1 class SignalState: 2 Red = 1 3 Amber = 2 4 Green = 3 5 AmberAgain = 4 6 Off = None 7 8 class Signal: 9 def __init__(self): 10 self.disable() 11 12 def enable(self): 13 self.state = SignalState.Red 14 15 def disable(self): 16 self.state = SignalState.Off 17 18 def next(self): 19 if self.state == SignalState.Red: 20 self.state = SignalState.Amber 21 elif self.state == SignalState.Amber: 22 self.state = SignalState.Green 23 elif self.state == SignalState.Green: 24 self.state = SignalState.AmberAgain 25 elif self.state == SignalState.AmberAgain: 26 self.state = SignalState.Red 27 else: 28 self.state = SignalState.Off 29 30 s = Signal() 31 print s.state # None 32 s.next() 33 print s.state # None 34 s.enable() 35 print s.state # 1 36 s.next() 37 print s.state # 2 38 s.next() 39 print s.state # 3 40 s.next() 41 print s.state # 4 42 s.next() 43 print s.state # 1
