Tutorial 2: Mastermind

Exercise 1: Loops

Mastermind is played using ‘codes’. A code is a list of four elements (“colors”) which each are chosen among the six colors 'RED', 'GREEN', 'BLUE', 'PURPLE', 'BROWN', and 'YELLOW' (with repetitions).

We will use a global variable for the colors. Add the following line to your file mastermind.py:

COLORS = ['RED', 'GREEN', 'BLUE', 'PURPLE', 'BROWN', 'YELLOW']

Warning: we use the American spelling “colors”, and not the British “colours”, throughout this tutorial. Be careful to follow this convention: if you try to use COLOURS, then Python won’t know what this is!

Solving the exercises on this sheet requires using loops in Python. Thus, we will now create a function that uses a for loop to check if the given color exists in our list of COLORS.

Here’s a start:

def input_color(color):
    """Return True if the given input color can be found in COLORS."""
    # Use a for-loop to iterate over the list of COLORS.
    for i in range(6):
        pass # remove this line and replace with your own code

You might prefer to iterate directly over the COLORS list, rather than using indices!

Testing

Test your code in the console, after running mastermind.py. Make sure you can reproduce the following examples:

In [1]: input_color('BROWN')
Out[1]: True

In [2]: input_color('WHITE')
Out[2]: False

In [3]: input_color('CUCUMBER')
Out[3]: False

Now you can upload your solution using the form below, for further automatic testing.

Exercise 2: Create a random code

We will be playing our game against the computer, so the first thing we need is a function which can create a random code.

Now define a new function create_code (in mastermind.py) which takes no arguments and returns a 4-element list of strings randomly chosen among the six colors above.

Here’s a start:

def create_code():
    """Return 4-element list of strings randomly chosen from
    COLORS with repetition.
    """
    pass # remove this line and replace with your own code

Hints:

• Remember to import random.
• if s is a list, then random.choice(s) returns a random element of s.
• if s is a list, then command s.append(a) will add element a as the last element of the list.

Testing

Test your code in the console, after running mastermind.py. Here’s what your output should look like (but of course, it’s random, so it will not exactly look like this):

In [4]: create_code()
Out[4]: ['RED', 'RED', 'GREEN', 'BROWN']

In [5]: create_code()
Out[5]: ['PURPLE', 'YELLOW', 'PURPLE', 'BLUE']

Upload your solution using the form below for further automatic testing.

Exercise 3: Guess a code

Next we implement functions which allow us to guess a code and receive feedback from the codemaker. The feedback is given as follows:

• For each pin of the right color in the correct position, the codemaker gives a 'BLACK' pin.
• For each pin of a right color, but in the wrong position, we receive a 'WHITE' pin.

For example, if the code is ['RED', 'RED', 'GREEN', 'YELLOW'] and we guess ['RED', 'YELLOW', 'YELLOW', 'BROWN'], then we receive one black pin (for guessing the first 'RED') and one white pin (for guessing the 'YELLOW' in the wrong position; note that the second YELLOW guess doesn’t score an extra pin, as there is only one YELLOW pin in the code).

We will first take care of the black pins. Define a new function black_pins (in mastermind.py) which

• takes two arguments, a guess and a code; and
• the number of black pins that we receive for the guess.

That is, we expect the following behavior:

In [6]: black_pins(['RED', 'BLUE', 'YELLOW', 'BROWN'], ['RED', 'RED', 'GREEN', 'YELLOW'])
Out[6]: 1

In [7]: black_pins(['RED', 'BLUE', 'BROWN', 'YELLOW'], ['RED', 'RED', 'GREEN', 'YELLOW'])
Out[7]: 2

Here is the start of your function:

def black_pins(guess, code):
    """guess, code: 4-element lists of strings from COLORS
    Returns the number of black pins, determined by the standard
    Mastermind rules
    """
    pass # remove this line and replace with your own code

Testing

Test your code in the console, after running mastermind.py. Start by reproducing the examples above (exactly). Now think of some other tests to make sure your code is correct.

Finally, upload your solution using the form below, and it will be tested automatically.

Exercise 4: Guess a code, suite

Now we write a function to determine the number of all pins (black and white) and use it (together with the function from the previous exercise) to find the number of white pins. Remember that according to the Mastermind rules, we receive a pin for every guess of a right color but maybe in a wrong position. That is, we have to compare the modified lists as unordered lists.

Define a new function score_guess (in mastermind.py) that

• takes two arguments, a guess and a code;
• runs black_pins to determine the number of black pins;
• computes the number of all pins, that is the number of colors we guessed correctly (regardless of their position), for example, as follows:
  • for each color, you can find the number of correct guesses of the color as the minimum of the number of occurences of the color in the code and in the guess;
  • the total number of pins will be the sum of these minimums over all colors;
  • substract the number of black pins from the total number of pins to get the number of white pins
• and then returns a tuple (black, white) containing the number of BLACK and WHITE pins in the feedback.

