feature request: async callbacks

[harochau]

Looks like this library is supporting callbacks on transitions, but only regular ones.
I would like to use async def functions as callbacks, so I can use the same codebase (think async http requests, async database connections) in both API route handlers and state transitions.

[fgmacedo]

Hi @harochau , thanks for your suggestion. It would be nice to have async support.

Can you work on this? I'm still trying to figure it out how to have both sync and async on the same codebase.

[LoicRiegel]

I am also interested in using this library with an async codebase

[berland]

I see no blockers with using this with async code. I just wrote this proof of concept:

import asyncio
from statemachine import State, StateMachine


class TrafficLightMachine(StateMachine):
    "A traffic light machine"
    green = State(initial=True)
    yellow = State()
    red = State()

    # Transitions
    slowdown = green.to(yellow)
    shortcut = green.to(red)
    stop = yellow.to(red)
    go = red.to(green)

    cycle = slowdown | go | stop | go | shortcut

    def before_slowdown(self):
        print("Slowdown")

    def before_cycle(self, event: str, source: State, target: State, message: str = ""):
        message = ". " + message if message else ""
        print(f"Running {event} from {source.id} to {target.id}{message}")
        return

    def on_enter_red(self):
        asyncio.create_task(dont_move(3))

    def on_exit_red(self):
        asyncio.create_task(go_ahead())

async def amain():
    sma = TrafficLightMachine()
    sma.send("cycle")
    await asyncio.sleep(0)
    sma.send("cycle")
    await asyncio.sleep(0)
    sma.send("cycle")
    await asyncio.sleep(0)
    sma.send("cycle")
    await asyncio.sleep(0)
    sma.send("cycle")
    await asyncio.sleep(0)
    sma.send("cycle")
    await asyncio.sleep(0)
    sma.send("cycle")

async def dont_move(value):
    print(f"Don't move {value}")

async def go_ahead():
    print("Go ahead")

if __name__ == "__main__":
    asyncio.run(amain())

[fgmacedo]

@harochau @LoicRiegel @berland @xjules @sieroshtan can you help with tests/experimentation on the work done at PR #435?

Branch: macedo/async-sm.