Python: Strategy Pattern

 GeovinDuStrategy.py

# 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

# 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：

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