target state in an transition before or after callback

[spitzlbergerj]

Hi,

I'm new to using the transitions library, but I'm getting along quite well.

I have the following definition of states and transitions

	states = [
		{'name': 'INIT',	'on_enter': ['init_leds_on_enter'],		'on_exit': ['init_leds_on_exit']},
		{'name': 'OFF',		'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},
		{'name': 'AUTO',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},
		{'name': 'HAND',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},

		{'name': 'WAIT2AUTO',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},
		{'name': 'WAIT2HAND',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},
		{'name': 'WAIT2OFF',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},

		{'name': 'BLOCKED',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},

		{'name': 'ERROR',	'on_enter': ['manage_leds_on_enter'], 		'on_exit': ['manage_leds_on_exit']},
	]


	transitions = [
		{'trigger': 'initialize',	'source': 'INIT', 	'dest': 'OFF'},

		{'trigger': 'to_auto',		'source': 'OFF',	'dest': 'WAIT2AUTO',	'conditions': 'can_transition', 'before': 'before_move', 'after': 'move_motor'},
		{'trigger': 'to_hand',		'source': 'OFF',	'dest': 'WAIT2HAND',	'conditions': 'can_transition', 'before': 'before_move', 'after': 'move_motor'},
		{'trigger': 'to_off',		'source': 'HAND',	'dest': 'WAIT2OFF',	'conditions': 'can_transition', 'before': 'before_move', 'after': 'move_motor'},
		{'trigger': 'to_off',		'source': 'AUTO',	'dest': 'WAIT2OFF',	'conditions': 'can_transition', 'before': 'before_move', 'after': 'move_motor'},

		{'trigger': 'wait',		'source': 'WAIT2AUTO',	'dest': 'AUTO',		'conditions': 'can_transition', 'after': 'waiting'},
		{'trigger': 'wait',		'source': 'WAIT2HAND',	'dest': 'HAND',		'conditions': 'can_transition', 'after': 'waiting'},
		{'trigger': 'wait',		'source': 'WAIT2OFF',	'dest': 'OFF',		'conditions': 'can_transition', 'after': 'waiting'},

		{'trigger': 'block',		'source': '*',		'dest': 'BLOCKED', 	'before': 'store_state'},
		{'trigger': 'unblock',		'source': 'BLOCKED',	'dest': None, 		'before': 'restore_state'},
		{'trigger': 'error',		'source': '*',		'dest': 'ERROR'},
	]


	def __init__(self):
		self.fountainUnit = Machine(model=self, states=DeviceController.states, transitions=DeviceController.transitions, initial='INIT', queued=True)

I would now like to know in the callbacks before_move and move_motor which target status should be changed to. For this I would need either the trigger or the target status.

Unfortunately, I can't get any further at this point? How do I query trigger or target status?

	def before_move(self):
		destination = None  # ????

		logging.info(f"before_move: Source: {self.state} Destination: {destination}")

		print("Aktivitäts LED blinken lassen")

	def move_motor(self):
		destination = None # ????

		logging.info(f"move_motor: Source: {self.state} Destination: {destination}")

		print("Motor drehen")

		if destination == "OFF":
			print("Zielstatus = OFF, daher Fine-Tuning Schlüsselstellung")

		print("Statuswechsel Warten aufrufen")
		self.wait()

Thank you very much!

Grüße
Sepp

[aleneum]

Hello @spitzlbergerj,

maybe send_event=True(see Readme section Passing Data) is what you are looking for:

[...] Transitions supports an alternate method for sending data. If you set send_event=True at Machine initialization, all arguments to the triggers will be wrapped in an EventData instance and passed on to every callback. (The EventData object also maintains internal references to the source state, model, transition, machine, and trigger associated with the event, in case you need to access these for anything.)

from transitions import Machine
from transitions.core import EventData


class Model:

    def before_cb(self, event_data: EventData) -> None:
        print("===== Before Transition ====")
        print(f"Trigger: {event_data.event.name}")
        print(f"Source: {event_data.transition.source}")
        print(f"Dest: {event_data.transition.dest}")
        print(f"Args: {event_data.args}")
        print(f"Kwargs: {event_data.kwargs}")
        print("-" * 28)


states = ["A", "B", "C"]
transitions = [{"trigger": "go", "source": "A", "dest": "B", "before": "before_cb"},
               {"trigger": "go", "source": "B", "dest": "C", "before": "before_cb"}]

model = Model()
machine = Machine(model, states=states, transitions=transitions, send_event=True, initial="A")
model.go(1, fast=False)
model.go(super_fast=True, power=42)

[spitzlbergerj]

Thank you very much, @aleneum ,

I discovered this option yesterday evening and was already on this track. Your code snippet helps me a lot because I had not found what structure event has and how to access individual parts.

So thank you very much

Best regards
Sepp