Example of State Machine with Switch Statement

state_machine_switch.py

"""
Simple state machine example and switch emulation.
"""


from enum import Enum
from typing import Iterable


class State(Enum):
    OPENED = 1
    CLOSED = 2


class Action(Enum):
    OPEN = 1
    CLOSE = 2
    
    
def update(state: State, action: Action) -> State:
    # Update function in the Elm style: 
    # https://elmprogramming.com/model-view-update-part-1.html 
    return {
        (State.CLOSED, Action.OPEN): State.OPENED,
        (State.OPENED, Action.CLOSE): State.CLOSED,
    }[(state, action)]


class Machine:
    """
    Creates a state machine as mutable object.
    """
    def __init__(self, *states: State):
        self._states = tuple(states)

    @property
    def state(self):
        """
        Gets a current states.
        """
        return self._states[-1]

    @property
    def states(self):
        """
        Gets a past and current state. 
        """
        return self._states

    def update(self, action: Action) -> 'Machine':
        """
        Update the machine state.
        """
        state = {
            (State.CLOSED, Action.OPEN): State.OPENED,
            (State.OPENED, Action.CLOSE): State.CLOSED,
        }[(self.state, action)]

        self._states += (state,)

    def updated(self, action: Action) ->  'Machine':
        """
        Get a new machine with updated state.
        """
        machine = (Machine(*self.states))
        machine.update(action)
        return machine


if __name__ == '__main__':
        
    print("-----------------------------------------------------------------------")
    print("1. Functional style `State -> Action -> State`.")
    print("-----------------------------------------------------------------------")
    
    door_state = State.OPENED
    door_state = update(door_state, Action.CLOSE)
    print(door_state)

    print("-----------------------------------------------------------------------")
    print("2. Object oriented style with mutable object.")
    print("-----------------------------------------------------------------------")
    door = Machine(State.OPENED)
    
    door.update(Action.CLOSE)
    door.update(Action.OPEN)
    door.update(Action.CLOSE)
    door.update(Action.OPEN)
    
    print(door.states) 

    print("-----------------------------------------------------------------------")
    print("3. Object oriented style with immutable object.")
    # This should be separated class, but for this example
    # we put the updated method to the existing object
    print("-----------------------------------------------------------------------")

    door_2 = door.updated(Action.CLOSE)
    print(door_2.states)