Traffic light machine

This example demonstrates how to create a traffic light machine using the statemachine library.

The state machine will run in a dedicated thread and will cycle through the states.

import time
from threading import Event as ThreadingEvent
from threading import Thread

from statemachine import State
from statemachine import StateMachine


class TrafficLightMachine(StateMachine):
    "A traffic light machine"

    green = State(initial=True)
    yellow = State()
    red = State()

    cycle = green.to(yellow) | yellow.to(red) | red.to(green)

    def before_cycle(self, event: str, source: State, target: State):
        print(f"Running {event} from {source.id} to {target.id}")

Run in a dedicated thread

class Supervisor:
    def __init__(self, sm: StateMachine, sm_event: str):
        self.sm = sm
        self.sm_event = sm_event
        self.stop_event = ThreadingEvent()

    def run(self):
        while not self.stop_event.is_set():
            self.sm.send(self.sm_event)
            self.stop_event.wait(0.1)

    def stop(self):
        self.stop_event.set()


def main():
    supervisor = Supervisor(TrafficLightMachine(), "cycle")
    t = Thread(target=supervisor.run)
    t.start()

    time.sleep(0.5)
    supervisor.stop()
    t.join()


if __name__ == "__main__":
    main()

Running cycle from green to yellow
Running cycle from yellow to red
Running cycle from red to green
Running cycle from green to yellow
Running cycle from yellow to red