Python状态模式

标签： python 设计模式

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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

状态图.png-37kB
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

状态图2.png-42.4kB
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

状态图3.png-50.9kB
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

执行图.png-59.2kB
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