如何让我的函数在 python 中区分输入 '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相加。我想以十进制值及其等价的罗马数字显示方程式。

但是，每当我输入 I 和 V 以外的值时，该值都会被分配 'NoneType'，并且程序会失败。我试过将 returns 设置为 str() 然后稍后调用 int() ，设置 roman num 是 '': num_value = # 然后在最后返回 num_value ，但是none 成功了。

我想我遗漏了一些非常基本的东西，它与区分具有重复字符的值有关，例如 'I' （没问题）和 'II' 被分配 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 以外的任何值时，我得到

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

Answer 2

您的 get_user_num(roman_num) 函数有一些问题，如前所述，您需要使用“==”而不是 is。

此外，您没有故障保护装置，因此如果用户输入非法内容，None 将被 returned，这会破坏您的代码。一个快速解决这个问题的方法是在函数末尾添加 return get_user_num(input("please enter a roman numeral between I and V: ")) 行：

def get_user_num(roman_num):
    if roman_num == 'I':
        return int(1)
    if roman_num == 'II':
        return int(2)
    if roman_num == 'III':
        return int(3)
    if roman_num == 'IV':
        return int(4)
    if roman_num == 'V':
        return int(5)
    if roman_num == 'VI':
        return int(6)
    if roman_num == 'VII':
        return int(7)
    if roman_num == 'VIII':
        return int(8)
    if roman_num == 'IX':
        return int(9)
    if roman_num == 'X':
        return int(10)
    return get_user_num(input("please enter a roman numeral between I and V: "))

您也可以使用 if 而不是 elif，因为如果满足任何条件，该函数将 return。不过，如果您计划扩展到 10 以上，我建议采用更简洁的方法和更强大的算法。

如何让我的函数在 python 中区分输入 'I' 和 'II'？

How do I get my function to differentiate between input 'I' and 'II' in python?

python-3.x

roman-numerals