策略模式
from abc import ABC, abstractclassmethod
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 = 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 = '<Order total: {:.2f}> due: {:.2f}>'
return fmt.format(self.total(), self.due())
class Promotion(ABC):
@abstractclassmethod
def discount(self, order):
""" 返回折扣金额（非负数） """
class FidelityPromo(Promotion):
""" 为积分为1000或以上的顾客提供5%的折扣 """
def discount(self, order):
return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0
class BulkltemPromo(Promotion):
""" 单个商品为20个或以上是提供10%折扣 """
def discount(self, order):
discount = 0
for item in order.cart:
if item.quantity >= 20:
discount += item.total() * 0.01
return discount
class LargeOrderPromo(Promotion):
""" 订单中不同商品达到10个或以上时提供7%折扣 """
def discount(self, order):
discount_items = {item.product for item in order.cart}
if len(discount_items) >= 10:
return order.total() * 0.07
return 0
行为参数化
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 = 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 = '<Order total: {:.2f}> due: {:.2f}>'
return fmt.format(self.total(), self.due())
def fidelity_promo(order: Order):
""" 为积分为1000或以上的顾客提供5%的折扣 """
return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0
def bulkltem_promo(order: Order):
""" 单个商品为20个或以上是提供10%折扣 """
discount = 0
for item in order.cart:
if item.quantity >= 20:
discount += item.total() * 0.01
return discount
def large_order_promo(order: Order):
""" 订单中不同商品达到10个或以上时提供7%折扣 """
discount_items = {item.product for item in order.cart}
if len(discount_items) >= 10:
return order.total() * 0.07
return 0
优化
自动选择最佳折扣
将所有折扣函数放在另一个文件中
# file: promotions.py
from strategy import Order
def fidelity_promo(order: Order):
""" 为积分为1000或以上的顾客提供5%的折扣 """
return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0
def bulkltem_promo(order: Order):
""" 单个商品为20个或以上是提供10%折扣 """
discount = 0
for item in order.cart:
if item.quantity >= 20:
discount += item.total() * 0.01
return discount
def large_order_promo(order: Order):
""" 订单中不同商品达到10个或以上时提供7%折扣 """
discount_items = {item.product for item in order.cart}
if len(discount_items) >= 10:
return order.total() * 0.07
return 0
添加一个自动获取最佳折扣的函数
from collections import namedtuple
import promotions
import inspect
# inspect.getmembers() 获取模块中的对象
# 第一个参数是模块名，第二个参数是筛选条件
# inspect.isfunction 判断对象是否是函数
promos = [func for name, func in inspect.getmembers(
promotions, inspect.isfunction)]
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 = 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 = '<Order total: {:.2f}> due: {:.2f}>'
return fmt.format(self.total(), self.due())
def best_promo(order: Order):
""" 自动选择可用的最佳折扣 """
return max(promos(order) for promos in promos)
通过以上优化，不仅可以自动选择最佳折扣，如果想添加其他折扣规则，只需要在 promotions.py 文件中添加函数就可以了，不用改动其他的代码。
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