如何获得我的函数来区分python中的输入“ I”和“ II”？

Question

我的目标是让用户在I和V之间输入两个罗马数字并将它们加在一起。我想用十进制值和它们的罗马数字等价形式显示等式。

但是，当我输入I和V以外的值时，该值将被分配为'NoneType'，并且程序将失败。我试过将返回值设置为str（），然后再调用int（），将罗马num设置为''：num_value =＃，然后在最后返回num_value，但没有一个起作用。

我认为我缺少了一些非常基本的东西，这与区分具有重复字符的值有关，例如'I'（可以）和'II'，后者被分配了NoneType。

firstNumeral = input("please enter a roman numeral between I and V: ")
secondNumeral = input('please enter a second roman numeral between I and V: ')
def get_user_num(roman_num):
    if roman_num is 'I':
        return int(1)
    elif roman_num is 'II':
        return int(2)
    elif roman_num is 'III':
        return int(3)
    elif roman_num is 'IV':
        return int(4)
    elif roman_num is 'V':
        return int(5)
    elif roman_num is 'VI':
        return int(6)
    elif roman_num is 'VII':
        return int(7)
    elif roman_num is 'VIII':
        return int(8)
    elif roman_num is 'IX':
        return int(9)
    elif roman_num is 'X':
        return int(10)
firstNumber = get_user_num(firstNumeral)
secondNumber = get_user_num(secondNumeral)
totalNumber = firstNumber + secondNumber
def get_roman_number(result_number):
    if result_number == 1:
        return "I"
    elif result_number == 2:
        return "II"
    elif result_number == 3:
        return 'III'
    elif result_number == 4:
        return 'IV'
    elif result_number == 5:
        return 'V'
    elif result_number == 6:
        return 'VI'
    elif result_number == 7:
        return 'VII'
    elif result_number == 8:
        return 'VIII'
    elif result_number == 9:
        return 'IX'
    elif result_number == 10:
        return 'X'
totalNumeral = get_roman_number(totalNumber)
print('Decimal values {} + {} = {}'.format(firstNumber,secondNumber, totalNumber))
print('Roman Numeral values {} + {} = {}'.format(firstNumeral, secondNumeral, totalNumeral))

当使用I和V以外的任何其他值时，我会得到

Traceback (most recent call last):
  File ... line 26, in <module>
    totalNumber = firstNumber + secondNumber
TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'''

Answer 1

firstNumeral = input("please enter a roman numeral between I and V: ")
secondNumeral = input('please enter a second roman numeral between I and V: ')
def get_user_num(roman_num):
    if roman_num is 'I':
        return int(1)
    elif roman_num == 'II':
        return int(2)
    elif roman_num == 'III':
        return int(3)
    elif roman_num == 'IV':
        return int(4)
    elif roman_num == 'V':
        return int(5)
    elif roman_num is 'VI':
        return int(6)
    elif roman_num == 'VII':
        return int(7)
    elif roman_num == 'VIII':
        return int(8)
    elif roman_num == 'IX':
        return int(9)
    elif roman_num == 'X':
        return int(10)
firstNumber = get_user_num(firstNumeral)
secondNumber = get_user_num(secondNumeral)
print(secondNumber)
totalNumber = firstNumber + secondNumber
def get_roman_number(result_number):
    if result_number == 1:
        return "I"
    elif result_number == 2:
        return "II"
    elif result_number == 3:
        return 'III'
    elif result_number == 4:
        return 'IV'
    elif result_number == 5:
        return 'V'
    elif result_number == 6:
        return 'VI'
    elif result_number == 7:
        return 'VII'
    elif result_number == 8:
        return 'VIII'
    elif result_number == 9:
        return 'IX'
    elif result_number == 10:
        return 'X'
totalNumeral = get_roman_number(totalNumber)
print('Decimal values {} + {} = {}'.format(firstNumber,secondNumber, totalNumber))
print('Roman Numeral values {} + {} = {}'.format(firstNumeral, secondNumeral, totalNumeral))

使用'=='检查条件