Converting Roman Numerals into Arabic numbers

roman_to_arabic.py

def convert(numeral):
    romans = {
        "I": 1,
        "V": 5,
        "X": 10,
        "L": 50,
        "C": 100,
        "D": 500,
        "M": 1000
    }
    arabic = []
    total = 0

    # Convert the Roman Numerals to their Arabic equivalent
    # "VII" would become [5, 1, 1]
    for letter in numeral:
        arabic.append(romans[letter])

    # Cycle through the list backwards. Read Numerals Right-to-Left.
    # [5, 1, 1]
    for k in range(len(arabic))[::-1]:
        if k == len(arabic) - 1:
            total += arabic[k]
            prev = arabic[k]
            continue
        else:
            if arabic[k] >= prev:
                # If the current number is greater/equal to the previous
                # We add it to the total
                total += arabic[k]
            else:
                # Otherwise, if it's less, we subtract.
                total -= arabic[k]
            prev = arabic[k]
    return total


def main():
    _input = {
        "I": 1,
        "IV": 4,
        "VI": 6,
        "IX": 9,
        "CD": 400,
        "III": 3,
        "VIII": 8,
        "CCXXXIX": 239,
        "MCMXCIV": 1994,
        "MMMMCMXCIX": 4999
    }
    for i in _input:
        total = convert(i)
        print("ROAMN: {}\nARABIC: {}\nEXPECTED: {}\n----".format(i, total, _input[i]))


if __name__ == '__main__':
    main()

$ python roman_to_arabic.py
ROAMN: IX
ARABIC: 9
EXPECTED: 9
----
ROAMN: VIII
ARABIC: 8
EXPECTED: 8
----
ROAMN: MCMXCIV
ARABIC: 1994
EXPECTED: 1994
----
ROAMN: I
ARABIC: 1
EXPECTED: 1
----
ROAMN: VI
ARABIC: 6
EXPECTED: 6
----
ROAMN: MMMMCMXCIX
ARABIC: 4999
EXPECTED: 4999
----
ROAMN: CD
ARABIC: 400
EXPECTED: 400
----
ROAMN: III
ARABIC: 3
EXPECTED: 3
----
ROAMN: CCXXXIX
ARABIC: 239
EXPECTED: 239
----
ROAMN: IV
ARABIC: 4
EXPECTED: 4
----