python状态模式

标签： python 设计模式

引子

状态模式确实很好玩，我是说书上的例子确实很好玩，我对着电脑玩了好长时间，但是想说清楚还真不太容易，先从容易的开始吧

糖果机

糖果机操作的流程如下所示，这张图也叫状态图，它显示了糖果机的工作流程及状态流程
状态图1

其中一共有四个状态

售出糖果
糖果售罄
有25分钱
没有25分钱
操作糖果机会设计四个动作
投入25分钱
退回25分钱
转动曲柄

发放糖果这个动作是糖果机内部的动作，机器自己调用

一开始...

创建一个糖果机的类，包含了四种状态

class GumballMachine:
def __init__(self, count):
    self.SOLD_OUT = 0   #糖果售罄状态
    self.NO_QUARTER = 1 #没有25分钱状态
    self.HAS_QUARTER = 2    #有25分钱状态
    self.SOLD = 3   #售出糖果状态
    self.state = self.SOLD_OUT  #初始状态为`没有25分钱状态`
    self.count = count  #设置一个糖果数量变量，它为0时就是糖果售罄的状态
    if self.count > 0:  #此处如果糖果数大于0，则状态为初始状态
 self.state = self.NO_QUARTER


接下来该怎么办呢？

按照上图，状态与状态之间是通过动作进行连接的，可以对每一个动作创建一个对应的方法，这些方法利用条件语句来决定在四个状态下的恰当行为

例如投入25分钱和这个动作在四种状态下糖果机的反应如下图
状态图2


动作代表当前执行的动作是投入25分钱

如果糖果机当前状态是没有25分钱，则糖果机行为是显示你投入了25分钱，之后状态要切换到有25分钱

如果糖果机当前状态是有25分钱，则糖果机行为是显示投多了

如果糖果机当前状态是糖果售罄，则糖果机行为是显示售光了，不能投了

如果糖果机当前状态是售出糖果，则糖果机行为是显示投太快了，稍等，因为售出糖果后，糖果机要恢复到初始状态没有25分钱

剩下的动作和这个没有什么区别，每个动作都有一个状态转换的步骤
代码
def insertQuarter(self):    #投入25分钱动作
    if self.state == self.HAS_QUARTER:
 print("You cannot insert another quarter")
    elif self.state == self.NO_QUARTER:
 self.state = self.HAS_QUARTER
 print("You insert a quarter")
    elif self.state == self.SOLD_OUT:
 print("You can't insert a quarter, the machine is sold out")
    elif self.state == self.SOLD:
 print("Please wait, we're already giving you a gumball")

def ejectQuarter(self):     #退回25分钱动作
    if self.state == self.HAS_QUARTER:
 print("Quarter returned")
 self.state = self.NO_QUARTER
    elif self.state == self.NO_QUARTER:
 print("You haven't inserted a quarter")
    elif self.state == self.SOLD:
 print("Sorry, you already turned the crank")
    elif self.state == self.SOLD_OUT:
 print("You can't eject, you haven't inserted a quarter yet")

def turnCrank(self):    #转动曲柄动作
    if self.state == self.SOLD:
 print("Turning twice doesn't get you another gumball!")
    elif self.state == self.NO_QUARTER:
 print("You turned, but there's no quarter")
    elif self.state == self.SOLD_OUT:
 print("You turned, but there's no gumball")
    elif self.state == self.HAS_QUARTER:
 print("You turned....")
 self.state = self.SOLD
 self.dispense()     #切换到发放糖果这个内部动作上

def dispense(self):     #发放糖果动作
    if self.state == self.SOLD:
 print("A gumball comes rolling out the slot")
 self.count = self.count - 1     #发放一次糖果，糖果数量要减1
 if self.count == 0:    #糖果数量为0了，切换到糖果售罄的状态
     print("Oops, out of gumballs")
     self.state = self.SOLD_OUT
 else:
     self.state = self.NO_QUARTER
    elif self.state == self.NO_QUARTER:
 print("You need to pay first")
    elif self.state == self.SOLD_OUT:
 print("No gumball dispense")
    elif self.state == self.HAS_QUARTER:
 print("No gumball dispense")

玩一玩....

