代码里我们经常会出现大量的条件判断，在这种情况下，我们可以实现状态机避免过度使用

有一种方式是把各种状态归为各种状态类

还有一种方式是修改实例的__class__属性

"""
状态机的实现
修改实例的__class__属性
"""


class Connection:
    def __init__(self):
        self.new_state(CloseState)

    def new_state(self, state):
        self.__class__ = state

    def read(self):
        raise NotImplementedError

    def write(self, data):
        raise NotImplementedError

    def open(self):
        raise NotImplementedError

    def close(self):
        raise NotImplementedError


class CloseState(Connection):
    def read(self):
        raise RuntimeError("Not Open")

    def write(self, data):
        raise RuntimeError("Not Open")

    def open(self):
        self.new_state(OpenState)

    def close(self):
        raise RuntimeError("Already close")


class OpenState(Connection):
    def read(self):
        print("reading")

    def write(self, data):
        print("writing")

    def open(self):
        raise RuntimeError("Already open")

    def close(self):
        self.new_state(CloseState)


if __name__ == "__main__":
    c = Connection()
    print(c)
    c.open()
    print(c)
    c.read()
    c.close()
    print(c)

output:

　　<__main__.CloseState object at 0x00000253645A1F10>
　　<__main__.OpenState object at 0x00000253645A1F10>
　　reading
　　<__main__.CloseState object at 0x00000253645A1F10>

具体的应用场景目前我在工作中还没有用到，后面我得注意下