2:策略模式

class Strategy:

    def result(self,original):
        return print(original)

class NormalStrategy(Strategy):
    pass

class BargainStrategy(Strategy):
    def __init__(self,discount):
        self.discount = discount

    def result(self,original):
        return print(self.discount*original)

class CashBackStrategy(Strategy):

    def __init__(self,limit,back):
        self.limit = limit
        self.back = back

    def result(self,original):
        if(original>=self.limit):
            original -= self.back
        return print(original)

class Context():
    
    def __init__(self,classname):                             #对象实例化并且调用其方法
        self.classname = classname
        
    def GetResult(self,original):
        return print(self.classname.result(original))          #由于是普通方法，所以可以用类名来调用

original = int(input('输入原价：'))                              #对外仅仅暴露Context类
strategy = (input('请输入打折模式：(正常/8折/满300减100):'))
if(strategy =='正常'):
    Context(NormalStrategy()).GetResult(original)
elif(strategy == '8折'):
    Context(BargainStrategy(0.8)).GetResult(original)
if(strategy == '满300减100'):
    Context(CashBackStrategy(300,100)).GetResult(original)