human
Solve the following python programming problem given the following code:
def _auth_return_future(f) : 
    "Similar to tornado.concurrent.return_future, but uses the auth
    module's legacy callback interface.

    Note that when using this decorator the ``callback`` parameter
    inside the function will actually be a future.
    " 
    replacer = ArgReplacer (wrapper, 'callback') 
    @ functools.wraps (f) 
    def wrapper(* args, **kwargs) : 
        future = Future () 
        (callback, args, kwargs) = replacer.replace (future, args, kwargs) 
        if (callback is not None) : 
            future.add_done_callback (functools.partial (_auth_future_to_callback, callback)) 
f (* args, ** kwargs) 
        return future 
return wrapper 

    
    

    Fix the buggy line: replacer = ArgReplacer (wrapper, 'callback')
assistant
#Here is Python code to fix the buggy line: replacer = ArgReplacer (wrapper, 'callback')
.

replacer = ArgReplacer (f, 'callback')