在python中输入数据不正确时给出用户错误消息

Question

仅以Python货币currencies使用5个converter tool––(USD, EUR, CAD, GBP, and CHF)。如果用户在convertFrom or convertTo中输入其他货币，如何添加错误消息通知用户try again？

转化

convertFrom = input("What currency would you like to convert from? ")

amount = int(input("How much of that currency would you like to convert? "))

convertTo = input("Which currency would you like to convert to? ")

Answer 1

您可以使用有效货币列表

validCurrencies = ["EUR","GBP","USD","CAD", "CHF"]

然后您可以通过

验证输入

currencyFrom = ""

while not currencyFrom in validCurrencies:
  currencyFrom = input("What currency would you like to convert from: (e.g. GBP)").upper()
  if not currencyFrom in validCurrencies:
    print("Invalid Currency, Please Try again")
print("correct Currency please follow next instructions")

输出：

What currency would you like to convert from: (e.g. GBP) uuu
Invalid Currency, Please Try again
What currency would you like to convert from: (e.g. GBP) Gbp
correct Currency please follow next instructions

您可以对convertTo和amount进行相同操作

Answer 2

创建程序支持的货币列表。

当用户输入货币时，在进行转换之前，请检查列表中是否存在该货币。如果不是，则显示错误消息。否则，请继续进行转换

supported_currencies = ['USD', ...]
convertFrom = input("What currency would you like to convert from? ")
    convert()
else:
     print("currency not supported")

您还可以检查convertTo变量是否在受支持的货币列表中。