Python/conversions/roman_numerals.py

ROMAN = [
    (1000000, "M_"), (900000, "C_M_"), (500000, "D_"), (400000, "C_D_"),
    (100000, "C_"), (90000, "X_C_"), (50000, "L_"), (40000, "X_L_"),
    (10000, "X_"), (9000, "I_X_"), (5000, "V_"), (4000, "I_V_"),
    (1000, "M"), (900, "CM"), (500, "D"), (400, "CD"),
    (100, "C"), (90, "XC"), (50, "L"), (40, "XL"),
    (10, "X"), (9, "IX"), (5, "V"), (4, "IV"), (1, "I")
]
def roman_to_int(roman):
    vals = {roman: arabic for arabic, roman in ROMAN}
    i, total = 0, 0
    while i < len(roman):
        if i + 1 < len(roman) and roman[i + 1] == "_":
            total += vals[roman[i] + "_"]
            i += 2
        else:
            total += vals[roman[i]]
            i += 1
    return total
def int_to_roman(number):
    if not isinstance(number, int) or number <= 0:
        raise ValueError("Input must be a positive integer greater than 0")

    result = []
    for arabic, roman in ROMAN:
        factor, number = divmod(number, arabic)
        result.append(roman * factor)
        if number == 0:
            break
    return "".join(result)
    
if __name__ == "__main__":
    import doctest
    doctest.testmod()