roman_numerals.py

ROMANS = (('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 parse_roman_numeral_from_string(s):

    roman_string = str(s)
    n = 0

    for letter, value in ROMANS:
        while letter == roman_string[:len(letter)]:
            n += value
            roman_string = roman_string[len(letter):]
    return n

def parse_roman_numeral_from_int(n):

    roman_int = int(n)
    s = ''

    for letter, value in ROMANS:
        while roman_int >= value:
            s += letter
            roman_int -= value
        if roman_int == 0:
            break
    return s