Valid Parentheses

class Solution(object):
    def isValid(self, s):
        stack = [] # create an empty stack to store opening brackets
        for c in s: # loop through each character in the string
            if c in '([{': # if the character is an opening bracket
                stack.append(c) # push it onto the stack
            else: # if the character is a closing bracket
                if not stack or \
                    (c == ')' and stack[-1] != '(') or \
                    (c == '}' and stack[-1] != '{') or \
                    (c == ']' and stack[-1] != '['):
                    return False # the string is not valid, so return false
                stack.pop() # otherwise, pop the opening bracket from the stack
        return not stack # if the stack is empty, all opening brackets have been matched with their corresponding closing brackets,
                         # so the string is valid, otherwise, there are unmatched opening brackets, so return false