pystate 0.1.1
Python package for co-routine base state machines.
License: MIT
Keywords: state machine,coroutine,co-routine

FiniteStateMachine - A finite state machine class using coroutines

    FiniteStateMachine is a class representing a finite state machine. Each state is represented by an instance of the
    State class. Each state also has a state handler function defined for it. The handler function is a co-routine that
    excepts an event and performs an action based on it.

    To define the state machine:

    1) define the states (e.g. STATE_A = State('STATE_A'))
    2) define the state handler functions. See below for the structure of a state handling function.
    3) create an instance of the state machine (e.g. fsm = Fsm())
    4) add states to the state machine, including exactly one state marked as the initial state. Each state also takes
        a sequence of states that it can be transitioned from (from_states).
    5) call the start function on the FSM (e.g. fsm.start())

    For each event you will need to call the dispatch_event function (e.g. fsm.dispatch_event()) to route the event
    to the co-routine. An event can be anything you want (e.g. a tuple with event_id and arguments). The main loops
    generally looks like:

    try:
        while True:
            event = get_next_event()
            fsm.dispatch_event(event)
    except ExpectedExit as e:
        pass

    The basic structure of a state handler is:

    def state_handler_<state name>(fsm):
        # Enter the main loop for the co-routine
        while True:
            event = yield

            if event == 'EVENT_1':
                # Transition to another state
                fsm.transition_to(STATE_X)
            elif event == 'EVENT_2':
                # Do some processing but stay in this state
                print('Got EVENT_2')
            elif event == 'TERMINATING_EVENT':
                raise FsmExit
            else:
                print('Unrecognized event (%s)' % event)

    A simple example of this is shown in the turnstile_test.py test case.

    For convenience this can be wrapped with a @state_handler decorator. The decorator takes care of the co-routine
    boiler plate and hands the handler function an fsm and event. This would look like:

    @pystate.state_handler
    def state_locked_handler(event, fsm):
        if event == 'EVENT_1':
            # Transition to another state
            fsm.transition_to(STATE_X)
        elif event == 'EVENT_2':
            # Do some processing but stay in this state
            print('Got EVENT_2')
        elif event == 'TERMINATING_EVENT':
            raise FsmExit
        else:
            print('Unrecognized event (%s)' % event)

    There are two ways to handle a state that needs to keep persistant data. You can create a callable clas (i.e. define
    the __call__ dunder method to call as the state handler.) This allows you to use the state_handler decorator around
    the __call__ method. Alternatively, you can set the state data above the while loop if you define the co-routine by
    hand, however, this precludes using the decorator. See the callable_test.py test case for an example.

Author: Len Wanger
Last Updated: 7/7/2016
Copyright (c) 2016 Len Wanger

Permission is hereby granted, free of charge, to any person obtaining a copy
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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Note: Substantial code was adapted from Christian Maugg's pystatemachine code
Copyright (c) 2015 Christian Maugg
(https://raw.githubusercontent.com/cmaugg/pystatemachine/master/pystatemachine.py)