human
Solve the following python programming problem given the following code:
def filter_fields(f) : 
    @ functools.wraps (f) 
    def inner_filter(* args, **kwargs) : 
        result = f (* args, ** kwargs) 
        fields = kwargs.get ('fields') 
        if (not fields) : 
            try : 
                pos = f.__code__.co_varnames.index ('fields') 
                fields = args [pos] 
except (IndexError, ValueError) : 
                return result 
do_filter = (lambda d : { k : v for (k, v) in d.items () if (k in fields) }) 
        if isinstance (result, list) : 
            return [do_filter (obj) for obj in result] 
else : 
            return do_filter (result) 
return f 

    
    

    Fix the buggy line: return f
assistant
#Here is Python code to fix the buggy line: return f
.

return def inner_filter(