可以增加两个方法，玩的时候实时查看当前状态和糖果数量
def getCount(self):
    print(self.count)
def getState(self):
    print(self.state)

按照下面方法玩
def main():
gumballMachine = GumballMachine(2)
gumballMachine.getCount()
gumballMachine.getState()
print("=====================================================")
gumballMachine.insertQuarter()
gumballMachine.getState()
gumballMachine.ejectQuarter()
gumballMachine.ejectQuarter()
gumballMachine.insertQuarter()
gumballMachine.getState()
gumballMachine.turnCrank()
gumballMachine.getState()
gumballMachine.getCount()
gumballMachine.insertQuarter()
gumballMachine.turnCrank()
gumballMachine.getState()
print("=====================================================")
gumballMachine.turnCrank()

返回的结果
2   #两个糖果
1   #没有25分钱状态
=====================================================
You insert a quarter
2   #有25分钱状态
Quarter returned
You haven't inserted a quarter
You insert a quarter
2   #有25分钱状态
You turned....
A gumball comes rolling out the slot
1   #没有25分钱状态
1   #一个糖果
You insert a quarter
You turned....
A gumball comes rolling out the slot
Oops, out of gumballs
0   #糖果售罄状态
=====================================================
You turned, but there's no gumball

这个时候如果又来了一个状态怎么办...

按照状态2图，需要增加一个新的状态，之后在每个动作里面增加针对这个状态的行为，好像违反了好多设计原则。
新的方法
状态是变化的量，将变化封装起来，将动作和行为放到状态里，这样每个状态只要实现它自己的那套行为。

为每个状态创建状态类，这些类负责在对应的动作下糖果机的行为

将动作和行为委托给状态类

状态图3 之前的状态图2现在要变成这样了，用状态包裹所有的动作及对应的行为有25分钱状态下，每一个动作对应不同的行为，在执行退回25钱动作后，状态切换到没有25分钱状态，在执行转动曲柄动作后，状态切换到没有25分钱状态。代码先看状态图3的代码实现


#有25分钱状态
class HasQuarterState(object):
    def __init__(self, gumballMachine): #传入糖果机的实例
 self.gumballMachine = gumballMachine
    def insertQuarter(self):    #投入25分钱动作
 print("You cannot insert another quarter")
    def ejectQuarter(self):     #退出25分钱动作
 print("Quarter returned")
 self.gumballMachine.setState(self.gumballMachine.getNoQuarterState())   #之后糖果机的状
 #态切换到没有25分钱状态
    def turnCrank(self):    #转动曲柄动作
 print("You turned....")
 self.gumballMachine.setState(self.gumballMachine.getSoldState())    #之后糖果机的状
 #态切换到售出糖果状态
    def dispense(self):     #发放糖果动作，这是个内部动作，此处实现没有作用
 print("No gumball dispense")

其他状态的代码也是类似
#糖果售罄状态
class SoldOutState(object):
    def __init__(self, gumballMachine):
 self.gumballMachine = gumballMachine
    def insertQuarter(self):
 print("You can't insert a quarter, the machine is sold out")
    def ejectQuarter(self):
 print("You can't eject, you haven't inserted a quarter yet")
    def turnCrank(self):
 print("You turned, but there's no gumball")
    def dispense(self):
 print("No gumball dispense")
#没有25分钱状态
class NoQuarterState(object):
    def __init__(self, gumballMachine):
 self.gumballMachine = gumballMachine
    def insertQuarter(self):
 print("You inserted a quarter")
 self.gumballMachine.setState(self.gumballMachine.getHasQuarterState())
    def ejectQuarter(self):
 print("You haven't inserted a quarter")
    def turnCrank(self):
 print("You turned, but there's no quarter")
    def dispense(self):
 print("You need to pay first")
#售出糖果状态 
class SoldState(object):
    def __init__(self, gumballMachine):
 self.gumballMachine = gumballMachine
    def insertQuarter(self):
 print("Please wait, we're already giving you a gumball")
    def ejectQuarter(self):
 print("Sorry, you already turned the crank")
    def turnCrank(self):
 print("Turning twice doesn't get you another gumball!")
    def dispense(self):
 self.gumballMachine.releaseBall()
 if self.gumballMachine.getCount()>0:
     self.gumballMachine.setState(self.gumballMachine.getNoQuarterState())
 else:
     print("Oops, out of gumballs")
     self.gumballMachine.setState(self.gumballMachine.getSoldOutState())

看看糖果机的实现
#糖果机类
class GumballMachine:
    def __init__(self, numberGumballs):
 self.count = numberGumballs
#=========创建每一个状态的状态实例====================#
 self.soldOutState = SoldOutState(self)
 self.noQuarterState = NoQuarterState(self)
 self.hasQuarterState = HasQuarterState(self)
 self.soldState = SoldState(self)
#=========end=========================================#
 if self.count > 0:
     self.state = self.noQuarterState
#============每个状态的get方法和set方法===============#
    def getSoldOutState(self):
 return self.soldOutState
    def getNoQuarterState(self):
 return self.noQuarterState
    def getHasQuarterState(self):
 return self.hasQuarterState
    def getSoldState(self):
 return self.soldState
    def setState(self, state):
 self.state = state
#=========end=========================================#
#============将方法委托给当前的状态===================#
    def insertQuarter(self):
 self.state.insertQuarter()
    def ejectQuarter(self):
 self.state.ejectQuarter()
    def turnCrank(self):
 if self.state == self.hasQuarterState:
     self.state.turnCrank()
     self.state.dispense()
 else:
     self.state.turnCrank()
#=========end=========================================#
    def releaseBall(self):
 print("A gumball comes rolling out the slot...")
 if self.count != 0:
     self.count -= 1
#============检查状态和糖果数量的方法=================#
    def getState(self):
 print(self.state)
    def getCount(self):
 return self.count

