如何使用break语句

Question

我在2.7中有一个正常工作的货币转换器，但我想确保该程序不会获取用户无法处理的数据。如何获得与案例无关的用户输入如果用户输入错误，如何使程序重新启动；即休息一下，但是尽管四处寻找并测试了一些方法，但我仍无法弄清楚该如何做。我保留了其余的代码，因为它与使用预设数字的第一组乘法实际上无关紧要。currency = str(raw_input ("""what currency would you like to covert: GBP, EURO, USD OR YEN?"""))exchange = str(raw_input("""what currency would you like in exchange? : GBP, EURO, USD OR YEN?                              """))amount = int(input("""how much would you like to convert?                      """))decision = str(raw_input("""Please enter u for user input exchange rate or s for the preset exchange rate"""))if decision == "u" :    user_rate = raw_input("Please enter the current exchange rate")    exchange_value = int(amount) *  int(user_rate)    print ("At the user found exchange rate you will receive",exchange_value,exchange)elif decision == "s" :    if currency  == "GBP" and exchange == "USD":        exchange_value= int(amount) * 1.6048        print ("At the preset exchange rate you will receive",exchange_value,exchange)    if currency  == "GBP" and exchange == "EUR":        exchange_value= int(amount) * 1.2399        print ("At the preset exchange rate you will receive",exchange_value,exchange)

Answer 1

这样的事情将帮助您入门

    valid_input = ('EUR', 'GBP', 'USD', 'JPY')

    while True:

        # Obtain user data

        # Make sure all its in caps

        currency = currency.upper()

        exchange = exchange.upper()

        if currency in valid_input and exchange in valid_input:

            break 

         print ("Error Invalid input, try again...")

    # Proccess data...

Answer 2

1）您可以使用相同的大小写来比较用户输入的字符串

if currency.lower() == 'gbp'

或者

if currency.upper() == 'GBP'

2）您可以在while循环中运行程序，这样，如果不满足条件，则可以continue循环到下一次迭代（这将从头开始重新启动程序）

while True:

  # get user input

  # validate user input

  # if input not valid continue, which will "restart" your program