Romannumerals2

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

def next_is_combo(numeral, index):
    try:
        if numeral[index] + numeral[index+1] in NUMERALS:
            return True
        else:
            return False
    except IndexError:
        return False

def previous_is_combo(numeral, index):
    if index - 1 < 0:
        return False
    elif numeral[index-1] + numeral[index] in NUMERALS:
        return True
    else:
        return False

def compare(numeral, index):
    if next_is_combo(numeral, index):
        return NUMERALS[numeral[index] + numeral[index+1]]
    elif previous_is_combo(numeral, index):
        return 0
    else:
        return NUMERALS[numeral[index]]

def numeral_to_decimal(numeral):
    decimal = 0

    for letter in range(len(numeral)):
        decimal += compare(numeral, letter)

    return decimal

def main():
    print(numeral_to_decimal("MCMLIV"))
    print()
    print(numeral_to_decimal("MMVIII"))
    print()
    print(numeral_to_decimal("MCMXC"))
    print()
    print(numeral_to_decimal("MCDIV"))

if __name__ == "__main__":
    main()