Convert integers to roman and vice-versa

roman_numerals.py

import re


numerals = {"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}
r = re.compile('|'.join(sorted(numerals.keys(), key=len, reverse=True)))


def to_roman(n, s=''):
    for num, val in numerals.items():
        if n // val:
            n -= val
            s += num
            return to_roman(n, s)
    if not n:
        return s


def to_int(s):
    tokens = r.findall(s)
    return sum(numerals[t] for t in tokens)