human
Solve the following python programming problem given the following code:
def fetch(self, request, callback = None, **kwargs) : 
    "Executes a request, asynchronously returning an `HTTPResponse`.

        The request may be either a string URL or an `HTTPRequest` object.
        If it is a string, we construct an `HTTPRequest` using any additional
        kwargs: ``HTTPRequest(request, **kwargs)``

        This method returns a `.Future` whose result is an
        `HTTPResponse`.  The ``Future`` wil raise an `HTTPError` if
        the request returned a non-200 response code.

        If a ``callback`` is given, it will be invoked with the `HTTPResponse`.
        In the callback interface, `HTTPError` is not automatically raised.
        Instead, you must check the response's ``error`` attribute or
        call its `~HTTPResponse.rethrow` method.
        " 
    if (not isinstance (kwargs, HTTPRequest)) : 
        request = HTTPRequest (url = request, ** kwargs) 
request.headers = httputil.HTTPHeaders (request.headers) 
    request = _RequestProxy (request, self.defaults) 
    future = Future () 
    if (callback is not None) : 
        callback = stack_context.wrap (callback) 
        def handle_future(future) : 
            exc = future.exception () 
            if (isinstance (exc, HTTPError) and (exc.response is not None)) : 
                response = exc.response 
else : 
                if (exc is not None) : 
                    response = HTTPResponse (request, 599, error = exc, request_time = (time.time () - request.start_time)) 
else : 
                    response = future.result () 
self.io_loop.add_callback (callback, response) 
future.add_done_callback (handle_future) 
def handle_response(response) : 
        if response.error : 
            future.set_exception (response.error) 
else : 
            future.set_result (response) 
self.fetch_impl (request, handle_response) 
    return future 

    
    

    Fix the buggy line: if (not isinstance (kwargs, HTTPRequest)) :
assistant
#Here is Python code to fix the buggy line: if (not isinstance (kwargs, HTTPRequest)) :
.

if (not isinstance (request, HTTPRequest)) :