? Which approach is most likely to result in breaking existing code? You can put your answers to these questions in your submission comment.
2. The class CoinJar represents a jar of Canadian coins. Write the necessary code so this program will run correctly.

   tims = CoinJar(pennies = 3, quarters = 2, loonies = 1,twonies = 0)
   mollys = CoinJar(pennies = 48, nickels = 12, dimes = 7, quarters = 14)
   print tims.value() # Displays 1.53
   print mollys.value() # Displays 5.28
   print tims.dimes # Displays 0.
   print tims[0] # Displays 0.
   print mollys.quarters # Displays 14.
   print mollys[3] # Displays 7.
   if tims > mollys:
       print 'Tim is richer than Molly.'
   else:
       print 'Molly is at least as rich as Tim.'
   # ^ Displays: Molly is at least as rich as Tim.
   tims = tims + mollys
   print tims # Fancy display of your design.

   Hint: Since the order of the parameters varies between the two constructor calls in lines 1 and 2 we can tell that named parameters are being used.

3. The file WumpusAdjMatrixMap.py contains an alternative representation of a wumpus cave system (one based on an adjacency matrix* rather than the list of lists of tunnels we have been using) and stubs for two functions: tunnels_from and tunnels_to. Write the bodies of these functions so they will work as the docstrings describe. The docstrings contain one test of each function, but these are meant to be illustrative rather than exhaustive.

   Note that you don't have to integrate this representation into your earlier Hunt the Wumpus program. This is a stand alone problem.

   Hint: You might want to peek ahead at Module 12 to see how to activate the tests in the docstrings.

Logistics

• Use the following naming scheme for your program files: aassignment#pproblem#vversion#.py . So your first attempt at problem 1 on this assignment will be named a11p1v1.py and your second attempt (should there be one) will be named a11p1v2.py .

• Submit your assignment by emailing your python programs to me. I advise to submit early and submit often, since I will often review your programs as they are submitted and provide feedback that will let you improve them.

* it sounds fancy but as you will see when you take Finite Mathematics it's just a table. Normally students will either have taken Finite Mathematics before this course or be taking it at the same time. If I haven't said enough for you to understand the representation just ask!