Here’s a start:

def score_guess(guess, code):
    """guess, code: 4-element lists of strings
    Return (black, white) where
    black is the number of black pins (exact matches), and
    white is the number of white pins (correct colors in wrong places)
    """
    black = black_pins(guess, code)
    # remove this line and complete the function with your own code

Here’s what we expect to happen in the console, once you’ve run mastermind.py:

In [8]: score_guess(['RED', 'GREEN', 'YELLOW', 'BLUE'], ['RED', 'YELLOW', 'BROWN', 'RED'])
Out[8]: (1, 1)

In [9]: score_guess(['RED', 'GREEN', 'YELLOW', 'YELLOW'], ['RED', 'YELLOW', 'BROWN', 'RED'])
Out[9]: (1, 1)

In [10]: score_guess(['RED', 'RED', 'RED', 'YELLOW'], ['RED', 'YELLOW', 'BROWN', 'RED'])
Out[10]: (1, 2)

In [11]: score_guess(['RED', 'YELLOW', 'BROWN', 'RED'], ['RED', 'RED', 'RED', 'YELLOW'])
Out[11]: (1, 2)

Hints:

• There is a built-in function count in Python, see the docs.;
• Example run:
  • let’s say the function is called by: score_guess(['RED', 'RED', 'GREEN', 'YELLOW'], ['RED', 'GREEN', 'YELLOW', 'BROWN']);
  • then, we first run black_pins(['RED', 'RED', 'GREEN', 'YELLOW'], ['RED', 'GREEN', 'YELLOW', 'BROWN']) which will return 1;
  • for each color in COLORS, count occurences in guess and code: for RED we get 2 and 1, for GREEN 1 and 1, for BLUE 0 and 0, for PURPLE 0 and 0, for BROWN 0 and 1, and for YELLOW 1 and 1;
  • for each COLOR, we take the minimal value, thus we get 1, 1, 0, 0, 0 and 1 and take the sum of those which is 3;
  • three is the total number of pins that will be shown, however, as we have already calculated that we return 1 black pin, the number of white pins is 2.

Testing

Now test your solution. Start by trying the four examples above, and make sure that you reproduce the output exactly. Then, think of some new tests of your own.

Finally, upload your solution to the form below for further automatic testing.

Exercise 5: User input

We will also need a function which lets the user input a guess.

Define a function input_guess which

• prints Enter your guess: and lets the user input four colors from COLORS,
• prompting the user first for a 1st color:, then a 2nd color: etc.,
• and returns the guess as a list of four colors.

Your function needs to make sure that the user inputs colors which are contained in COLORS. If the user enters a color that is not in COLORS, then your program should ask them to try again.

Complete the following function, adding it to your program mastermind.py:

def input_guess():
    """Input four colors from COLORS and return as list."""
    pass # remove this line and replace with your code

Hints:

• Hit ctrl-C in the console if your code “hangs” on an input.
• Use the str_with_suffix function from last week to convert numbers to ordinal strings.
• Use your function input_color to check if the entered color is correct.

Testing

Test your code in the console, after running mastermind.py:

In [12]: input_guess()
Enter your guess:

1st color: RED

2nd color: YELLOW

3rd color: MAUVE
Please input a color from the list ['RED', 'GREEN', 'BLUE', 'PURPLE', 'BROWN', 'YELLOW']

3rd color: BROWN

4th color: RED
Out[12]: ['RED', 'YELLOW', 'BROWN', 'RED']

Upload your solution to the form below, it will be tested automatically.

Exercise 6: Playing one round of the game

We are now ready to implement one round of the Mastermind game.

Define a function one_round (in mastermind.py) which

• uses input_guess to request input from the user,
• uses score_guess to determine the number of black and white pins to award,
• prints the number of black and white pins,
• and returns True if the user has won, and False otherwise.

Complete the following function, adding it to your program mastermind.py:

def one_round(code):
    """Input guess, score guess, print result, and return True iff
    user has won.
    """
    pass # remove this line and replace with your code

Testing

Test your code in the console, after running mastermind.py. First, make sure you can reproduce the following examples exactly:

In [13]: one_round(['YELLOW', 'RED', 'BROWN', 'RED'])
Enter your guess:

1st color: RED

2nd color: RED

3rd color: RED

4th color: BLUE
Score: 1 black, 1 white
Out[13]: False

In [14]: one_round(['YELLOW', 'RED', 'BROWN', 'RED'])
Enter your guess:

1st color: YELLOW

2nd color: RED

3rd color: BROWN

4th color: RED
Score: 4 black, 0 white
Out[14]: True

Now see if you can think of some more tests to catch possible bugs.

Finally, upload your solution using the form below for further automatic testing.

Exercise 7: Mastermind!

Now we can finally bind things together to play Mastermind against the computer.

Define a function play_mastermind (in mastermind.py) that

• takes a code as input,
• lets the user play in rounds, keeping track of how many rounds have been played,
• until the user has won, in which case it prints You win!

Here’s a start:

def play_mastermind(code):
    """Let user guess the code in rounds."""
    # Hint: use a while loop!
    pass # remove this line and replace with your own code

Here’s what we expect to happen in the console, once you’ve run your code:

In [15]: play_mastermind(['PURPLE', 'GREEN', 'YELLOW', 'BLUE'])

Round 1
Enter your guess:

1st color: PURPLE

2nd color: BLUE

3rd color: YELLOW

4th color: BROWN
Score: 2 black 1 white

Round 2
Enter your guess:

1st color: PURPLE

2nd color: GREEN

3rd color: YELLOW

4th color: BLUE
Score: 4 black 0 white
You win!

Testing

Test your code using the examples above in the console, after running mastermind.py. Make sure you can reproduce them exactly! Can you think of any more useful tests!

Finally, upload your solution using the form below, it will be tested automatically.