ordinal_to_roman.py

def ordinal_to_roman(ordinal):
    """
    Converts a chapter ordinal (number, word, or Roman numeral) to a Roman numeral.

    Args:
        ordinal: The chapter ordinal, which can be an integer, a word
                 representation of a number (e.g., "one", "two"), or a
                 Roman numeral string.

    Returns:
        The Roman numeral representation of the ordinal, or None if the
        input cannot be converted.

    Examples:
        ordinal_to_roman(1) == "I"
        ordinal_to_roman("2") == "II"
        ordinal_to_roman("three") == "III"
        ordinal_to_roman("IV") == "IV"
        ordinal_to_roman(5) == "V"
        ordinal_to_roman(10) == "X"
        ordinal_to_roman(15) == "XV"
        ordinal_to_roman(20) == "XX"
        ordinal_to_roman(50) == "L"
        ordinal_to_roman(100) == "C"
        ordinal_to_roman(500) == "D"
        ordinal_to_roman(1000) == "M"
        ordinal_to_roman("one") == "I"
        ordinal_to_roman("two") == "II"
        ordinal_to_roman("three") == "III"
        ordinal_to_roman("four") == "IV"
        ordinal_to_roman("five") == "V"
        ordinal_to_roman("six") == "VI"
        ordinal_to_roman("seven") == "VII"
        ordinal_to_roman("eight") == "VIII"
        ordinal_to_roman("nine") == "IX"
        ordinal_to_roman("ten") == "X"
        ordinal_to_roman(11) == "XI"
        ordinal_to_roman(12) == "XII"
        ordinal_to_roman(13) == "XIII"
        ordinal_to_roman(14) == "XIV"
        ordinal_to_roman(15) == "XV"
        ordinal_to_roman(16) == "XVI"
        ordinal_to_roman(17) == "XVII"
        ordinal_to_roman(18) == "XVIII"
        ordinal_to_roman(19) == "XIX"
        ordinal_to_roman(20) == "XX"
        ordinal_to_roman(21) == "XXI"
        ordinal_to_roman(24) == "XXIV"
        ordinal_to_roman(25) == "XXV"
        ordinal_to_roman(26) == "XXVI"
        ordinal_to_roman(27) == "XXVII"
        ordinal_to_roman(28) == "XXVIII"
        ordinal_to_roman(29) == "XXIX"
        ordinal_to_roman(30) == "XXX"
        ordinal_to_roman(40) == "XL"
        ordinal_to_roman(49) == "XLIX"
        ordinal_to_roman(50) == "L"
        ordinal_to_roman(90) == "XC"
        ordinal_to_roman(99) == "XCIX"
        ordinal_to_roman(100) == "C"
        ordinal_to_roman(400) == "CD"
        ordinal_to_roman(500) == "D"
        ordinal_to_roman(900) == "CM"
        ordinal_to_roman(1000) == "M"
        ordinal_to_roman(1994) == 'MCMXCIV'
        ordinal_to_roman(3999) == 'MMMCMXCIX'
    """
    if not ordinal:
        return None

    # Define the Roman numeral values
    roman_map = {
        1: "I",
        4: "IV",
        5: "V",
        9: "IX",
        10: "X",
        40: "XL",
        50: "L",
        90: "XC",
        100: "C",
        400: "CD",
        500: "D",
        900: "CM",
        1000: "M",
    }

    # Handle integer input
    if isinstance(ordinal, (int, float)):
        try:
            num = int(ordinal)  # Convert float to int if necessary
        except ValueError:
            return None  # Handle invalid numeric input
        if num <= 0 or num > 3999:
            return None  # Roman numerals are not defined for these numbers
    # Handle string input (word or Roman numeral)
    elif isinstance(ordinal, str):
        ordinal = ordinal.strip().lower()  # remove white spaces and convert to lower

        # Try converting word to number
        word_to_num = {
            "one": 1,
            "two": 2,
            "three": 3,
            "four": 4,
            "five": 5,
            "six": 6,
            "seven": 7,
            "eight": 8,
            "nine": 9,
            "ten": 10,
            "eleven": 11,
            "twelve": 12,
            "thirteen": 13,
            "fourteen": 14,
            "fifteen": 15,
            "sixteen": 16,
            "seventeen": 17,
            "eighteen": 18,
            "nineteen": 19,
            "twenty": 20,
            "thirty": 30,
            "forty": 40,
            "fifty": 50,
            "sixty": 60,
            "seventy": 70,
            "eighty": 80,
            "ninety": 90,
            "hundred": 100,
            "thousand": 1000,
        }
        if ordinal in word_to_num:
            num = word_to_num[ordinal]
        else:
            # Attempt to convert from Roman numeral string to integer
            roman_numeral_map = {
                "I": 1,
                "V": 5,
                "X": 10,
                "L": 50,
                "C": 100,
                "D": 500,
                "M": 1000,
            }
            i = 0
            number = 0
            while i < len(ordinal):
                char = ordinal[i]
                if char not in roman_numeral_map:
                    return None
                val = roman_numeral_map[char]
                if i + 1 < len(ordinal):
                    next_char = ordinal[i + 1]
                    next_val = roman_numeral_map[next_char]
                    if val < next_val:
                        number += next_val - val
                        i += 2
                    else:
                        number += val
                        i += 1
                else:
                    number += val
                    i += 1
            num = number

    else:
        return None

    if num <= 0 or num > 3999:
        return None  # Roman numerals are not defined for these numbers

    # Convert the number to a Roman numeral
    result = ""
    values = sorted(roman_map.keys(), reverse=True)
    for value in values:
        while num >= value:
            result += roman_map[value]
            num -= value
    return result