Leetcode-Easy 20. Valid Parentheses

class Solution:
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        dict={"()","[]","{}"}
        arr=[]
        for i in range(len(s)):
            if len(arr)!=0 and (arr[-1]+s[i]) in dict:
                arr.pop()
            else:
                arr.append(s[i])
        return len(arr)==0