在状态模式（State Pattern）中，类的行为是基于它的状态改变的。这种类型的设计模式属于行为型模式。

在状态模式中，我们创建表示各种状态的对象和一个行为随着状态对象改变而改变的 context 对象。

 

class State(object):    """Base state. This is to share functionality"""    def scan(self):        """Scan the dial to the next station"""        self.pos += 1        if self.pos == len(self.stations):            self.pos = 0        print("Scanning... Station is", self.stations[self.pos], self.name)class AmState(State):    def __init__(self, radio):        self.radio = radio        self.stations = ["1250", "1380", "1510"]        self.pos = 0        self.name = "AM"    def toggle_amfm(self):        print("Switching to FM")        self.radio.state = self.radio.fmstateclass FmState(State):    def __init__(self, radio):        self.radio = radio        self.stations = ["81.3", "89.1", "103.9"]        self.pos = 0        self.name = "FM"    def toggle_amfm(self):        print("Switching to AM")        self.radio.state = self.radio.amstateclass Radio(object):    """A radio.     It has a scan button, and an AM/FM toggle switch."""    def __init__(self):        """We have an AM state and an FM state"""        self.amstate = AmState(self)        self.fmstate = FmState(self)        self.state = self.amstate    def toggle_amfm(self):        self.state.toggle_amfm()    def scan(self):        self.state.scan()# Test our radio outif __name__ == '__main__':    radio = Radio()    actions = [radio.scan] * 2 + [radio.toggle_amfm] + [radio.scan] * 2    actions = actions * 2    for action in actions:        action()