human
Solve the following python programming problem given the following code:
def mark_end_segment(str, is_segment) : 
    def mark_start(s) : 
        if (s [0 : 1] == 'x') : 
            return (s [: (- 1)] + 's') 
else : 
            return s 
return ''.join (map (mark_start, split_words (str, mark_start))) 

    
    

    Fix the buggy line: return ''.join (map (mark_start, split_words (str, mark_start)))
assistant
#Here is Python program to fix the buggy line: return ''.

return ''.join (map (mark_start, split_words (str, is_segment)))