numbers_to_roman.py

def number_to_roman(number):
    """Convert a number between 1 and 3,999,999 to roman numerals."""

    ROMAN_ONES = ['I', 'X', 'C', 'M', 'X̅', 'C̅', 'M̅']
    ROMAN_FIVES = ['V', 'L', 'D', 'V̅', 'L̅', 'D̅']
    conversion = ""

    if not str(number).isnumeric():
        return "Only numbers are allowed."

    if int(number) > 3999999:
        return "Please enter a number lower than 3,999,999."

    for index, number in enumerate(str(number)[::-1]):
        number = int(number)
        if number in range(1, 4):
            conversion += ROMAN_ONES[index] * number
        elif number == 4:
            conversion += ROMAN_FIVES[index] + ROMAN_ONES[index]
        elif number == 5:
            conversion += ROMAN_FIVES[index]
        elif number in range(6, 9):
            conversion += ROMAN_ONES[index] * (number % 5) + ROMAN_FIVES[index]
        elif number == 9:
            conversion += ROMAN_ONES[index + 1] + ROMAN_ONES[index]

    return conversion[::-1]

if __name__ == '__main__':
    number = input('Enter a number: ')
    print(number_to_roman(number))