roman to integer

class (object):
    def romanToInt(self, s):
        """
        :type s: str
        :rtype: int
        """
        
        #	    I	V	X	L	C	D	M
        #	    1	5	10	50	100	500	1,000
        # special cases
        #Number	4	9	40	90	400	900
        #Note	IV	IX	XL	XC	CD	CM
        
        number = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1]
        symbol = ["M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"]
        n = 0
        i = 0
        while i < len(s):
            if s[i:i+2] in symbol:
                index = symbol.index(s[i:i+2])
                n += number[index]
                i += 2
            else:
                index = symbol.index(s[i])
                n += number[index]
                i += 1
        return n