Python FSM

This package contains a set of classes to handle a Finite State Machine (FSM).

Example usage

from python_fsm_handler.StateHandler import FsmHandler, StateLink, StateObject
from enum import Enum


moveCounter = 0
workCounter = 0

class FsmState(Enum):
    MOVE = 0
    WORK = 1
def test():

    def movePre():
        print("move pre")

    def moveExec():
        print("move exec")
        global moveCounter
        moveCounter += 1

    def movePost():
        print("move post")
        global moveCounter
        moveCounter = 0

    def workPre():
        print("work pre")
    
    def workExec():
        print("work exec")
        global workCounter
        workCounter += 1
    
    def workPost():
        print("work post")
        global workCounter
        workCounter = 0

    def loopCallback(state):
        print(f"loopCallback: {state}")
        print(f"moveCounter: {moveCounter}")
        print(f"workCounter: {workCounter}")
    def moveToWork():
        return moveCounter >= 5
    
    def workToMove():
        return workCounter >= 5

    states = [
        StateObject(FsmState.MOVE, [
            StateLink(FsmState.WORK, moveToWork)
        ], movePre, moveExec, movePost),
        StateObject(FsmState.WORK, [
            StateLink(FsmState.MOVE, workToMove)
        ], workPre, workExec, workPost),
    ]

    fsm = FsmHandler(states, FsmState.MOVE, logger=print, loopCallback=loopCallback)
    fsm.run()

if __name__ == "__main__":
    test()

This code will loop an FSM infinetely back and forth between two states. Running the code you may notice that the log in the loop callback will never print counter = 5 even if the 5 is reached. This is because the execution order in the state handler is as follow:

• exec current
• check condition for transition and if it's true change state
• exec loop callback So as you can see, the transition is happened, so the post condition reset the counter to 0 before printing in the loop callback