pyfsm-tool

pyfsm-tool is a module to create and manipulate finite states machines (fsm).

Getting started

Import modules

FiniteStateMachine module:

from pyfsm_tool import FiniteStateMachine, StateBehaviour

Exceptions module:

from pyfsm_tool import FSMException

Create new FSM

The new fsm is empty (No state and no transition).

fsm: FiniteStateMachine = FiniteStateMachine()

Initialize the fsm data store

Initialize fsm data store wit 'message' and 'count' available for all states.

fsm.fsm_data_store = {"message": "", "count": 0}

Create new behaviours

Create new behaviours for fsm states.

• First behaviour: add 'Hello' in fsm data store (key = 'message') and next transition is 't1'

class Behaviour1(StateBehaviour):
    def action(self) -> None:
        self.state_data_store["message"] += "Hello"

    def next_transition_id(self) -> str:
        return "t1"

• Second behaviour: add ' ' in fsm data store (key = 'message') and next transition is 't2'

class Behaviour2(StateBehaviour):
    def action(self) -> None:
        self.state_data_store["message"] += " "

    def next_transition_id(self) -> str:
        return "t2"

• Third behaviour: add 'world' in fsm data store (key = 'message') and next transition is 't3'

class Behaviour3(StateBehaviour):
    def action(self) -> None:
        self.state_data_store["message"] += "world"

    def next_transition_id(self) -> str:
        return "t3"

• Fourth behaviour: add '!' in fsm data store (key = 'message') and next transition is 't4' (itself) if the key 'count' in fsm data store is less than 2 (there is incrementation of fsm data store for key 'count'), else next transition is 't5'

class Behaviour4(StateBehaviour):
    def action(self) -> None:
        self.state_data_store["message"] += "!"

    def next_transition_id(self) -> str:
        if self.state_data_store.get("count") < 2:
            self.state_data_store["count"] += 1
            return "t4"
        return "t5"

• Fifth behaviour: display fsm data store (key = 'message') and finish fsm.

class Behaviour5(StateBehaviour):
    def action(self) -> None:
        print(self.state_data_store.get("message"))

Register all states

• Register first state with first behaviour

fsm.register_first_state(Behaviour1(), "b1")

• Register next states with next behaviours

fsm.register_state(Behaviour2(), "b2")
fsm.register_state(Behaviour3(), "b3")
fsm.register_state(Behaviour4(), "b4")

• Register last state with last behaviour

fsm.register_last_state(Behaviour5(), "b5")

If state behaviour not inherits StateBehaviour class or if state already exists(same id) or if an argument is None, then FSMException is raise.

try:
    fsm.register_state(Behaviour2(), "b2")
except FSMException as error:
    pass  # or do something...

Register all transitions

fsm.register_transition("b1", "b2", "t1")
fsm.register_transition("b2", "b3", "t2")
fsm.register_transition("b3", "b4", "t3")
fsm.register_transition("b4", "b4", "t4")
fsm.register_transition("b4", "b5", "t5")

If transition already exists(same id) or if an argument is None, then FSMException is raise.

try:
    fsm.register_transition("b1", "b2", "t1")
except FSMException as error:
    pass  # or do something...

Run FSM

fsm.run()

Author

If you have any questions or suggestions, please don't hesitate to contact me : belaich.david@outlook.fr.