Python: Strategy Pattern

 GeovinDuStrategy.py

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# 策略模式  Strategy Pattern Types of trading strategies: class RiskyTradingStrategy(object):     def MakeTrades(self):         print("进行高风险交易!")     class ModerateTradingStrategy(object):     def MakeTrades(self):         print("进行适度的交易.")     class ConservativeTradingStrategy(object):     def MakeTrades(self):         print("进行安全交易.")     # Not Supported below Python 3.4! from enum import Enum     class TradeConditions(Enum):     BearMarket = 0,     BullMarket = 1,     RecoveringMarket = 2     # The trading firm which changes strategies based on market conditions: class TradingFirm(object):     def __init__(self):         self.riskyStrategy = RiskyTradingStrategy()         self.moderateStrategy = ModerateTradingStrategy()         self.safeStrategy = ConservativeTradingStrategy()           self.currentStrategy = self.moderateStrategy       def MarketUpdte(self, tradeConditions):         # Select the best strategy for the market conditions:         if tradeConditions == TradeConditions.BearMarket:             self.currentStrategy = self.safeStrategy         elif tradeConditions == TradeConditions.BullMarket:             self.currentStrategy = self.riskyStrategy         elif tradeConditions == TradeConditions.RecoveringMarket:             self.currentStrategy = self.moderateStrategy           # Make trades with that strategy:         self.currentStrategy.MakeTrades()     class Item:     """Constructor function with price and discount"""       def __init__(self, price, discount_strategy=None):           """take price and discount strategy"""           self.price = price         self.discount_strategy = discount_strategy       """A separate function for price after discount"""       def price_after_discount(self):           if self.discount_strategy:             discount = self.discount_strategy(self)         else:             discount = 0           return self.price - discount       def __repr__(self):           statement = "价格: {}, 折扣后的价格: {}"         return statement.format(self.price, self.price_after_discount())     """function dedicated to On Sale Discount"""     def on_sale_discount(order):     return order.price * 0.25 + 20     """function dedicated to 20 % discount"""     def twenty_percent_discount(order):     return order.price * 0.20

　　

main.py 调用

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# 策略模式  Strategy Pattern higeovindu=GeovinDuStrategy.TradingFirm() higeovindu.MarketUpdte(higeovindu.moderateStrategy.MakeTrades()) higeovindu.safeStrategy.MakeTrades() higeovindu.currentStrategy.MakeTrades() higeovindu.riskyStrategy.MakeTrades()   print(GeovinDuStrategy.Item(20000))   """with discount strategy as 20 % discount""" print(GeovinDuStrategy.Item(20000, discount_strategy=GeovinDuStrategy.twenty_percent_discount))   """with discount strategy as On Sale Discount""" print(GeovinDuStrategy.Item(20000, discount_strategy=GeovinDuStrategy.on_sale_discount))

　　

输出：

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进行适度的交易. 进行适度的交易. 进行安全交易. 进行适度的交易. 进行高风险交易! 价格: 20000, 折扣后的价格: 20000 价格: 20000, 折扣后的价格: 16000.0 价格: 20000, 折扣后的价格: 14980.0