state_machines.py

class Payments(models.Model):
    STATES = {
        'started': 'Started',
        'captured': 'Captured',
        'completed': 'Completed',
    }

    state = models.CharField(default='started', choices=STATES.items(), max_length=16)

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

        # Initialize the state machine
        self.machine = Machine(
            model=self,  # the object on which the library attaches trigger functions
            states=self.STATES.keys(),  # states in the state machine
            initial='started',  # initial state of the machine
            after_state_change='save',  # method to call after state change, this will call self.save()
        )

        # Lets add transitions to our state machine, we can now call self.capture() to perform
        # the transition and capture a payment
        self.machine.add_transition(
            trigger='capture',
            source='started',
            destination='captured',
            before='contact_payment_gateway',
        )
        # We can now call self.complete() to perform the transition and complete a payment
        self.machine.add_transition(
            trigger='complete',
            source='captured',
            destination='completed',
            after='notify_user',
        )