使用python

Question

s='sqrileksarrawixamwabj'
pos = 0
maxLen = 0
startPos = 0
endPos = 0


def last_pos(pos):
    if pos < (len(s) - 1):
        if s[pos + 1] >= s[pos]:
            pos += 1
            if pos == len(s)-1:
                return len(s)
            else:
                return last_pos(pos)
        return pos


for i in range(len(s)):
    if last_pos(i) != None:
        diff = last_pos(i) - i + 1
    if diff > maxLen:
        maxLen = diff
        startPos = i
        endPos = startPos + diff - 1

print "Longest substring in alphabetical order is:"+ s[startPos:endPos+1]

现在输出变为＆＃39; abj＆＃39;但是还有其他子字符串，例如＆＃39; eks＆＃39;并且＆＃39; amw＆＃39;。我想要的是输出应该是＆＃39; eks＆＃39;它首先作为s中的子串而不是＆＃39; abj＆＃39;这是最后出现的子字符串。应该在上面的代码中进行哪些修改，以便获得所需的输出？