EventHandler should normalize entities into iterable type

[huweiATgithub]

The problem

launch/launch/launch/event_handler.py

Lines 105 to 137 in 552bfac

	class EventHandler(BaseEventHandler):
	def __init__(
	self,
	*,
	matcher: Callable[[Event], bool],
	entities: Optional[SomeEntitiesType] = None,
	handle_once: bool = False
	) -> None:
	"""
	Create an EventHandler.
	:param: matcher is a callable that takes an event and returns True if
	the event should be handled by this event handler, False otherwise.
	:param: entities is an LaunchDescriptionEntity or list of them, and is
	returned by handle() unconditionally if matcher returns True.
	:param: handle_once is a flag that, if True, unregisters this EventHandler
	after being handled once.
	"""
	super().__init__(matcher=matcher, handle_once=handle_once)
	self.__entities = entities
	@property
	def entities(self):
	"""Getter for entities."""
	return self.__entities
	def describe(self) -> Tuple[Text, List[SomeEntitiesType]]:
	"""Return the description list with 0 as a string, and then LaunchDescriptionEntity's."""
	text, actions = super().describe()
	if self.entities:
	actions.extend(self.entities)
	return (text, actions)

In above code, entities: Optional[SomeEntitiesType] = None, entities is marked as SomeEntitiesType. It is not normalized in the __init__ function. In the describe function below, it is used as an iterable actions.extend(self.entities).

Besides, noting that in ExecuteLocal, entities is set to a single LaunchDescriptionEntity many times:

            EventHandler(
                matcher=lambda event: is_a_subclass(event, SignalProcess),
                entities=OpaqueFunction(function=self.__on_signal_process_event),
            )

Proposed fix

I plan to fix this by always making the __entities member an iterable (if not None):

        if isinstance(entities, LaunchDescriptionEntity):
            self.__entities = (entities,)
        else:
            self.__entities = entities