In this class, we will build a rock paper scissors game^[1] we can play with the computer. It’s better to type the code in an editor so you can save it.

Class 2

• Flow chat
• Get player’s input
• Generate a random shape
• Who won ?
• All code
• Challenge

Flow chart ↑

Toggle the following flow chart to help you understand the logic behind our code.

flowchart TD
    A["Start: n = 0, w = 0"]
    A--> B{n < 5?}
    B -- Yes --> C["wait_for_player_input()"]
    C-->C1{Valid?}
    C1--Yes--> D["random_shape()"]
    C1--No -->C
    D --> E{"who_won()"}
    E -- Player --> F[w += 1]
    E -- Computer --> G[ n += 1]
    E -- Tied --> B
    F-->G
    G-->B
    B -- No ----> H[Show Results]
    H-->I[End]

Get player’s input ↑

def wait_for_player_input():
    shape = input("Rock (r), Paper (p), Scissors (s) ? ")
    if shape in ["r", "p", "s"]:
        return shape
    else:
        return wait_for_player_input()

Attention: a function that call itself is called recursive function.

Generate a random shape ↑

We will need to import a function from a python module, put this line at the beginning of your file.

import random

Let’s create a function to return a random shape as computer’s input

def random_shape():
    random.choice(['r', 'p', 's'])

Who won? ↑

Return 0 for tie, 1 if player won, 2 if computer won.

def who_won(pshape, cshape):
    if pshape == cshape:
        return 0
    r = pshape + cshape
    if r == 'rs' or r == 'pr' or r == 'sp':
        return 1
    return 2

All code ↑

Let’s write the main game logic and put all code together.

import random

def wait_for_player_input():
    shape = input("Rock (r), Paper (p), Scissors (s) ? ")
    if shape in ["r", "p", "s"]:
        return shape
    else:
        return wait_for_player_input()

def random_shape():
    return random.choice(['r', 'p', 's'])

def who_won(pshape, cshape):
    if pshape == cshape:
        return 0
    r = pshape + cshape
    if r == 'rs' or r == 'pr' or r == 'sp':
        return 1
    return 2

def play(n_game):
    n = 0
    w = 0
    while n < n_game:
        print(f"Game # {n + 1}")
        pshape = wait_for_player_input()
        cshape = random_shape()
        print(f"Computer: {cshape}")
        match who_won(pshape, cshape):
            case 0:
                print("Tied! Replay")
                continue
            case 1:
                print("You got this one!")
                w += 1
            case 2:
                print("Computer got this one!")
        print()
        n += 1
    print(f"You got {w} out of {n_game}")
    if w > n_game / 2:
        print("You WON!")
    else:
        print("You LOST!")

play(3)

Attention: make sure your python version is 3.10 or above to use match statement.

Challenge ↑

1. Create a new function play_till(n_won) so that whoever won n_won first, won the whole game.

Leave a comment if you have any questions (you don’t need to register an account).

Class 1

1. Wikipedia: Rock Paer Scissors ↩