Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.

Strings in Python are immutable (can't be changed). Because of this, the effect of line.replace(...) is just to create a new string, rather than changing the old one. You need to rebind (assign) it to line in order to have that variable take the new value, with those characters removed.

class Solution(object):
    def romanToInt(self, s):
        """
        :type s: str
        :rtype: int
        """
        roman = {'I':1, 'V':5, 'X':10,'L':50,'C':100,'D':500,'M':1000}
        sub = {'IV':4,'IX':9,'XL':40,'XC':90,'CD':400,'CM':900}
        ans = 0
        ss = [s]
        for key in sub:
            if key in s:
                ans += sub[key]
                new = ss.pop()
                ss.append(new.replace(key, ''))
        sss = ss.pop()
        for c in sss:
            ans += roman[c]
        return ans