Leetcode: Integer to Roman @Python

class Solution:
    # @return a string
    def intToRoman(self, num):
        roman_numeral_map = (('M',  1000),('CM', 900),('D',  500),('CD', 400),('C',  100),('XC', 90),('L',  50),('XL', 40),('X',  10),('IX', 9),('V',  5),('IV', 4),('I',  1))
        rst=''
        for roman, numeral in roman_numeral_map:
            while num>=numeral:
                num-=numeral
                rst+=roman
        return rst