详解Python设计模式之策略模式

from abc import ABC, abstractmethod
from collections import namedtuple

Customer = namedtuple('Customer', 'name fidelity')


class LineItem:
 """订单中单个商品的数量和单价"""
 def __init__(self, product, quantity, price):
 self.product = product
 self.quantity = quantity
 self.price = price

 def total(self):
 return self.price * self.quantity


class Order:
 """订单"""
 def __init__(self, customer, cart, promotion=None):
 self.customer = customer
 self.cart = list(cart)
 self.promotion = promotion

 def total(self):
 if not hasattr(self, '__total'):
  self.__total = sum(item.total() for item in self.cart)
 return self.__total

 def due(self):
 if self.promotion is None:
  discount = 0
 else:
  discount = self.promotion.discount(self)
 return self.total() - discount

 def __repr__(self):
 fmt = '<订单 总价: {:.2f} 实付: {:.2f}>'
 return fmt.format(self.total(), self.due())


class Promotion(ABC): # 策略：抽象基类
 @abstractmethod
 def discount(self, order):
 """返回折扣金额（正值）"""


class FidelityPromo(Promotion): # 第一个具体策略
 """为积分为1000或以上的顾客提供5%折扣"""
 def discount(self, order):
 return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0


class BulkItemPromo(Promotion): # 第二个具体策略
 """单个商品为20个或以上时提供10%折扣"""
 def discount(self, order):
 discount = 0
 for item in order.cart:
  if item.quantity >= 20:
  discount += item.total() * 0.1
 return discount


class LargeOrderPromo(Promotion): # 第三个具体策略
 """订单中的不同商品达到10个或以上时提供7%折扣"""
 def discount(self, order):
 distinct_items = {item.product for item in order.cart}
 if len(distinct_items) >= 10:
  return order.total() * 0.07
 return 0


joe = Customer('John Doe', 0)
ann = Customer('Ann Smith', 1100)

cart = [LineItem('banana', 4, 0.5),
 LineItem('apple', 10, 1.5),
 LineItem('watermellon', 5, 5.0)]

print('策略一：为积分为1000或以上的顾客提供5%折扣')
print(Order(joe, cart, FidelityPromo()))
print(Order(ann, cart, FidelityPromo()))

banana_cart = [LineItem('banana', 30, 0.5),
  LineItem('apple', 10, 1.5)]

print('策略二：单个商品为20个或以上时提供10%折扣')
print(Order(joe, banana_cart, BulkItemPromo()))

long_order = [LineItem(str(item_code), 1, 1.0) for item_code in range(10)]

print('策略三：订单中的不同商品达到10个或以上时提供7%折扣')
print(Order(joe, long_order, LargeOrderPromo()))
print(Order(joe, cart, LargeOrderPromo()))

from collections import namedtuple

Customer = namedtuple('Customer', 'name fidelity')


class LineItem:
 def __init__(self, product, quantity, price):
 self.product = product
 self.quantity = quantity
 self.price = price

 def total(self):
 return self.price * self.quantity


class Order:
 def __init__(self, customer, cart, promotion=None):
 self.customer = customer
 self.cart = list(cart)
 self.promotion = promotion

 def total(self):
 if not hasattr(self, '__total'):
  self.__total = sum(item.total() for item in self.cart)
 return self.__total

 def due(self):
 if self.promotion is None:
  discount = 0
 else:
  discount = self.promotion(self)
 return self.total() - discount

 def __repr__(self):
 fmt = '<订单 总价: {:.2f} 实付: {:.2f}>'
 return fmt.format(self.total(), self.due())


def fidelity_promo(order):
 """为积分为1000或以上的顾客提供5%折扣"""
 return order.total() * .05 if order.customer.fidelity >= 1000 else 0


def bulk_item_promo(order):
 """单个商品为20个或以上时提供10%折扣"""
 discount = 0
 for item in order.cart:
 if item.quantity >= 20:
  discount += item.total() * .1
 return discount


def large_order_promo(order):
 """订单中的不同商品达到10个或以上时提供7%折扣"""
 distinct_items = {item.product for item in order.cart}
 if len(distinct_items) >= 10:
 return order.total() * .07
 return 0


joe = Customer('John Doe', 0)
ann = Customer('Ann Smith', 1100)

cart = [LineItem('banana', 4, 0.5),
 LineItem('apple', 10, 1.5),
 LineItem('watermellon', 5, 5.0)]

print('策略一：为积分为1000或以上的顾客提供5%折扣')
print(Order(joe, cart, fidelity_promo))
print(Order(ann, cart, fidelity_promo))

banana_cart = [LineItem('banana', 30, 0.5),
  LineItem('apple', 10, 1.5)]

print('策略二：单个商品为20个或以上时提供10%折扣')
print(Order(joe, banana_cart, bulk_item_promo))

long_order = [LineItem(str(item_code), 1, 1.0) for item_code in range(10)]

print('策略三：订单中的不同商品达到10个或以上时提供7%折扣')
print(Order(joe, long_order, large_order_promo))
print(Order(joe, cart, large_order_promo))