code: def download_handler(feed, placeholders):
      import shlex
      
      value = feed.retrieve_config('downloadhandler', 'greg')
      if value == 'greg':
          while os.path.isfile(placeholders.fullpath):
              placeholders.fullpath = placeholders.fullpath + '_'
              placeholders.filename = placeholders.filename + '_'
          urlretrieve(placeholders.link, placeholders.fullpath)
      else:
          value_list = shlex.split(value)
          instruction_list = [substitute_placeholders(part, placeholders) for
                              part in value_list]
          returncode = subprocess.call(instruction_list)
          if returncode:
              raise URLError
docs: Parse and execute the download handler