Rock, Paper, Scissors

Follow the instructions below to create a simple Rock Paper Scissors game in Python!

Setting Up

Set up by creating a new Replit project.

1. Go to Replit
2. Log in
3. Create a new Python Repl project named "Rock Paper Scissors"

Player Input

The first step is to welcome the player to the game, and ask which move they would like to make.

1. Use a print statement to say "Welcome to Rock Paper Scissors!"
2. On the next line, use input to ask the user for a move - "Enter R, P, or S: "
3. Store the result of the input in a new variable named player_move

The code should look something like this:

print("Welcome to Rock Paper Scissors!")

player_move = input("Enter R, P, or S: ")

Computer Choice

Now the player has made a move, it's time to choose a move for the computer! The computer's move should be chosen randomly. Using a Python library, it will be possible to generate a random choice from a set of options ("R", "P", and "S").

1. At the top of the file, use import random to import the random library into the program
   • This provides a random object with a choice function
2. Under where the player_move is selected, create a new variable named computer_move
3. Set the computer_move variable to be random.choice("RPS")
   • This will choose either "R", "P", or "S" at random

The code should look something like this:

import random

print("Welcome to Rock Paper Scissors!")
player_move = input("Enter R, P, or S: ")

computer_move = random.choice("RPS")

Basic Battling

Now the player has a move, and the computer has a move... but which will win? Take a look at this table for a refresher on the rules of Rock Paper Scissors:

In total, there are 9 possible outcomes. That's quite a lot, so instead of trying to code all 9, start with that first row.

There are three options:

• Player chooses rock, Computer chooses rock → tie
• Player chooses rock, Computer chooses paper → loss
• Player chooses rock, Computer chooses scissors → win

These all start the same: player chooses rock. That is the first condition for each of these outcomes. In the code, under the computer_move line, create an if statement that checks if the player chose rock:

if player_move == "R":

And what should happen if the player chooses rock? Well, it depends on what the computer chose!

Rock v. Rock

Say the computer chose rock as well. That would be the next condition, still within the scope of this first condition:

if player_move == "R":
    if computer_move == "R":

Now, in the block within the second condition, it is known that the player chose rock, AND the computer chose rock. And what should happen in that case? It will be a tie! Print out a message saying as much.

if player_move == "R":
    if computer_move == "R":
        print("Rock v. Rock: Tie")

Run the program, enter "R", and see what happens. It should only print something if the computer chooses rock.

Rock v. Paper

Add code to handle the case when the computer chooses paper (after the player chose rock). This should be within the block of player_move == "R", under the computer_move == "R" statement.

1. Add an elif checking if the computer chose paper (indented 1 level)
2. Within that new elif block, create a print statement (indented 2 levels)
3. Add the result - "Rock v. Paper: Computer Wins"

Rock v. Scissors

Add code to handle the case when the computer chooses scissors (after the player chose rock). This should, again, be within the block of player_move == "R", under the computer_move == "R" statement.

1. Add an elif checking if the computer chose scissors (indented 1 level)
2. Within that new elif block, create a print statement (indented 2 levels)
3. Add the result - "Rock v. Scissors: Player Wins"

Testing the Code

At this point, the if statement should look something like this:

if player_move == "R":
    if computer_move == "R":
        print("Rock v. Rock: Tie")
    elif computer_move == "P":
        print("Rock v. Paper: Computer Wins")
    elif computer_move == "S":
        print("Rock v. Scissors: Player Wins")

Run the program, and make sure that all outcomes are possible to reach. They should occur with approximately equal frequency.

A Battling Function

So far, the program is working, but it is becoming a little unwieldy. Before adding in the other outcomes, define a function to handle the battling outcomes to clear up the main game code.

