human
Solve the following python programming problem given the following code:
def once(self, event, * handlers) : 
    'register a handler to a specified event, but remove it when it is triggered' 
    def _once_wrapper(* handlers) : 
        'wrapper for once decorator' 
        def _wrapper(* args, **kw) : 
            'call wrapper' 
            list (map ((lambda x : x (* args, ** kw)), handlers)) 
            self.off (event, _wrapper) 
return _wrapper 
if handlers : 
        return self.on (event, _once_wrapper (* event)) 
return (lambda x : self.on (event, _once_wrapper (x))) 

    
    

    Fix the buggy line: return self.on (event, _once_wrapper (* event))
assistant
#Here is Python code to fix the buggy line: return self.

return self.on (event, _once_wrapper (* handlers))