fsm.py

LOCKED = 'locked'
UNLOCKED = 'unlocked'

PUSH = 'push'
COIN = 'coin'

class Fsm(object):

    def __init__(self, init_state, transitions, handler=None):
        self.state = init_state
        self.transitions = transitions
        self.handler = handler
                 
    def feed(self, input):
        next_state = self.transitions[self.state][input]
        handler_method = getattr(self.handler,
                                 '{}_{}'.format(self.state, next_state), 
                                 None)
        self.state = next_state
        if handler_method:
            handler_method(input)
        

class TransistionHandler(object):
    
    def locked_unlocked(self, input):
        print '{} : transition from locked to unlocked'.format(input)

    def unlocked_locked(self, input):
        print '{} : transition from unlocked to locked'.format(input)


fsm = Fsm(init_state=LOCKED, 
          transitions={
              LOCKED: {PUSH: LOCKED,
                       COIN: UNLOCKED},
              UNLOCKED: {PUSH: LOCKED, 
                         COIN: UNLOCKED}
          },
          handler=TransistionHandler())

fsm.feed(COIN)
fsm.feed(PUSH)

from collections import namedtuple
Edge = namedtuple('Edge', 'start end label')

def edges(transitions):
    return (Edge(start, end, label) 
             for (start, evt_end) in transitions.iteritems()
             for (label, end) in evt_end.iteritems())

def edge_to_dot(edge):
    return '{start} -> {end} [ label = "{label}" ];'.format(**edge._asdict())

def dot_file(filename, transitions):
    content = 'digraph finite_state_machine {\n%s\n}' % '\n'.join(edge_to_dot(e) for e in edges(transitions))
    with open(filename, 'w') as f:
        f.write(content)


dot_file('fsm.dot', fsm.transitions)