# Filename : example.py
# Copyright : 2020 By Bianchenghao6
# Author by : bianchenghao6.com
# 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)
 

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