Python Transations 库实现有限状态机（Finite-state machine, FSM）

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以视频播放器为例：

State List:

  • play
  • pause
  • stop

Action List:

  • toggle
  • forward
  • backward
  • stop

State Change Table View(list all transtions from one state to another with actions to trigger):

play pause stop
play forward/backward toggle stop
pause toggle forward/backward stop
stop toggle - -

Sample Code:

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from transitions import Machine

class Player(object):
    pass

model = Player()

states = ['play', 'pause', 'stop']

actions = ['toggle', 'forward', 'backward', 'stop']

transitions = [
    {'trigger': 'forward', 'source': 'play', 'dest': 'play' },
    {'trigger': 'backward', 'source': 'play', 'dest': 'play' },
    {'trigger': 'toggle', 'source': 'play', 'dest': 'pause'},
    {'trigger': 'stop', 'source': 'play', 'dest': 'stop'},
    {'trigger': 'toggle', 'source': 'pause', 'dest': 'play'},
    {'trigger': 'forward', 'source': 'pause', 'dest': 'pause'},
    {'trigger': 'backward', 'source': 'pause', 'dest': 'pause'},
    {'trigger': 'stop', 'source': 'pause', 'dest': 'stop'},
    {'trigger': 'toggle', 'source': 'stop', 'dest': 'play'}]

machine = Machine(model=model, states=states, transitions=transitions, initial='pause')

# Test
print(model.state)    # pause
model.toggle()
print(model.state)  #play
model.stop()
print(model.state)  #stop