状态模式的理解

允许一个对象在其内部状态改变时改变它的行为。对象看起来似乎修改了它的类

现实碰到例子

收音机 am fm 的切换
山地车的调速
地铁的人员调控(当时间段到时行为好像变化了)
节假日改变
一个人的状态在积极和消极是不同的

实例

对象包含状态
状态能够切换
状态最好能够是继承
状态行为最好一致

from __future__ import print_function

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.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("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()

参考

python-patterns