Problem Set #3 Wordgames

Introduction

In this problem set, you’ll implement two versions of the 6.00 wordgame!

Don’t be intimidated by the length of this problem set. It’s a lot of reading, but it is very doable.

Let’s begin by describing the 6.00 wordgame: This game is a lot like Scrabble or Text Twist, if you’ve played those. Letters are dealt to players, who then construct one or more words out of their letters. Each valid word receives a score, based on the length of the word and the letters in that word.

The rules of the game are as follows:

Dealing

    • A player is dealt a hand of n letters chosen at random (assume n=7 for now).

    • The player arranges the hand into as many words as they want out of the letters, but using each letter at most once.

    • Some letters may remain unused (these won’t be scored).

Scoring

    • The score for the hand is the sum of the score for the words times the length of the word.

    • The score for a word is the sum of the points for letters in the word, multiplied by the length of the word, plus 50 points if all n letters are used on the first go.
    • Letters are scored as in Scrabble; A is worth 1, B is worth 3, C is worth 3, D is worth 2, E is worth 1, and so on. We have defined the dictionary

SCRABBLE_LETTER_VALUES

that maps each lowercase letter to its Scrabble letter value.

    • For example, ‘weed’ would be worth 32 points ((4+1+1+2)*4=32), as long as the hand actually has 1 ‘w’, 2 ‘e’s, and 1 ‘d’.
    • As another example, if n=7 and you get ‘waybill’ on the first go, it would be worth 155 points ((4+1+4+3+1+1+1)*7=105, +50) for the bonus of using all seven letters).

Workload

Please let us know how long you spend on each problem. We want to be careful not to overload you by giving out problems that take longer than we anticipated.

Getting Started

    1. Download and save the Problem Set 3 code files.

    2. Run ps3a.py, without making any modifications to it, in order to ensure that everything is set up correctly. The code we have given you loads a list of valid words from a file and then calls the play_game function. You will implement the functions it needs in order to work.If everything is okay, after a small delay, you should see the following printed out:
    3. Loading word list from file...
83667 words loaded.

If you see an IOError instead (e.g., No such file or directory), you should change the value of the WORDLIST_FILENAME constant (defined near the top of the file) to the complete pathname for the file words.txt (This will vary based on where you saved the file).

    4. The file ps3a.py has a number of already implemented functions you can use while writing up your solution. You can ignore the code between the following comments, though you should read and understand everything else:

    5. # -----------------------------------
    6. # Helper code
    7. # (you don't need to understand this helper code)
8.    .
9.    .
10.    .
    11. # (end of helper code)
    12. # -----------------------------------


    13. This problem set is structured so that you will write a number of modular functions and

then glue them together to form the complete word playing game. Instead of waiting until the entire game is ready, you should test each function you write, individually, before moving on. This approach is known as unit testing, and it will help you debug your code.

We have provided several test functions to get you started. As you make progress on the problem set, run test_ps3a.py as you go.
If your code passes the unit tests you will see a SUCCESS message; otherwise you will see a FAILURE message. These tests aren’t exhaustive. You may want to test your code in other ways too.

If you run test_ps3a.py using the provided ps3a.py skeleton, you should see that all the tests fail.

These are the provided test functions:

test_get_word_score()

Test the get_word_score() implementation.
test_update_hand()
Test the update_hand() implementation.
test_is_valid_word()

Test the is_valid_word() implementation.

Part A

Problem 1. Word scores

The first step is to implement some code that allows us to calculate the score for a single word.

The function get_word_score should accept a string of lowercase letters as input (a word) and return the integer score for that word, using the game’s scoring rules.

Fill in the code for get_word_score in ps3a.py:

def get_word_score(word, n):

"""Returns the score for a word. Assumes the word is a valid word.

The score for a word is the sum of the points for letters in the word, multiplied by the length of the word, plus 50 points if all n letters are used on the first go.

Letters are scored as in Scrabble; A is worth 1, B is worth 3, C is worth 3, D is worth 2, E is worth 1, and so on.

word: string (lowercase letters)

    n: integer (HAND_SIZE; i.e., hand size required for additional points) returns: int >= 0
"""
# TO DO ...

You may assume that the input word is always either a string of lowercase letters, or the empty string "". You will want to use the SCRABBLE_LETTER_VALUES dictionary defined at the top of ps3a.py. You should not change its value.
Do not assume that there are always 7 letters in a hand! The parameter n is the number of letters required for a bonus score (the maximum number of letters in the hand).

Testing: If this function is implemented properly, and you run test_ps3a.py, you should see that the test_get_word_score() tests pass.

Also test your implementation of get_word_score, using some reasonable English words.

Problem 2. Dealing with hands

**Please read problem 2 entirely before you begin coding the solution to problem 2**

Representing hands

A hand is the set of letters held by a player during the game. The player is initially dealt a set of random letters. For example, the player could start out with the following hand:

a, q, l, m, u, i, l

In our program, a hand will be represented as a dictionary: the keys are (lowercase) letters and the values are the number of times the particular letter is repeated in that hand. For example, the above hand would be represented as:

hand = {'a':1, 'q':1, 'l':2, 'm':1, 'u':1, 'i':1}

Notice how the repeated letter 'l' is represented.

