Python 字符串索引超出范围DNA回文组

我不明白为什么字符串超出范围，以及如何修复它。 如果我知道问题所在，我可以尝试解决它，但我不理解问题所在 代码如下：

def get_odd_palindrome_at(s1, number):
    '''(str, int) -> str
    precondition: int is valid index in s1
        return str of longest odd palindrome, of which the middle is number. 
    '''

    if s1[number-1] != s1[number+1]:
        return s1[int]
    num =  1 
    while num < len(s1):
        if s1[number-num] == s1[number+num]: 
            num= num +1 
    return s1[number-num: number+num+1] 

get_odd_palindrome_at("AGTGAT", 2)

def get_奇数_回文_at（s1，数字）：
''（str，int）->str
前提条件：int是s1中的有效索引
返回最长奇数回文的str，中间是数字。
'''
如果s1[1号]！=s1[编号+1]：
返回s1[int]
num=1
当num

我发现两个问题

在语句

returns1[int]

int不是s1的有效索引

在循环中，num与len（s1）-1一样高。在声明中的这一点上

如果s1[number num]==s1[number+num]：

---

number+num

超出范围。

您必须调整2个命令以正确检查索引是否在范围内，并修复1个错误：

而不是

    if s1[number-1] != s1[number+1]:         # number + 1 may be too large
        return s1[int]                       # it is error

使用

而不是

    while num < len(s1):                     # it isn't sufficient condition
        if s1[number-num] == s1[number+num]: # it is OK; only for context

whilenum

使用更复杂但正确的条件

    while number - num >= 0  and  number + num <= len(s1) - 1:
        if s1[number-num] == s1[number+num]:

而number-num>=0和number+num len（s1）-1或s1[number-1]！=s1[编号+1]：
返回s1[编号]
num=1
当number-num>=0且此处的number+num>s1[number-num:number+num+1]时，检查此时的num是什么。什么数字加上num+1是因为我打赌它比len（s1）大。
    while number - num >= 0  and  number + num <= len(s1) - 1:
        if s1[number-num] == s1[number+num]:

def get_odd_palindrome_at(s1, number):
    '''(str, int) -> str
    precondition: int is valid index in s1
        return str of longest odd palindrome, of which the middle is number. 
    '''

    if number + 1 > len(s1) - 1  or  s1[number-1] != s1[number+1]:
        return s1[number]

    num =  1

    while number - num >= 0  and  number + num <= len(s1) - 1:
        if s1[number-num] == s1[number+num]: 
            num= num +1
            print(number, num)
    return s1[number-num: number+num+1] 

get_odd_palindrome_at("AGTGAT", 2)