human
Solve the following python programming problem given the following code:
def _download(self, request, spider) : 
    def _on_success(response) : 
        assert isinstance (response, (Response, Request)) 
        if isinstance (response, Response) : 
            response.request = request 
            logging.info ((((spider.name + ':') + 'crawled url:') + response.url)) 
            self.signals.send_catch_log (signal = signals.response_received, response = response, request = request, spider = spider) 
return response 
dwld = self.downloader.fetch (request, dwld) 
    dwld.addCallbacks (_on_success) 
    return dwld 

    
    

    Fix the buggy line: dwld = self.downloader.fetch (request, dwld)
assistant
#Here is Python code to fix the buggy line: dwld = self.

dwld = self.downloader.fetch (request, spider)