human
Solve the following python programming problem given the following code:
def _create_async_completer(self, buffer) : 
    '
        Create function for asynchronous autocompletion.
        (Autocomplete in other thread.)
        ' 
    complete_thread_running = [False] 
    def async_completer(select_first = False, select_last = False, insert_common_part = False, complete_event = None) : 
        document = buffer.document 
        complete_event = (complete_event or CompleteEvent (text_inserted = True)) 
        if complete_thread_running [0] : 
            return 
if (buffer.complete_state or (not buffer.completer)) : 
            return 
complete_thread_running [0] = True 
        def run() : 
            completions = list (buffer.completer.get_completions (document, complete_event)) 
            complete_thread_running [0] = False 
            def callback() : 
                "
                    Set the new complete_state in a safe way. Don't replace an
                    existing complete_state if we had one. (The user could have
                    pressed 'Tab' in the meantime. Also don't set it if the text
                    was changed in the meantime.
                    " 
                if ((buffer.text == document.text) and (buffer.cursor_position == document.cursor_position) and (not buffer.complete_state)) : 
                    set_completions = True 
                    select_first_anyway = False 
                    if insert_common_part : 
                        common_part = get_common_complete_suffix (document, completions) 
                        if common_part : 
                            buffer.insert_text (common_part) 
                            async_completer () 
                            set_completions = False 
else : 
                            if (len (completions) == 1) : 
                                select_first_anyway = True 
if set_completions : 
                        buffer.set_completions (completions = completions, go_to_first = (select_first or select_first_anyway), go_to_last = select_last) 
self.invalidate () 
else :...

    
    

    Fix the buggy line: return buffer
assistant
#Here is Python program to fix the buggy line: return buffer
.

return async_completer