Homework 11: Classes

To receive full credit, for each exercise you should do the following:

1. Design: First, design a Python class as requested in the exercise. Type in your class definition.

2. Check: Run the provided test code. Does your actual output agree with the given correct output?

3. Evaluate: If the actual output does not match the expected output, keep experimenting, consult the textbook or Python documentation, ask a friend or TA or professor, etc. until you can fix your class definition and explain what your misunderstanding(s) were. (You do not need to do anything for step 3 if the outputs already agree exactly.)

You should consider the code in each exercise separately from the other exercises.

1. Write a Python class BouncyBall, which represents a bouncy ball containing a certain amount of air.

   • When a BouncyBall object is first created, it should have 10 units of air.
   • There should be a method bounce() which normally prints the word Bounce! and decreases the amount of air in the ball by two units. However, if the amount of air is less than or equal to three, then bounce() does not decrease the amount of air and prints Thupp. instead of Bounce!.
   • There should be a method inflate() which increases the amount of air by three units. If the amount of air ever becomes greater than 12, then the ball explodes by printing BANG!!!.
   • You cannot bounce or inflate an exploded ball. After a ball explodes, calling bounce() or inflate() should just cause a message to be printed such as Sorry, you cannot bounce this ball! It has exploded.

   To test your class, you can type in and run the following code:

    def main():
        b = BouncyBall()
   
        for i in range(6):
            b.bounce()
   
        b.inflate()
        b.bounce()
        b.bounce()
   
        for i in range(5):
            b.inflate()
   
        b.bounce()
   
    main()
   

   If your definition of BouncyBall is correct, main() should produce the following output:

    Bounce!
    Bounce!
    Bounce!
    Bounce!
    Thupp.
    Thupp.
    Bounce!
    Thupp.
    BANG!!!
    Sorry, you cannot inflate this ball!  It has exploded.
    Sorry, you cannot bounce this ball!  It has exploded.
   

2. Write a Python class Gradebook which works as follows:

   • When a new Gradebook object is first created, it should start out with an empty list of grades, and zero points of extra credit.
   • There should be a method add_grade(g: int) which adds the grade g to the end of the list.
   • There should be a method add_ec(ec: int) which adds ec points of extra credit to the current amount of extra credit.
   • There should be a method average() which computes and returns the average of all the grades so far (the sum of all the grades, plus the extra credit score, divided by the number of grades).

   You can test your implementation of Gradebook by running the code below:

    def main():
        gb = Gradebook()
        gb.add_grade(90)
        gb.add_grade(83)
        gb.add_grade(97)
        gb.add_ec(10)
   
        print(gb.average())
   
    main()
   

   If your definition of Gradebook is correct, this should print 93.33333333333333.