问如何用以下逻辑在python中为罗马数字到整数转换编写代码

EN

def roman_numeral(num):
    """
    Write a Python class to convert an roman numeral to a integer.
    Logic: https://www.rapidtables.com/convert/number/how-roman-numerals-to-number.html
    """
    # Input the string 
    # Map of roman numerals and the corresponding values in a dictionary.
    NUMERALS = {1000:'M', 900:'CM', 500:'D', 400:'CD', 100:'C', 90:'XC',
                50:'L', 40:'XL', 10:'X', 9:'IX', 5:'V', 4:'IV', 1:'I'}
    retval=[]
     
    #Check if each char matches with the dictionary and take the numerical value of the inputed roman 
     
    for k in range(len(num)):
        for i,j in NUMERALS.items():
            if(j==num[k]):
                retval.append(i)

    elm_count = len(retval)       
    result=0 
    result_less=0
    result_more=0
    # ind_tracker=0
    flag = False
    
    #Check if next char from the position of current char if that numerical value is greater then current numerical value.
    #If it is greater subtract the current numeric value, if not greater then add it.   

    for ind,i in enumerate(retval):
        print('ind= ',ind,'i= ', i)
        #Using this below condition to skip if we have already subtracted the current value from previous value.
        # if( ind_tracker>ind):
        #     continue
        
        if(flag):
          print("Skipped! Already Subracted!")
          flag=False
          continue
        
        if((ind+1 == elm_count)):
          # if last digit is greater than it's previous, the flag will skip this iteration
          print('last digit=',retval[ind])   
           result+=retval[ind]
        
        if((ind+1 < elm_count)):
                if(i<retval[ind+1]):
                    #print('result=',result,'retval[ind]=',retval[ind],'retval[ind+1]=', retval[ind+1])
                    # result_less=retval[ind+1]-retval[ind]
                    result+=retval[ind+1]-retval[ind]
                    print('result_less=',retval[ind+1]-retval[ind])
                    # ind_tracker=ind+1
                    flag = True
                else:
                    # result_more+=retval[ind]+result_less
                    result+=retval[ind]
                    print('result_more=',retval[ind])            
                    # result=result_more   
    
    print('final result= ',result)    
    return result

roman_numeral('MCMXCVI')

class RomanToDecimal:
    conversion = {'M': 1000, 'CM': 900, 'D': 500, 'CD': 400, 'C': 100, 'XC': 90, 'L': 50, 'XL': 40, 'X': 10, 'IX': 9,
                  'V': 5, 'IV': 4, 'I': 1}

    def convert(self, roman):
        total = 0
        while len(roman):
            before = len(roman)
            for key in self.conversion:
                if roman.startswith(key):
                    total += self.conversion[key]
                    roman = roman[len(key):]
            after = len(roman)
            if before == after:
                raise ValueError("Not a Roman numeral.")
        return total

try:
    rtd = RomanToDecimal()
    assert rtd.convert('M') == 1000
    assert rtd.convert('XXXVI') == 36
    assert rtd.convert('MMXII') == 2012
    assert rtd.convert('MMXX') == 2020
except ValueError as error:
    print(error)

roman = "MCMXCVI"

NUMERALS = {1000:'M', 900:'CM', 500:'D', 400:'CD', 100:'C', 90:'XC',
                50:'L', 40:'XL', 10:'X', 9:'IX', 5:'V', 4:'IV', 1:'I'}

# reverse roman number letters (basically start from the end
roman_reversed = list(reversed(roman))
#invert the dictionary because we want to translate the letter to numbers not the other way around
inverse_NUMERALS = {v: k for k, v in NUMERALS.items()}

# get the number for each character on its own:
lst_numbers = [inverse_NUMERALS.get(x) for x in roman_reversed]


# loop through the list of numbers
total = 0
previous = 0
for numb in lst_numbers:
    if numb >= previous:
        total += numb
    else:
        total -= numb
    previous = numb
    
print(total)
#Out[21]: 1996