设计模式-状态模式-state-python

def

当一个对象内在状态改变时允许其改变行为，这个对象看起来像改变了其类。

usage

● 结构清晰
避免了过多的switch…case或者if…else语句的使用，避免了程序的复杂性,提高系统的维护性。
● 遵循设计原则
很好地体现了开闭原则和单一职责原则，每个状态都是一个子类，你要增加状态就要增加子类，你要修改状态，你只修改一个子类就可以了。
● 封装性非常好
这也是状态模式的基本要求，状态变换放置到类的内部来实现，外部的调用不用知道类内部如何实现状态和行为的变换。

code


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(u"Scanning... Station is %s %s" %
              (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(u"Switching to FM")
        self.radio.state = self.radio.fmstate


class 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(u"Switching to AM")
        self.radio.state = self.radio.amstate


class 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 out
if __name__ == '__main__':
    radio = Radio()
    actions = [radio.scan] * 2 + [radio.toggle_amfm] + [radio.scan] * 2
    actions *= 2

    for action in actions:
        action()

### OUTPUT ###
# Scanning... Station is 1380 AM
# Scanning... Station is 1510 AM
# Switching to FM
# Scanning... Station is 89.1 FM
# Scanning... Station is 103.9 FM
# Scanning... Station is 81.3 FM
# Scanning... Station is 89.1 FM
# Switching to AM
# Scanning... Station is 1250 AM
# Scanning... Station is 1380 AM

设计模式-状态模式-state-python

def

usage

code

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