32. Longest Valid Parentheses leetcode python new season 2016

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

For "(()", the longest valid parentheses substring is "()", which has length = 2.

Another example is ")()())", where the longest valid parentheses substring is "()()", which has length = 4.

class Solution(object):
    def longestValidParentheses(self, s):
        """
        :type s: str
        :rtype: int
        """
        s = ')' + s
        stack, result = [], 0
        for index in range(len(s)):
            element = s[index]
            if element == ')' and stack and stack[-1][1] == '(':
                stack.pop()
                result = max(result, index - stack[-1][0])
            else:
                stack.append((index, s[index]))
        return result