How to get the callback result?

[vba34520]

from transitions import Machine


class TempMachine(Machine):
    def __init__(self):
        self.temp = 0
        states = ['centigrade', 'fahrenheit', 'kelvin']
        Machine.__init__(self, states=states, send_event=True, initial=states[0],
                         ignore_invalid_triggers=True, auto_transitions=False)
        self.add_transition(trigger='to_centigrade', source='*', dest='centigrade', before='set_temp',
                            after='calc_temp')

    def set_temp(self, event):
        self.temp = event.kwargs.get('temp', 0)

    def calc_temp(self, event):
        temp_map = {}
        if event.transition.dest == 'centigrade':
            temp_map = {
                'centigrade': '{} ℃'.format(self.temp),
                'fahrenheit': '{} ℉'.format(self.temp * 1.8 + 32),
                'kelvin': '{} K'.format(self.temp + 273.15)
            }
        print(temp_map)
        return temp_map


machine = TempMachine()
machine.to_centigrade(temp=25)

It's it possible to get the temp_map? Thanks!

[aleneum]

Hello @vba34520,

callback return values are ignored (unless they are conditions, in this case they must return a 'truesy' or 'falsy' value).
You cannot directly return values from callbacks.
You can either assign variables to your stateful object (the model; in your case also the machine; e.g. self.temp_map) or pass a referenced object as a parameter:

from transitions import Machine


class TempMachine(Machine):
    def __init__(self):
        self.temp = 0
        states = ['centigrade', 'fahrenheit', 'kelvin']
        Machine.__init__(self, states=states, send_event=True, initial=states[0],
                         ignore_invalid_triggers=True, auto_transitions=False)
        self.add_transition(trigger='to_centigrade', source='*', dest='centigrade', before='set_temp',
                            after='calc_temp')

    def set_temp(self, event):
        self.temp = event.kwargs.get('temp', 0)

    def calc_temp(self, event):
        referenced_map = event.kwargs.get("temp_map")
        if event.transition.dest == 'centigrade':
            referenced_map.update({
                'centigrade': '{} ℃'.format(self.temp),
                'fahrenheit': '{} ℉'.format(self.temp * 1.8 + 32),
                'kelvin': '{} K'.format(self.temp + 273.15)
            })


temp_map = {}
machine = TempMachine()
machine.to_centigrade(temp_map=temp_map, temp=25)
assert temp_map["fahrenheit"] == "77.0 ℉"