Python 设计模式--策略模式

　　策略模式（Strategy Pattern）

　　策略模式是一种与行为相关的设计模式，允许你在运行时根据指定的上下文确定程序的动作。可以在两个类中封装不同的算法，并且在程序运行时确定到底执行哪中策略。

　　特点：定义算法家族，分别封装起来，让它们之间可以互相替换。此模式让算法的变化不会影响到使用算法的客户。

　　《大话设计模式》中实例：超市收银软件。

　　代码：

#!/usr/bin/env python
#-*- coding: utf-8 -*-

class CashSuper():
    def acceptCash(self):
        pass


class CashNormal(CashSuper):
    def accept(slef,money):
        return money

class CashRebate(CashSuper):
    moneyRebate = 0.0
    def __init__(self,rebate):
        self.moneyRebate = rebate
    def acceptCash(self,money):
        return money*self.moneyRebate

class CashReturn(CashSuper):
    m_moneyCondition = 0.0
    m_moneyReturn = 0.0

    def __init__(self,moneyCondition,moneyReturn):
        self.m_moneyCondition = moneyCondition
        self.m_moneyReturn = moneyReturn

    def acceptCash(self,money):
        if(money>self.m_moneyCondition):
            result = money - (money/self.m_moneyCondition)*self.m_moneyReturn
        else:
            result = money
        return result

class CashContext():
    def __init__(self,choice):
        self.s_cash = choice
    def getCash(self,money):
        return self.s_cash.acceptCash(money)


if __name__ == "__main__":
    money = input("Enter the money:")
    strategy = {}
    strategy[1] = CashContext(CashNormal)
    strategy[2] = CashContext(CashRebate)
    strategy[3] = CashContext(CashReturn(300,100))

    cash_type = input("Type: [1]for normal; [2]for 80% discount; [3]for 300 - 100.")

    if(cash_type in strategy.keys()):
        cash_strategy = strategy[cash_type]
    else:
        print(u"未定义的收费模式！使用正常收费！")
        cash_strategy = strategy[1]
    real_money = cash_strategy.getCash(money)

    print(u"实际付款：" + str(real_money))
    #print("实际付款：%d"%real_money)

　　步骤：

　　1、定义Strategy类，定义所有支持的算法的公共接口

　　2、定义ConcreteStrategy类，封装具体的算法或方法，继承于Strategy类

　　3、定义Context类，用一个ConcreteStrategy来配置，维护一个对Strategy对象的引用。

#!/usr/bin/env python
#-*- coding: utf-8 -*-

class Strategy():
    def AlgorithmInterface(self):
        pass

class ConcrateStrategyA(Strategy):
    def AlgorithmInterface(self):
        print("算法A实现！")


class ConcrateStrategyB(Strategy):
    def AlgorithmInterface(self):
        print("算法B实现！")


class ConcrateStrategyC(Strategy):
    def AlgorithmInterface(self):
        print("算法C实现！")

class Context():
    def __init__(self,choice):
        self.contextsuper = choice
        
    def ContextInterface(self):
        self.contextsuper.AlgorithmInterface()


if __name__ == "__main__":
    context = Context(ConcrateStrategyA())
    context.ContextInterface()

    context = Context(ConcrateStrategyB())
    context.ContextInterface()

    context = Context(ConcrateStrategyC())
    context.ContextInterface()