This is an attempt at making the most concise roman numeral "solver" possible using recursivity.

roman_numerals.py

import sys

from numpy import argmax

translate = {
    'I': 1,
    'V': 5,
    'X': 10,
    'L': 50,
    'C': 100,
    'D': 500,
    'M': 1000
}


def is_valid(sequence):
    """ Checks that a sequence of numbers is valid according
        to the rules of Roman numeral notation.
        Is incomplete, accepts some invalid numbers.
        Args:
            sequence (list<int>): a Roman numeral but with each letter
                replaced by its arabic numeral counterpart.
        Returns:
            valid (bool): whether the Roman numeral is valid or not
    """
    for i in range(1, len(sequence)):
        if sequence[i] / sequence[i - 1] > 10:
            return False
    return True


def solve(sequence):
    """ Converts a Roman numeral to a traditional integer.
        Args:
            sequence (list<int>): a Roman numeral but with each letter
                replaced by its arabic numeral counterpart.
        Returns:
            number (int): the number represented by the Roman numeral
    """
    if len(sequence) == 0:
        return 0
    pivot = argmax(sequence)
    number = (sequence[pivot] +
              solve(sequence[pivot + 1:]) -
              solve(sequence[:pivot]))
    return number


if __name__ == '__main__':
    roman = sys.argv[1]
    arab = [translate[i] for i in roman]
    assert is_valid(arab)
    print(solve(arab))

This code is released under the .