Longest palindromic substring in quadratic time O(n^2)

longest_palindromic_substring.py

def longestPalindrome(self, s):
    """
    :type s: str
    :rtype: str
    """
    best_palindrome_length = 1
    best_palindrome = s[0]

    n = len(s)
    for i in range(2 * n - 1):
        if i % 2 == 0:
            candidate_string = s[i/2]
            left = i / 2 - 1
            right = i / 2 + 1
        else:
            candidate_string = ''
            left = i / 2
            right = i / 2 + 1
        while left >= 0 and right < n and s[left] == s[right]:
                candidate_string = s[left] + candidate_string + s[right]
                left -= 1
                right += 1
        if len(candidate_string) > best_palindrome_length:
            best_palindrome = candidate_string
            best_palindrome_length = len(candidate_string)

    return best_palindrome