python - 我希望在要求用户再次输入内容之前弹出一个错误

Question

在上面的代码中，当我按下任何其他键时，我希望在返回 user_input 之前弹出一条错误消息。请帮助某人？

Answer 1

while在循环结束时检查它是否有效：

currencies = ['pound', 'euro', 'dollar', 'yen', '$', '£', '¥','€']

def get_currency(msg):
    while True:
        user_input = input(msg).lower()

        if user_input not in currencies:
            print('Invalid currency')
        else:
            return user_input

Answer 2

# -*- coding: utf-8 -*-
valid = ['pound', 'euro', 'dollar', 'yen', '$', '£', '¥','€']
msg="Enter currency: "
def get_currency(msg):

    input_valid = input(msg).lower()

    while input_valid not in valid:       #run this loop until the input is not valid
        print ("Invalid Input, Try again")  #the error message
        input_valid = input(msg).lower()

    return input_valid

print (get_currency(msg))

输出：

~$ python3 so.py
Enter currency: foo
Invalid Input, Try again
Enter currency: bar
Invalid Input, Try again
Enter currency: pound
pound