Python 设计模式 - 状态模式

• 

  简述

  它为状态机提供了一个模块，这些状态机是使用从指定状态机类派生的子类实现的。这些方法与状态无关，并导致使用装饰器声明的转换。
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  如何实现状态模式？

  状态模式的基本实现如下所示 -

  
  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

  上述程序生成以下输出 -