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. YOU DO NOT ACTUALLY HAVE TO DRAW OR MANIPULATE SHAPES! This is just an example of how to implement good object oriented design.

    # 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
        ...
    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))

    a. 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.

    b. 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.

    c. 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

    d. 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,toonies=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.

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