Why does my code not work when the given input exceeds 2 digits?

Magically, I still don’t know how removing i fixed everything. But it did.

romanD = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
oper = []
s = input('roman')


class Solution(object):
    def romanToInt(self, s):
        rtype = int
        for j in range(len(s)):
            if j+1 >= len(s):
                break
            elif romanD[s[j]] < romanD[s[j+1]]:
                oper.append(-1 * romanD[s[j]])
            elif romanD[s[j]] >= romanD[s[j+1]]:
                oper.append(romanD[s[j]])
        oper.append(romanD[s[len(s) - 1]])
        return sum(oper)


b = Solution()
print(b.romanToInt(s))

This happens because i = 0 is in the for j in range() loop, so i will always be 0. To fix this just put i = 0 before the loop like this:

def romanToInt(self, s):
        rtype = int
        # for i in range(len(s)-1):
        i = 0  # <---- here :)
        for j in range(1, len(s)):
            if i >= len(s):
                break
            elif romanD[s[i]] < romanD[s[j]]:
                oper.append(-1 * romanD[s[i]])
            elif romanD[s[i]] >= romanD[s[j]]:
                oper.append(romanD[s[i]])
            i += 1
        oper.append(romanD[s[len(s) - 1]])
        return sum(oper)