Numbers to Roman Numerals

Numbers to Roman Numerals

import unittest

KNOWN_VALUES = [
    (1, 'I'),
    (5, 'V'),
    (10,'X'),
    (50,'L'),
    (100,'C'),
    (500,'D'),
    (1000,'M'),
    
    (2, "II"),
    (3, "III"),
    (4, "IV"),
    
    (200,"CC"),
    
    (9, "IX"),
    
    (207, "CCVII"),
    (1904, "MCMIV"),
    (1954, "MCMLIV"),
    (2013, "MMXIII"),
    (400, "CD"),
    (900, "CM"),
    (10000, "MMMMMMMMMM"),
    ]



SYMBOLS = [
    (1, 'I'),
    (5, 'V'),
    (10,'X'),
    (50,'L'),
    (100,'C'),
    (500,'D'),
    (1000,'M'),
    ]

def convert(number):
    big_string = number*'I'
    
    
    return big_string_to_small(big_string)

def big_string_to_small(big_string):
    """
    >>> big_string_to_small('I'*1000)
    'M'
    >>> big_string_to_small('I'*500)
    'D'
    >>> big_string_to_small('I'*100)
    'C'
    >>> big_string_to_small('I'*105)
    'CV'
    """
    result = big_string
    for (number, text) in reversed(SYMBOLS):
        if number*'I' in result:
            # Replace all runs of "I" with the appropriate symbol
            result = result.replace(number*'I',text)
    #print result
    return replace_repeats(result)

def replace_repeats(roman):
    """
    >>> replace_repeats('IIII')
    'IV'
    >>> replace_repeats('XXXX')
    'XL'
    >>> replace_repeats(convert(404))
    'CDIV'
    """
    result = roman
    for (_, smaller), (_, bigger) in zip(SYMBOLS, SYMBOLS[1:]):
        if 4*smaller in result:
            target = "{}{}".format(smaller, bigger)
            result = result.replace(4*smaller, target)
    return result


class KnownGood(unittest.TestCase):
    def __init__(self, input, output):
        super(KnownGood, self).__init__()
        self.input = input
        self.output = output
        
    def runTest(self):
        self.assertEqual(convert(self.input), self.output)


def make_suite():
    suite = unittest.TestSuite()
    suite.addTests(KnownGood(input, output) for input, output in KNOWN_VALUES)
    return suite
    
if __name__ == '__main__':
    unittest.TextTestRunner().run(make_suite())