20. valid parentheses

class (object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        left = {'(': 0, '[': 1, '{': 2}    
        right = {')': 0, ']': 1, '}': 2}   # right dict
        stack = []                         # working stack
    
        for i in s:                        # every element in s
            if i in left:                  # if it's one of the lefts
                stack.append(i)            # stack push
            elif i in right:               # if it's one of the rights
                try:                       # try to pop
                    tmp = stack.pop()
                except IndexError:         # if nothing to pop, return False
                    return False
                if left[tmp] != right[i]:  # if they do not match, return False
                    return False
        if stack == []:                    # stack must be empty
            return True
        else:
            return False