valid-parenthesis.py

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """

        stack = []

        closeToOpen = {
            ")" : "(",
            "]": "[",
            "}": "{"
        }

        for c in s:
            if c in closeToOpen:
                if stack and stack[-1] == closeToOpen[c]:
                    stack.pop()
                else:
                    return False
            else:
                stack.append(c)
        return len(stack) == 0