Roman number to Integer. Very efficient with Time and Space complexity

Roman_Integer.py

#This solution works only when executed on LeetCode. For test cases and practice, check my git repo
class Solution:
    def romanToInt(self, s: str) -> int:
        Guide = {'I':1, 'V':5, 'X':10, 'L':50, 'C':100, 'D': 500, 'M':1000}
        num = prev_char = 0
        for char in s[::-1]:
            if Guide[char] >= prev_char:
                prev_char = Guide[char]
                num = num + Guide[char]
            else:
                num = num - Guide[char]
        return(num)