docs: def __get_help_message(self, toks):
          """Write help message to file.
  
          Only called by the __driver_helper() method.
  
          Looks for the help message in the following order:
  
              1.  The helper method registered with this command via the @helper
                  decorator.
              2.  The doc string of the registered method.
              3.  A default help message basically saying 'no help found'.
  
          Arguments:
              toks: The list of command followed by its arguments.
  
          Returns:
              The help message.
  
          Raises:
               As this function is called via the readline complete callback, any
               errors and exceptions are silently ignored.
          """
          cmd = toks[0]
          if cmd in self._helper_map.keys():
              helper_name = self._helper_map[cmd]
              helper_method = getattr(self, helper_name)
              args = toks[1:] if len(toks) > 1 else []
              return helper_method(cmd, args)
  
          if cmd in self._cmd_map_all.keys():
              name = self._cmd_map_all[cmd]
              method = getattr(self, name)
              if method.__doc__:
                  return textwrap.dedent(method.__doc__)
  
          return textwrap.dedent('''\
                         No help message is found for:
                         {}
                         '''.format(textwrap.indent(
                             subprocess.list2cmdline(toks), '    ')))