Roman Numerals

roman.py

order = 'MDCLXVI'
add_to_sub = (
    ('VIIII', 'IX'),
    ('LXXXX', 'XC'),
    ('DCCCC', 'CM'),
    ('IIII', 'IV'),
    ('XXXX', 'XL'),
    ('CCCC', 'CD'),
)

sub_to_add = (
    ('IX', 'VIIII'),
    ('IV', 'IIII'),
    ('XC', 'LXXXX'),
    ('XL', 'XXXX'),
    ('CM', 'DCCCC'),
    ('CD', 'CCCC'),
)

pairs = (
    ('IIIII', 'V'),
    ('VV', 'X'),
    ('XXXXX', 'L'),
    ('LL', 'C'),
    ('CCCCC', 'D'),
    ('DD', 'M'),
)
 
roman_value = {
    'I': 1,
    'V': 5,
    'X': 10,
    'L': 50,
    'C': 100,
    'D': 500,
    'M': 1000,
}

def sort_roman(input):
    return ''.join(sorted(input, key=order.index))


def replace_roman(input, replace):
    for key, value in replace:
        input = input.replace(key, value)
    return input

def add_roman(number_one, number_two, debug=False):
    number_one = replace_roman(number_one, sub_to_add)
    number_two = replace_roman(number_two, sub_to_add)


    result = number_one + number_two
    result = sort_roman(result)

    if debug:
        print result, convert_from_roman(result)

    result = replace_roman(result, pairs)

    if debug:
        print result, convert_from_roman(result)

    result = replace_roman(result, add_to_sub)
    
    return result

def convert_to_roman(input):
    result = 'I' * input
    result = replace_roman(result, pairs)
    result = replace_roman(result, add_to_sub)
    return result
    
def convert_from_roman(input):
    input = replace_roman(input, sub_to_add)
    value = 0
    for char in input:
        value += roman_value[char]
    return value

def test(i, j):
    try:
        for a in range(1, i + 1):
            for b in range(1, j + 1):
                a_r = convert_to_roman(a)
                b_r = convert_to_roman(b)
                c_r = add_roman(a_r, b_r)
                c = convert_from_roman(c_r)
                
                assert a + b == c
    except AssertionError:
        print "%d + %d = %d, %s + %s = %s" % (a, b, c, a_r, b_r, c_r)
    

if __name__ == '__main__':
    #result = add_roman("MDXIV", "MMXIV")
    #print result, convert_from_roman(result)

    a = 'CD'
    b = 'M'
    result = add_roman(a, b, debug=True)
    print result, convert_from_roman(result)

    test(2000, 1000)