3. RPS dictionary

3.1. Python Game design

This version of the game code uses a dictionary for the results.

Each item in the dictionary has a key.

Each key in the dictionary is a 2-tuple with the user choice first followed by the computer choice.

There is a key for all nine possible combinations.

Each item has a value indicating the winner or a tie.

To look up the results dictionary use: winner = results.get(combo, 'invalid entry'). This is able to handle the use of a key that does not exist.

This is better than winner = results[combo] since if the user entry is not a proper choice, an error results.

import random

results = {
    ('rock', 'rock'): 'tie',
    ('rock', 'paper'): 'computer',
    ('rock', 'scissors'): 'human',
    ('paper', 'rock'): 'human',
    ('paper', 'paper'): 'tie',
    ('paper', 'scissors'): 'computer',
    ('scissors', 'rock'): 'computer',
    ('scissors', 'paper'): 'human',
    ('scissors', 'scissors'): 'tie',
}


num_games = int(input('How many games would you like to play? '))

for i in range(num_games):
    computer_move = random.choice(['scissors', 'paper', 'rock'])
    human_move = input('Type your move: rock, paper or scissors. ')
    results_key = (human_move, computer_move)

    print('Computer Played: ' + computer_move)
    print('Human Played: ' + human_move)
    # winner = results[combo]
    winner = results.get(results_key, 'invalid entry')
    if winner == 'invalid entry':
        print('invalid entry')
    elif winner == 'tie':
        print('Tie!')
    else:
        print(winner + ' wins')

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Tasks

1. Modify the python code to use R, P or S instead of rock, paper or scissors throughout the code.

2. Add counters so that the total wins, losses and draws is printed after each game in python.

3. Modify the code to ask for a valid move from the use by placing the human move in a while loop and test to see if the move is a list or tuple of valid moves.

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3.2. Microbit version

The Microbit version of the game code, using a dictionary for the results, is below.

from microbit import *
import random


results = {
    ('R', 'R'): 'tie',
    ('R', 'P'): 'computer',
    ('R', 'S'): 'human',
    ('P', 'R'): 'human',
    ('P', 'P'): 'tie',
    ('P', 'S'): 'computer',
    ('S', 'R'): 'computer',
    ('S', 'P'): 'human',
    ('S', 'S'): 'tie',
}

display.scroll('A for R   B for P   A&B for S', delay=80)

while True:
    microbit_move = random.choice(['R', 'P', 'S'])
    while True:
        # short pause to allow time to hold down 2 buttons
        sleep(300)
        if button_a.is_pressed() and button_b.is_pressed():
            human_move = 'S'
            break
        elif button_a.is_pressed():
            human_move = 'R'
            break
        elif button_b.is_pressed():
            human_move = 'P'
            break

    display.scroll(human_move + ' v ' + microbit_move, delay=60)

    results_key = (human_move, microbit_move)
    winner = results.get(results_key, 'invalid entry')

    if winner == 'invalid entry':
        display.show(Image.MEH)
    if winner == 'tie':
        display.show('=')
    elif winner == 'human':
        display.show(Image.YES)
    elif winner == 'computer':
        display.show(Image.NO)

    sleep(500)
    display.clear()

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Tasks

1. Modify the microbit code so that after the first game, arrows to the A button and B button are shown to prompt the user to play another game.

2. Add counters so that the total wins, losses and ties is scrolled after each game. e.g. ‘W3 L2 T4’

3. Use if-else after each game to ask to continue playing by pressing the A button or to exit by pressing the B button.

4. Modify the display of the R, P or S to use custom images instead.