# -*- coding: utf-8 -*-

roman_numerals = zip((1000, 900,  500, 400, 100,  90, 50,  40, 10,  9,   5,  4,   1),
                     ('M',  'CM', 'D', 'CD','C', 'XC','L','XL','X','IX','V','IV','I'))

def roman(num):
    res = ""
    for i, n in roman_numerals:
        res += n * (num // i)
        num %= i
    return res

def from_roman(rom):
    if not rom:
        return 0
    for i, n in roman_numerals:
        if rom.upper().startswith(n):
            return i + from_roman(rom[len(n):])
    raise Exception('Invalid roman numeral: "%s"', rom)