code: def _fetch_url(url, is_threaded, timeout=None):
          
          headers = {'User-Agent': 'Mozilla/5.0'}
          req = urllib.request.Request(url, None, headers)
          html = urllib.request.urlopen(req, data=None, timeout=timeout).read()
  
          if is_threaded:
              SimpleCrawler._results[url] = html
  
          return html
docs: Crawls the html content of the parameter url and saves the html in _results
          :param url:
          :param is_threaded: If True, results will be stored for later processing by the fetch_urls method. Else not.
          :param timeout: in seconds, if None, the urllib default is used
          :return: html of the url