Python:Palidrome(字符串索引超出范围)

我试着编写一个名为is_palidrome_v3(s)的方法来比较单词的第一个和最后一个字母,然后是第二个和最后一个字母,直到该对不相同,最后检查索引是否> = len(s)// 2

def is_palidrome_v3(s):
    ''' (str) -> bool

    Return True if and only if s is a palidrome.

    >>> is_palidrome_v3('noon')
    True
    >>> is_palidrome_v3('racecar')
    True
    >>> is_palidrome_v3('dented')
    False
    '''

    i = 0
    while i <= len(s) // 2 and s[i] == s[len(s) - i]:
        i = i + 1

    return i >= len(s)//2

但是当我运行它时:

is_palidrome_v3('noon')

有一个错误:

Traceback (most recent call last): 
File "", line 1, in  is_palidrome_v3('noon') 
File "C:\Users\James\Google-h0925473\Learning Programming\Python\Python Fundamental (Coursera)\is_palidrome_v1.py", line 67, in is_palidrome_v3 while i <= len(s) // 2 and s[i] == s[len(s) - i]: 
IndexError: string index out of range 

有人可以告诉我里面有什么不对吗？

谢谢!!!