required_slots.py

@staticmethod
def required_slots(tracker: Tracker) -> List[Text]:

	# this should run as soon as the form starts
	if not tracker.get_slot('time'):
		return ["time", "call_hhmmss"]
	
	# this should happen every other time
	else:
		t = None # initialize t as None
		t_str = tracker.get_slot('time') # get the duckling time string from slot

		try:
			# try to convert to date object
			t = dt.strptime(t_str, "%Y-%m-%dT%H:%M:%S.%f%z")
		except Exception as e:
			SlotSet("time", None)
			return ["time", "call_hhmmss"]

		# if we got here, we got a real date object

		if t.hour == 0 and t.minute == 0 and t.second == 0:
			# here, we know the user said just a date rather than a datetime

			# set call_date
			SlotSet("call_date", t.strftime("%Y-%m-%d"))
			
			# leave call_hhmmss null
			# leave call_time null

			# return this so the user is asked for the specific time
			return ["time", "call_hhmmss"]


		else:
			# here, we know it was a valid date+time, so we're good

			print("Found entirely valid date")

			# first, check if call_date was already set
			if tracker.get_slot('call_date'):

				print("Call date was already set")

				# if we already have a date, just append the new time,
				# and save that to call_time

				call_date = tracker.get_slot("call_date")

				# call_date is already set

				# set call_hhmmss via time
				call_hhmmss = t.strftime("%H:%M:%S.%f%z")
				SlotSet("call_hhmmss", call_hhmmss)

				# set call_time as call_date + call_hhmmss
				time_str = call_date + 'T' + call_hhmmss
				SlotSet("call_time", time_str)

				# returning this is fine because at this point, all four
				# values will already be filled
				return ["time", "call_time", "call_date", "call_hhmmss"]

			else:

				print("Call date was not yet set")

				# this is a good scenario, user provided all info immediately

				# set call_date via time
				call_date = t.strftime("%Y-%m-%d")
				SlotSet("call_date", call_date)

				# set call_hhmmss via time
				call_hhmmss = t.strftime("%H:%M:%S.%f%z")
				SlotSet("call_hhmmss", call_hhmmss)

				# set call_time as call_date + call_hhmmss
				time_str = call_date + 'T' + call_hhmmss
				SlotSet("call_time", time_str)

				# returning this is fine because at this point, all four
				# values will already be filled
				return ["time", "call_time", "call_date", "call_hhmmss"]