Leetcode 005 Longest Palindromic Substring

def longestPalindrome(self, s: str) -> str:
        longest = ''
        def findLongest(s, l, r):
            while l>=0 and r<len(s) and s[l] == s[r]:
                l-=1
                r+=1
            return s[l+1:r]
        
        for i in range(len(s)):
            # odd case, like "aba"
            s1 = findLongest(s, i, i)
            if len(s1) > len(longest): longest = s1
            # even case, like "abba"
            s2 = findLongest(s, i, i+1)
            if len(s2) > len(longest): longest = s2
                
        return longest