Arabic -> Roman Numeral

talk open source
1

A while ago, I posted part of this source code, which would calculate the decimal value of Roman numerals. So, I got inspired, and added the much more challenging Arabic to Roman version.

I spent like four hours on this… grr.

def arabic_to_roman(number):
    roman = {1: 'I', 5: 'V', 10: 'X', 50: 'L', 100: 'C', 500: 'D', 1000: 'M'}
    values = roman.keys()
    values.sort()
    
    for value in values[:-1]:
            next = values[values.index(value) + 1]
            if number%next is not 0 and number%next is not 4:
                return arabic_to_roman(number-(number%next))+(roman[value]*(number%next/value))
            elif number%next is 4:
                return roman[value]*(next-(number%next))+arabic_to_roman(next+number-number%next)
    return roman[1000]*(number/1000)


def roman_to_arabic(numerals):
    total = 0
    values = {
        'I': 1,
        'V': 5,
        'X': 10,
        'L': 50,
        'C': 100,
        'D': 500,
        'M': 1000
    }
    
    prev_value = 0
    for char in numerals:
        if values[char] > prev_value:
            total -= prev_value
        else:
            total += prev_value
        prev_value = values[char]
    total += prev_value
    
    return total


if __name__ == '__main__':
    for i in range(10000):
        if i!=roman_to_arabic(arabic_to_roman(i)):
            print i