code: def process_host_line(line):
      
      if not line:
          return None, None
  
      host = None
      if _line_contains_host(line):
          url, host = re.split(SPLIT_PATTERN, line.strip())
      else:
          url = line.strip()
  
      return url, host
docs: Processes a line and determines whether it is a tab-delimited CSV of
      url and host.
  
      Strips all strings.
  
      @param line: the line to analyse.
      @param opts: the options dictionary to modify.
      @return: a tuple containing url, and host header if any change is
          required. Otherwise, line, null is returned.