括号序列的python实现

#
# 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可
#
# 
# @param s string字符串 
# @return bool布尔型
#
class Solution:
    def isValid(self , s: str) -> bool:
        # write code here
        dic = {'(':')', '{': '}', '[':']', '?':'?'}
        mystack = ['?']
        for c in s:
            if c in dic: mystack.append(c)
            elif dic[mystack.pop()]!=c: return False
        return len(mystack)==1