Notice that with a dictionary representation, the usual way to access a value is hand['a'], where 'a' is the key we want to find. However, this only works if the key is in the dictionary; otherwise, we get a KeyError. To avoid this, we can use the call hand.get('a',0). This is

the ”safe” way to access a value if we are not sure the key is in the dictionary. d.get(key,default) returns the value for key if key is in the dictionary d, else default. If default is not given, it returns None, so that this method never raises a KeyError.

Converting words into dictionary representation

One useful function we’ve defined for you is get_frequency_dict, defined near the top of ps3a.py. When given a string of letters as an input, it returns a dictionary where the keys are letters and the values are the number of times that letter is represented in the input string. For example:

    • get_frequency_dict("hello") {'h': 1, 'e': 1, 'l': 2, 'o': 1}

As you can see, this is the same kind of dictionary we use to represent hands.
Displaying a hand

Given a hand represented as a dictionary, we want to display it in a user-friendly way. We have provided the implementation for this in the the display_hand function. Make sure you read through this carefully and understand what it does and how it works.

Generating a random hand

The hand a player is dealt is a set of letters chosen at random. We provide you with the implementation of a function that generates this random hand, deal_hand. The function takes as input a positive integer n, and returns a new object, hand containing n lowercase letters.

Removing letters from a hand (you implement this)

The player starts with a hand, a set of letters. As the player spells out words, letters from this set are used up. For example, the player could start out with the following hand:

a, q, l, m, u, i, l

The player could choose to spell the word quail. This would leave the following letters in the player’s hand:

l, m

You will now write a function that takes a hand and a word as inputs, uses letters from that hand to spell the word, and returns the remaining letters in the hand.

For example:

    • hand = {'a':1, 'q':1, 'l':2, 'm':1, 'u':1, 'i':1}

    • display_hand(hand)
a q l l m u i
    • hand = update_hand(hand, 'quail')
    • hand
{'l': 1, 'm': 1}
    • display_hand(hand) l m

(NOTE: alternatively, in the above example, after the call to update_hand the value of hand could be the dictionary {'a':0, 'q':0, 'l':1, 'm':1, 'u':0, 'i':0}. The exact

value depends on your implementation; but the output of display_hand() should be the same in either case.)

Implement the update_hand function. Make sure this function has no side effects; i.e., it cannot mutate the hand passed in.

def update_hand(hand, word):

"""Assumes that 'hand' has all the letters in word.
In other words, assumes that however many times

a letter appears in 'word', 'hand' has at least as many instances of that letter in it.

Updates the hand: uses up the letters in the given word and returns the new hand, without those letters in it.

Has no side effects: does not modify hand.

word: string
hand: dictionary (string -> int)
returns: dictionary (string -> int)
"""
# TO DO ...

Testing: Make sure the test_update_hand() tests pass. You may also want to test your implementation of update_hand with some reasonable inputs.

Problem 3. Valid words

At this point, we have written code to generate a random hand and display that hand to the user. We can also ask the user for a word (Python’s raw_input) and score the word (using

your get_word_score). However, at this point we have not written any code to verify that a word given by a player obeys the rules of the game.

A valid word is in the word list; and it is composed entirely of letters from the current hand.

Implement the is_valid_word function.

def is_valid_word(word, hand, word_list):

"""Returns True if word is in the word_list and is entirely composed of letters in the hand. Otherwise, returns False. Does not mutate hand or word_list. word: string

hand: dictionary (string -> int)
word_list: list (string)
"""
# TO DO ...

Testing:

Make sure the test_is_valid_word tests pass. In particular, you may want to test your implementation by calling it multiple times on the same hand ó what should the correct behavior be?

Problem 4. Playing a hand

We are now ready to begin writing the code that interacts with the player.

Implement the play_hand function. This function allows the user to play out a single hand.
def play_hand(hand, word_list):

"""Allows the user to play the given hand, as follows:
    1) The hand is displayed.
    2) The user may input a word. Alternatively, the user may end the game by entering a period ('.').
    3) An invalid word is rejected, and a message is displayed asking the user to choose another word.
    4) When a valid word is entered, it uses up letters from the hand.
    5) After every valid word: the score for that word is displayed, the remaining letters in the hand are displayed, and the user is asked to input another word.
    6) The sum of the word scores is displayed when the hand finishes.
    7) The hand finishes when there are no more unused letters.
The user may choose to end the hand at any time by inputting a single period (the string '.') instead of a word.

hand: dictionary (string -> int)

word_list: list (string)
"""
# TO DO ...

Testing: Try out your implementation as if you were playing the game.

Note: Do not assume that there will always be 7 letters in a hand! The global variable

HAND_SIZE represents this value. Here is some example output of play_hand (your output may differ, depending on what messages you print out):

Case #1

Current Hand:    a c i h m m z

Enter word, or a "." to indicate that you are finished: him
"him" earned 24 points. Total: 24 points

Current Hand:    a c m z

Enter word, or a "." to indicate that you are finished: cam
"cam" earned 21 points. Total: 45 points

Current Hand:    z

Enter word, or a "." to indicate that you are finished: .
Total score: 45 points.

