20. Valid Parentheses - LeetCode

class Solution:
    def isValid(self, s: str) -> bool:
        P = {
            '(': ')',
            '{': '}',
            '[': ']',
        }
        stack = []
        for c in s:
            if stack and P.get(stack[-1]) == c:
                stack.pop()
            else:
                stack.append(c)
        return not stack