CSCI 150 - Lab 11 - Water Jugs

CSCI 150 - Lab 11
Water Jugs

Overview

This lab will combine mathematics, instantiable classes, and bone-chilling terror. ;) Always a famous puzzle in the Artifical Intelligence circles, the WaterJug came to popular culture through the classic action movie Die Hard III. In Die Hard III, a mad bomber is chasing Bruce Willis and Samuel L. Jackson. They must solve different puzzles or else things will explode and people will die.

Example

The WaterJug puzzle can be explained as follows:
You have two jugs, A and B, and an infinite supply of water. There are three actions you can perform: (1) you can fill a jug to capacity, (2) you can completely empty a jug, and (3) you can pour from one jug to the other. Pouring from one jug to the other stops when the first jug is empty or the second jug is full, whichever comes first. For example, if A has 5 gallons and B has 6 gallons and a capacity of 8, then pouring from A to B leaves B full and 3 gallons in A.

For this demonstration, we'll state that A has capacity 4 and B has capacity 3. Our goal, which we must complete in less than one minute, is to somehow get exactly 2 gallons of water in jug A. We need to find a set of operations, filling, emptying, and pouring, where we can reach this goal. One possible solution is as follows:

FILL A
POUR from A to B
EMPTY B
POUR from A to B
FILL A
POUR from A to B

We now have exactly 2 gallons of water jug in A. (Try it!). Phew, we're still alive! Wouldn't it be nice to have a computer program to help us solve this?

Step 1: The WaterJug class

Each WaterJug object will need to have two variables that we can think of as the state of that WaterJug:

Also, a WaterJug needs some functionality to change the state of the internal components. In object-oriented programming, these are called methods.

Methods:

Implement this object in Python. Don't forget where to use the self keyword. Be careful with your methods to make sure a malicious programmer (or buggy code) cannot violate the integrity of your class. For example, it should never be possible to end up with a WaterJug with more contents than capacity.

Your code should go in a file named waterjug.py. At the end of that file, place the following lines of code: 

if __name__ == '__main__':
    test()

Above that, write a function named test() that tests your class and ensures that it works. Make sure your test code uses all of the methods of the class. It should employ if statements to check whether each test passes. If a test fails, it should print an appropriate message. If all tests pass, it should print a success message.

The __repr__ method needs to return a string that, if typed into the Python shell, would reconstruct the original object. The str function calls __repr__ for its argument in order to create its string representation. The eval function calls the Python interpreter to execute its string argument. The following function will test whether __repr__ works for any class: 

def test_repr(obj):
    return str(obj) == str(eval(str(obj)))

Step 2: The Puzzle

In a new file, step2.py, write a program that allows the user to set up and then solve a water jugs puzzle. To use the WaterJug class, you will need the following line at the top of your file: 

from waterjug import WaterJug

Your program should:

It is not necessary to validate user input. For this assignment, you may assume that all user input is valid. Also, you should not just put everything in main, but you should break your code up into functions appropriately.

Step 3: Generalizing

In a new file, step3.py, generalize your program from Step 2 so that it works with any number of WaterJugs instead of just 2. In particular, the program should:

You never know when a Python class could save your life. And remember, "Think fast, Look alive, Die hard."

What to Hand In

Make sure you have followed the Python Style Guide, and have run your project through the Automated Style Checker.

You must hand in:

Grading

© Mark Goadrich and Brent Yorgey, Hendrix College