Python 状态模式

它为状态机提供了一个模块，该模块使用从指定状态机类派生的子类实现。这些方法与状态无关，并导致使用装饰器声明转换。

如何实现状态模式？

状态模式的基本实现如下所示：

# Filename : example.py
# Date : 2020-08-22
class ComputerState(object):
    name = "state"
    allowed = []
    def switch(self, state):
        """ Switch to new state """
        if state.name in self.allowed:
            print('Current:',self,' => switched to new state',state.name)
            self.__class__ = state
        else:
            print('Current:',self,' => switching to',state.name,'not possible.')
    def __str__(self):
        return self.name
class Off(ComputerState):
    name = "off"
    allowed = ['on']
class On(ComputerState):
    """ State of being powered on and working """
    name = "on"
    allowed = ['off','suspend','hibernate']
class Suspend(ComputerState):
    """ State of being in suspended mode after switched on """
    name = "suspend"
    allowed = ['on']
class Hibernate(ComputerState):
    """ State of being in hibernation after powered on """
    name = "hibernate"
    allowed = ['on']
class Computer(object):
    """ A class representing a computer """
    def __init__(self, model='HP'):
        self.model = model
        # State of the computer - default is off.
        self.state = Off()
    def change(self, state):
        """ Change state """
        self.state.switch(state)
if __name__ == "__main__":
    comp = Computer()
    comp.change(On)
    comp.change(Off)
    comp.change(On)
    comp.change(Suspend)
    comp.change(Hibernate)
    comp.change(On)
    comp.change(Off)

输出

上面的程序生成以下输出：

Current: off => switched to new state on
Current: on => switched to new state off
Current: off => switched to new state on
Current: on => switched to new state suspend
Current: suspend => switching to hibernate not possible.
Current: suspend => switched to new state on
Current: on => switched to new state off