leetcode 20. 有效的括号

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        check=[]
        if len(s)%2==1:
            return False
        for i in range(0,len(s)):
            if len(check)>0:
                if (check[top]=='{' and s[i] == '}') or (check[top]=='(' and s[i] == ')') or (check[top]=='[' and s[i] == ']'):
                     top=len(check)-1
                    del check[top]
                else:
                    check.append(s[i])
            else:
                check.append(s[i])
        if len(check)==0:
            return True
        else:
            return False