Case #2

Current Hand:    a s t t w f o

Enter word, or a "." to indicate that you are finished: tow
"tow" earned 18 points. Total: 18 points

Current Hand:    a s t f

Enter word, or a "." to indicate that you are finished: tasf Invalid word, please try again.

Current Hand:    a s t f

Enter word, or a "." to indicate that you are finished: fast
"fast" earned 28 points. Total: 46 points.

Total score: 46 points.

Problem 5. Playing a game

A game consists of playing multiple hands. We need to implement one final function to complete our word-game program.

Write the code that implements the play_game function. You should remove the code that is currently uncommented in the play_game body. Read through the specification and make sure you understand what this function accomplishes.

For the game, you should use the HAND_SIZE constant to determine the number of cards in a hand. If you like, you can try out different values for HAND_SIZE with your program.

def play_game(word_list):

"""Allow the user to play an arbitrary number of hands.

    1) Asks the user to input 'n' or 'r' or 'e'.

        ◦ If the user inputs 'n', let the user play a new (random) hand.
        ◦ If the user inputs 'r', let the user play the last hand again.
        ◦ If the user inputs 'e', exit the game.
        ◦ If the user inputs anything else, ask them again.

    2) When done playing the hand, repeat from step 1

"""
# TO DO ...

Testing: Try out this implementation as if you were playing the game.

Part B

**Part B is dependent on your functions from ps3a.py, so be sure to complete ps3a.py before working on ps3b.py**

You decide to teach your computer (SkyNet) to play the game you just built so that you can prove once and for all that computers are inferior to human intellect. In Part B you will make a modification to the play_hand function from part A.

Problem 6A: Computer Word Choose

First we must create a function that allows the computer to choose a word.

We have provided the function get_perms(hand, n) (defined in perm.py, but usable by simply calling get_perms(hand, n)). The specification is as follows:

def get_perms(hand, n):
"""Takes in the current hand and a number which

must be less than or equal to the size of the hand. It returns all possible permutations of size n given the letters in the hand.

hand: dictionary (string -> int)

    n: int bounded by 0 < n >= len(hand) returns list (string)
"""
#IMPLEMENTED...

You are not required to know how get_perms works.

It is your responsibility to create the function comp_choose_word(hand, word_list)

def comp_choose_word(hand, word_list):

"""Given a hand and a word_list, find a valid word, and return it.

hand: dictionary (string -> int)

word_list: list (string)
"""
# TO DO ...

Hint: First try to make a legal player, and then worry about making the computer player better (if you have time).

Problem 6B. Computer’s turn to play a hand

Now you need to write a function similar to Part A’s play_hand.

Implement the comp_play_hand function. This function should allow the computer to play the game through completion.

def comp_play_hand(hand, word_list):

"""Allows the computer to play the given hand, as follows:

    1) The hand is displayed.

    2) The computer chooses a word.
    3) After every valid word: the score for that word is displayed, the remaining letters in the hand are displayed, and the computer chooses another word.
    4) The sum of the word scores is displayed when the hand finishes.
    5) The hand finishes when the computer has exhausted its possible choices (i.e. comp_play_hand returns None).

hand: dictionary (string -> int)

word_list: list (string)
"""
# TO DO ...

Problem 6C: U & Ur Computer

Now that your computer can choose a word, you need to give the computer the option to play.
Write the code that re-implements the play_game function. You will modify the function to behave as described below in the function’s comments.

As before, you should use the HAND_SIZE constant to

determine the number of cards in a hand. If you like, you can try out different values for HAND_SIZE with your program.

def play_game(word_list):

"""Allow the user to play an arbitrary number of hands.

    1) Asks the user to input 'n' or 'r' or 'e'.

        ◦ If the user inputs 'n', play a new (random) hand.
        ◦ If the user inputs 'r', play the last hand again.
        ◦ If the user inputs 'e', exit the game.
        ◦ If the user inputs anything else, ask them again.

    2) Ask the user to input a 'u' or a 'c'.

        ◦ If the user inputs 'u', let the user play the game as before using play_hand.
        ◦ If the user inputs 'c', let the computer play the game using
comp_play_hand (created above).
        ◦ If the user inputs anything else, ask them again.

    3) After the computer or user has played the hand, repeat from step 1

word_list: list (string)

"""
# TO DO ...

This completes the problem set!

Hand-in Procedure

    1. Save

Save your solution to Part A in a file: ps3a.py.
Likewise, save your solution to Part B: ps3b.py.
Do not ignore this step or save your file(s) with a different name!

    2. Time and collaboration info

At the start of the file, in a comment, write down the number of hours (roughly) you spent on this problem set, and the names of whomever you collaborated with. For example:
    3. # Problem Set 3a
    4. # Name: Jane Lee
    5. # Collaborators: John Doe
    6. # Time: 3 hours 30 minutes
    7. #
.... your code goes here ...

Be sure to do the same for ps3b.py.

    8. Submit
MIT OpenCourseWare
http://ocw.mit.edu



6.00SC Introduction to Computer Science and Programming

Spring 2011




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