valid-parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.

Example 1:

Input: "()"
Output: true
Example 2:

Input: "()[]{}"
Output: true
Example 3:

Input: "(]"
Output: false
Example 4:

Input: "([)]"
Output: false
Example 5:

Input: "{[]}"
Output: true

My code:
class Solution:
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        stack=[]
        for i in range(len(s)):
            if s[i]=='(':
                stack.append(s[i])
            if s[i]=='{':
                stack.append(s[i])
            if s[i]=='[':
                stack.append(s[i])
            if s[i]==')':
                if len(stack)==0:
                    return False
                if stack[-1]=='(':
                    stack.pop(-1)
                else:
                    return False
            if s[i]==']':
                if len(stack)==0:
                    return False
                if stack[-1]=='[':
                    stack.pop(-1)
                else:
                    return False
            if s[i]=='}':
                if len(stack)==0:
                    return False
                if stack[-1]=='{':
                    stack.pop(-1)
                else:
                    return False
        if len(stack)==0:
            return True
        else:
            return False
                
        
Solution:
https://leetcode.com/problems/valid-parentheses/