在python中将罗马数字转换为整数

Question

这是user2486所说的之后的当前代码。

def romanMap():
    map=(("M",  1000),("CM", 900),("D",  500),("CD", 400),("C",  100),("XC", 90),("L",  50),("XL", 40),("X",  10),("IX", 9),("V",  5),("V", 4),("I",  1))
    return map
firstNum=ns([0])
secondNum=ns([1])
def main():
    ns=str(input("Enter a roman numeral"))
    total=0
    result=0
    while ns:
        firstNum=(romanMap(ns[0]))
         secondNum=(romanMap(ns[1]) 
        if firstNum is len(ns)>1 or secondNum-1:
                        total=total+firstNum
            ns=ns[1:]
        else:
                        total=total+ns[1]-ns[0]
            ns=ns[2:]
      print (total)
main()

我在使用ns时遇到此错误：UnboundLocalError：分配前引用了本地变量’ns’

Answer 1

考虑一下此附加的伪代码和提示（其中一些是有效的Python，一些不是有效的，但有注释）。

def numberOfNumeral(n):
    """ Return the number represented by the single numeral """
    # e.g. "v" -> 5, "i" -> 5 (and handle v/V cases, etc.)

# avoid "string" as a variable name
# I chose "ns" for "numerals" (which might be better),
# but I'm also a bit terse .. anyway, name variables for what they represents.
ns = str(input("Enter a roman numeral"))

while ns:
   firstNum = numberOfNumeral(ns[0])
   # This makes secondValue = -1 when there is only one numeral left
   # so firstNum is always "at least" secondNum when len(ns) == 1. 
   secondNum = numberOfNumeral(ns[1]) if len(ns) > 1 else -1
   if firstNum is at least secondNum:
      # Add firstNum to total.
      # Remove the character - so that the loop state advances.
      # If we don't don't his, as in the original, it will never end.
      # Here we use "slice notation".
      ns = ns[1:] 
   else:
      # Add the difference, secondNum - firstNum, to total.
      # Remove both characters - again, so we advance state.
      ns = ns[2:]