1. Right under the import random statement, create some space in the code
2. Define a new function named battle
   • The function should take in a player parameter (for the player's move)
   • The function should also take in a computer parameter (for the computer's move)
3. Copy the big if statement, and paste it into the body of the battle function
   • Make sure it is indented one extra level under the definition line
4. Change computer_move and player_move to computer and player (respectively)

The function definition should look like this:

def battle(player, computer):
    if player == "R":
        if computer == "R":
            print("Rock v. Rock: Tie")
        elif computer == "P":
            print("Rock v. Paper: Computer Wins")
        elif computer == "S":
            print("Rock v. Scissors: Player Wins")

Now, all that's left is to call the battle function! Call it at the bottom of the file, passing in the player_move and computer_move values.

battle(player_move, computer_move)

Run the code, and verify that it behaves in the same way. This was an example of refactoring; the code changed, but the functionality stayed the same.

All Battle Results

The next step is to modify the battle function to include all possible results. There are 6 remaining results to add:

• Player chooses Paper:
  • Computer chooses Rock: Win
  • Computer chooses Paper: Tie
  • Computer chooses Scissors: Loss
• Player chooses Scissors:
  • Computer chooses Rock: Loss
  • Computer chooses Paper: Win
  • Computer chooses Scissors: Tie

Handle each outcome in the battle function.

1. Under the if, add an elif checking if the player selected paper
2. Indented one additional level, check the three computer options
3. Print the result for each outcome
4. Under the player paper elif, check if the player selected scissors
5. Again indented one level under, check the three computer options
6. Print the results for each outcome

The code added code should look something like this:

elif player == "P":
    if computer == "R":
        print("Paper v. Rock: Player Wins")
    elif computer == "P":
        print("Paper v. Paper: Tie")
    elif computer == "S":
        print("Paper v. Scissors: Computer Wins")
elif player == "S":
    if computer == "R":
        print("Scissors v. Rock: Computer Wins")
    elif computer == "P":
        print("Scissors v. Paper: Player Wins")
    elif computer == "S":
        print("Scissors v. Scissors: Tie")

Run the program a few more times, and test out the different paths! Try to reach every outcome.

Game Loop

Now the game is complete, but it would be nice if rematches were a little easier. Create a game loop that will allow the player to play again as often as desired.

1. Above the "Welcome" message, create a new variable named playing
2. Set the playing variable to equal "y"
3. Under that, create a while loop that will continue as long as playing is equal to "y"
4. Indent the main game code, so that it is within the while loop code block
5. Find the bottom of the while loop block, still within the same scope
6. Create an input statement asking "Would you like to play again (y/n)? "
7. Set the playing variable to be the result of the input

The code should look something like this:

playing = "y"
while playing == "y":
    print("Welcome to Rock Paper Scissors!")

    player_move = input("Enter R, P, or S: ")
    computer_move = random.choice("RPS")

    battle(player_move, computer_move)

    playing = input("Would you like to play again (y/n)? ")

Run the program, and make sure it is possible to play multiple times!

Final Code

import random

def battle(player, computer):
    if player == "R":
        if computer == "R":
            print("Rock v. Rock: Tie")
        elif computer == "P":
            print("Rock v. Paper: Computer Wins")
        elif computer == "S":
            print("Rock v. Scissors: Player Wins")
    elif player == "P":
        if computer == "R":
            print("Paper v. Rock: Player Wins")
        elif computer == "P":
            print("Paper v. Paper: Tie")
        elif computer == "S":
            print("Paper v. Scissors: Computer Wins")
    elif player == "S":
        if computer == "R":
            print("Scissors v. Rock: Computer Wins")
        elif computer == "P":
            print("Scissors v. Paper: Player Wins")
        elif computer == "S":
            print("Scissors v. Scissors: Tie")

playing = "y"
while playing == "y":
    print("Welcome to Rock Paper Scissors!")

    player_move = input("Enter R, P, or S: ")
    computer_move = random.choice("RPS")

    battle(player_move, computer_move)

    playing = input("Would you like to play again (y/n)? ")

Challenges

After the activity, start working on the Rock Paper Scissors Challenges.