小编Jor*_*ron的帖子

我的代码给我一个错误，说第 9 行的索引超出范围。这是我的代码：

s = 'aba'
letter = ''
substring = ''

i = 0

while(i <= len(s)):
    prev_letter = s[0]
    letter = s[i]

    if letter <= prev_letter:
        substring += letter
        prev_letter = letter

    i += 1