one gramar doubt of the "before_state_change"

[LifeIsBinary]

thanks for this job of FSM library.

Maybe I do not understand some term and regular of FSM.

I have some doubt as fllow： `
//1. define a fsm self.machine = Machine(model=self, states=NaoController.states, before_state_change='set_IS_STAND', send_event=True, initial='init')

    // 2.  "init" to "prepared"
    self.machine.add_transition(trigger='control_start',
                                source='init', dest='prepared',before='robot_init',
                                conditions='is_stand')

`

above the code , I found one thing: state transition condtion is justify before the method: set_IS_STAND, if i want to change the parameter: is_stand before condition justify，i need to use ”before“ or ”prepare_event“ ？

thank your！

[aleneum]

Hello @LifeIsBinary,

the Callback execution order in the documentation states the following:

Callback | Current State | Comments -- | -- | -- 'machine.prepare_event' | source | executed once before individual transitions are processed 'transition.prepare' | source | executed as soon as the transition starts 'transition.conditions' | source | conditions may fail and halt the transition 'transition.unless' | source | conditions may fail and halt the transition 'machine.before_state_change' | source | default callbacks declared on model 'transition.before' | source |  

Thus, callbacks are executed in the order prepare_event, prepare, conditions/unless, before_state_change, before and so on. As failed conditions halt the transition, before and all following callbacks are only called when the state transition will actually happen. Conditions must had been processed and evaluated to True already. If you want callbacks to execute before conditions or unless you need to use either machine.prepare_event or transition.prepare.

Closing this since it's a question about how to use transitions.

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