如何在 python 中允许输入为小写和大写？

Question

Here is my code. I'm trying to make a rock, paper, scissors game for a school project.

import random

choices = ["Rock", "Paper", "Scissors"]

player_choice = input("Rock, Paper, Scissors?").lower()

while player_choice not in choices:
    player_choice = input("Rock, Paper, Scissors?").lower()

computer_choice = random.randint(0,2)
if computer_choice == 0:
    cpu_choice = choices[0]
elif computer_choice == 1:
    cpu_choice = choices[1]
elif computer_choice == 2:
    cpu_choice = choices[2]

print()
print("You play:", player_choice)
print("The computer plays:", cpu_choice)
print()

if player_choice == "Rock":
    if cpu_choice == choices[0]:
        print("Draw")
    elif cpu_choice == choices[1]:
        print("You Lose :((")
    else:
        print("You win!! :>>")
if player_choice == "Paper":
    if cpu_choice == choices[0]:
        print("You win!! :>>")
    elif cpu_choice == choices[1]:
        print("Draw")
    else:
        print("You Lose :((")
if player_choice == "Scissors":
    if cpu_choice == choices[0]:
        print("You Lose :((")
    elif cpu_choice == choices[1]:
        print("You Win!!! :>>")
    else:
        print("Draw")

The result you get is: Rock, Paper, Scissors?rock Rock, Paper, Scissors?Rock Rock, Paper, Scissors?Rock

and it keeps going like this even though rock is part of choices. This also happens if I input scissors in lowercase or paper.

Answer 1

You can convert your input as well as the concerned comparing value into the same case whether it may be in lowercase or uppercase by using .lower() or .upper() .
Or while comparing like if player_choice.lower() == 'rock' ,
player_choice = player_choice.lower()

Answer 2

Here is another approach that you could consider:

If your choices options need to be capitalized, if you capitalize the player_choice input, the user's input would then be able to match the choices options. This can be done with capitalize() .

Also, instead of having to worry about perfect uppercase or lowercase matching, you could try using regular expression matching using the re module. The matching could be done using re.match() with a special flag called re.IGNORECASE that lets you ignore the case of the words that are being checked.

Additionally, it might be a good idea to use elif: statements after the first if: statement for this type of check.

I also added a space at the end of the initial input questions text for readability.

Here is an example of what these changes could look like:

import random
import re

choices = ["Rock", "Paper", "Scissors"]

player_choice = input("Rock, Paper, Scissors? ").capitalize()

while player_choice not in choices:
    player_choice = input("Rock, Paper, Scissors? ").lower()

computer_choice = random.randint(0,2)
if computer_choice == 0:
    cpu_choice = choices[0]
elif computer_choice == 1:
    cpu_choice = choices[1]
elif computer_choice == 2:
    cpu_choice = choices[2]

print()
print("You play:", player_choice)
print("The computer plays:", cpu_choice)
print()

if re.match("rock", player_choice, flags=re.IGNORECASE):
    if cpu_choice == choices[0]:
        print("Draw")
    elif cpu_choice == choices[1]:
        print("You Lose :((")
    else:
        print("You win!! :>>")
elif re.match("Paper", player_choice, flags=re.IGNORECASE):
    if cpu_choice == choices[0]:
        print("You win!! :>>")
    elif cpu_choice == choices[1]:
        print("Draw")
    else:
        print("You Lose :((")
elif re.match("Scissors", player_choice, flags=re.IGNORECASE):
    if cpu_choice == choices[0]:
        print("You Lose :((")
    elif cpu_choice == choices[1]:
        print("You Win!!! :>>")
    else:
        print("Draw")

Answer 3

Just make your condition literals to lower case:

if player_choice == 'rock':

Answer 4

You can do:

if player_choice.lower() == 'rock'

This will take the user input and lowercase everything in it.

Answer 5

A better way would be to have both player and computer choose from the same set of values. The player enters values until they enter a valid choice. The computer uses random.choice() to select one of the choices from the valid list of choices. Note that you can lower case the possible selections in the valid list:

choices = ["rock", "paper", "scissors"]

Then it is easy to compare the computer and player selections by direct comparision. Here's code for the player and computer choices:

while True:
    player_choice = input("Rock, Paper, Scissors? ").lower()
    if player_choice in choices:
        break
    print("Invalid choice, try again.")

cpu_choice = random.choice(choices)

print()
print("You play:", player_choice)
print("The computer plays:", cpu_choice)
print()

if player_choice == cpu_choice:
    print("Draw")
elif player_choice == 'rock':
    if cpu_choice == 'paper':
        print("You Lose :((")
    else:
        print("You win!! :>>")
elif player_choice == 'paper':
    if cpu_choice == 'scissors':
        print("You Lose :((")
    else:
        print("You win!! :>>")
else:    # player chose scissors
    if cpu_choice == 'rock':
        print("You Lose :((")
    else:
        print("You win!! :>>")