The goal of this lab is to use the top-down design that you created last week to now do a bottom-up implementation of the game of Ghost. Each function should be unit tested as it is implemented.

Do an update21 to create the directory cs21/lab/07. Copy the design that you did last week to the current lab directory, and then change into that directory as shown below:

$ update21
$ cp cs21/lab/06/ghost.py cs21/lab/07
$ cd cs21/lab/07

Edit the file ghost.py that is in the cs21/labs/07/ directory. The program handin21 will only look for files in this directory.

If you worked with a partner on the previous lab, you may continue to work with the same partner on this lab. If you work with a partner, be sure to put your name and the name of your partner in the list of authors at the top of your program. Only one partner needs to run handin21 to submit the files for the group. Both partners will receive the same grade.

You will implement a program that plays the word game Ghost using your top-down design as a starting point. Be sure to read carefully through all of the comments on your design from Lab 6 before you begin to construct your solution for Lab 7.

• Your program should use the online word list stored in the file /usr/share/dict/words. Your program should open this file one time, read in all of the valid words (length four or longer, not proper nouns, and not containing an apostrophe) and store them in a list, and then close the file.
• The computer player should always select a valid letter, if one exists. Otherwise it should challenge the human player.
• Your program should ensure that the user selects a valid menu option.
• Your program should ensure that when the user chooses to add a letter that they enter a valid letter.
• Your program should have the following lines at the bottom to allow you to import the program without running main so that you can do unit testing.

  if __name__ == '__main__':
     main()
  

• To do unit testing, change directories into the current lab directory, invoke python, and import your program. Then you can test individual functions. Suppose you have a function called randomLetter() that returns a random letter of the alphabet. You could test it as shown below:

  $ cd cs21/labs/07
  $ python
  >>> from ghost import *
  >>> randomLetter()
  c
  >>> randomLetter()
  t
  >>> randomLetter()
  e
  

Notice in the following example that the user makes several mistakes, choosing an invalid menu option and failing to provide a valid letter. Your program should check for these errors and give the user a chance to try again.

Welcome to the game of Ghost.

The current word fragment is: q

1. Add a letter
2. Challenge
Choice: 3
Invalid choice, try again.

1. Add a letter
2. Challenge
Choice: 1
Enter a letter: 5
Invalid letter, try again.
Enter a letter: u
The current word fragment is: qu

Computer will add the letter: a
The current word fragment is: qua

1. Add a letter
2. Challenge
Choice: 1
Enter a letter: r
The current word fragment is: quar

Computer will add the letter: t
Computer just made the word quart

Congratulations, you just outsmarted the computer!

These suggestions are not required and should only be attempted when all of the required elements of the program are working.

• Rather than playing a single game, the program could play a series of games and keep track of how many times the user wins and the computer wins.
• If the computer is about to lose the game (because it only has one option and that will make a word), it can try to bluff by choosing a random letter instead.
• Make the computer smarter in how it selects which letter to add to the word fragment. Rather than selecting any appropriate letter, you could look at all of the viable words and try to select one that gives the computer the best chance of winning.

Once you are satisfied with your program, hand it in by typing handin21 in a terminal window.