state_machines_retry.py

class Payments(models.Model):
    STATES = {
        'started': 'Started',
        'captured': 'Captured',
        'completed': 'Completed',
        'incomplete': 'Incomplete',  # new incomplete state for us
    }

    def __init__(self, *args, **kwargs):
        super(Payments, self).__init__(*args, **kwargs)

        # Initialize the state machine
        self.machine = Machine(
            model=self,
            states=self.STATES.keys(),
            initial='started',
            after_state_change='save',
        )

        self.machine.add_transition(
            trigger='capture',
            source='started',
            destination='captured',
            # we check only enter captured state if the payment is captured
            # otherwise we go to incomplete, as you can see in the next
            # transition
            conditions=['has_captured_payment',],
        )

        self.machine.add_transition(
            trigger='capture',
            source='started',
            destination='incomplete',
        )

        self.machine.add_transition(
            trigger='retry',
            source='incomplete',
            destination='completed',
            # similarly, we only go from incomplete to complete if the payment
            # is captured, otherwise we stay as incomplete
            conditions=['has_captured_payment',],
        )

        self.machine.add_transition(
            trigger='retry',
            source='incomplete',
            destination='incomplete',
        )

        self.machine.add_transition(
            trigger='complete',
            source='captured',
            destination='completed',
        )

        # we notify the user whenever we enter “complete” state, this
        # this calls self.notify_user()
        self.machine.on_enter_complete('notify_user')

    def has_captured_payment(self):
        try:
            self.contact_payment_gateway()
        except PaymentGatewayException:
            return False
        return True