还是用之前得测试代码，看看返回
2   #糖果数量
<__main__.NoQuarterState object at 0x01D6BC90>      #当前状态
=====================================================
You inserted a quarter      #行为
<__main__.HasQuarterState object at 0x01D6BCB0>     #当前状态
Quarter returned #行为
You haven't inserted a quarter      #行为
You inserted a quarter      #行为
<__main__.HasQuarterState object at 0x01D6BCB0>     #当前状态
You turned....      #行为
A gumball comes rolling out the slot...     #行为
<__main__.NoQuarterState object at 0x01D6BC90>      #当前状态
1#糖果数量
You inserted a quarter      #行为
You turned....      #行为
A gumball comes rolling out the slot...     #行为
Oops, out of gumballs#行为
<__main__.SoldOutState object at 0x01D6BC70> #当前状态
=====================================================
You turned, but there's no gumball      #行为

看看执行图


初始状态是没有25分钱，执行投入25分钱动作

糖果机切换状态到第二步状态有25分钱，之后执行转动曲柄动作

糖果机切换状态到第三步状态售出糖果，之后执行发放糖果动作

如果糖果数目为0，则糖果机切换状态到第四步状态糖果售罄

糖果机动作和行为都委托给了每种状态，状态一变，糖果机的行为就是此种状态下的动作产生的行为了，这样一来，如果增加了一种状态，只要单独实现这个状态下糖果机所有的行为就OK了。
再来一个状态
增加一个游戏状态，转曲柄获取糖果的时候，有10%的机会能成为大赢家，获得附赠的一粒糖果，这个怎么搞？

增加一个状态winnerState
class WinnerState(object):
    def __init__(self, gumballMachine):
 self.gumballMachine = gumballMachine
    def insertQuarter(self):
 print("Please wait, we're already giving you a gumball")
    def ejectQuarter(self):
 print("Sorry, you already turned the crank")
    def turnCrank(self):
 print("Turning twice doesn't get you another gumball!")
    # 你赢了，如果糖果没了，那就算了，只能白赢了；
    def dispense(self):
 print("You are winner! You get 2 gumball for youe quarter")
 if self.gumballMachine.getCount()==0:
     self.gumballMachine.setState(self.gumballMachine.getSoldOutState())
 else:
     self.gumballMachine.releaseBall()
     if self.gumballMachine.getCount()>0:
  self.gumballMachine.releaseBall()
  self.gumballMachine.setState(self.gumballMachine.getNoQuarterState())
     else:
  print("Oops, out of gumballs")
  self.gumballMachine.setState(self.gumballMachine.getSoldOutState())

随机数怎么整，random.randint这个就能实现，但是这个动作要增加在哪里呢，哪个状态下转动曲柄可以获得糖果，是有25分钱这个状态，只要将这个状态下的转曲柄动作稍微改动一下就OK了
def turnCrank(self):
 print("You turned....")
 #产生随机数
 self.winner = random.randint(1, 100)
 #这个数为1你就赢了
 if self.winner == 1:
     self.gumballMachine.setState(self.gumballMachine.getWinnerState())
 else:
     self.gumballMachine.setState(self.gumballMachine.getSoldState())

开始玩吧
def main():
    gumballMachine = GumballMachine(100)
    print(gumballMachine.getCount())
    for i in range(5):
 print("======================{0}====================".format(i+1))
 gumballMachine.insertQuarter()
 gumballMachine.turnCrank()
    print(gumballMachine.getCount())

5次几率好像太小，应该中不了
======================1====================
You inserted a quarter
You turned....
You are winner! You get 2 gumball for youe quarter
A gumball comes rolling out the slot...
A gumball comes rolling out the slot...
======================2====================
You inserted a quarter
You turned....
A gumball comes rolling out the slot...
======================3====================
You inserted a quarter
You turned....
A gumball comes rolling out the slot...
======================4====================
You inserted a quarter
You turned....
A gumball comes rolling out the slot...
======================5====================
You inserted a quarter
You turned....
A gumball comes rolling out the slot...
94

靠！！！！！第一次就中了
定义

状态模式允许对象在内部状态改变时改变它的行为，对象看起来好像修改了它的类

python状态模式

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