Given a string, if it is a palindrome string, return the string, otherwise add the string to become a palindrome string

Given a string, if it is a palindrome string, return the string, otherwise add the string to become a palindrome string

    def func(s: str):
        """
        给定一个字符串，若是回文字符串则返回该字符串，否则补充该字符串成为回文字符串
        例如：
        case1：
        输入：aba
        返回：aba

        case2：
        输入：abbc
        返回：abbcbba

        :param s:
        :return:
        """
        index = 0
        # 找出从后往前最长回文的对应的下标
        for i in range(len(s)):
            if s[i:][::-1] == s[i:]:
                index = i
                break
        # 如果下标为0，说明本身就是回文
        if index == 0:
            print(s)
        # 否则补充成回文字符串
        else:
            print(s+s[:index][::-1])