寻找最长不含有重复字符的子串

s = "abcdbabc"

def max_str(s):
    max_str = ''
    str_li = ''
    for i in s:
        if i not in str_li:
            str_li+=i
        else:
            str_li = str_li[str_li.index(i)+1:]
            str_li+=i
        max_str = str_li if len(str_li) > len(max_str) else max_str

        print(max_str)
        print(len(max_str))

max_str(s)