Longest Palindrome in String

leetcode:"https://www.geeksforgeeks.org/must-do-coding-questions-for-companies-like-amazon-microsoft-adobe/#string"
class Solution:
    def longestPalindrome(self, s: str) -> str:
        n,l,r,res,ret=len(s),0,0,0,""

        for i in range(n):
            #for odd length
            l=r=i
            while l>=0 and r<n and s[l]==s[r]:
                if res<r-l+1:
                    res=r-l+1
                    ret=s[l:r+1]
                l,r=l-1,r+1
            #for even lentgh
            l,r=i,i+1
            while l>=0 and r<n and s[l]==s[r]:
                if res<r-l+1:
                    res=r-l+1
                    ret=s[l:r+1]
                l,r=l-1,r+1
        return ret