122 lines
3.2 KiB
Python
122 lines
3.2 KiB
Python
# strategy_best4.py
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# Strategy pattern -- function-based implementation
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# selecting best promotion from list of functions
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# registered by a decorator
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"""
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>>> joe = Customer('John Doe', 0)
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>>> ann = Customer('Ann Smith', 1100)
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>>> cart = [LineItem('banana', 4, .5),
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... LineItem('apple', 10, 1.5),
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... LineItem('watermelon', 5, 5.0)]
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>>> Order(joe, cart, fidelity)
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<Order total: 42.00 due: 42.00>
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>>> Order(ann, cart, fidelity)
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<Order total: 42.00 due: 39.90>
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>>> banana_cart = [LineItem('banana', 30, .5),
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... LineItem('apple', 10, 1.5)]
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>>> Order(joe, banana_cart, bulk_item)
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<Order total: 30.00 due: 28.50>
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>>> long_order = [LineItem(str(item_code), 1, 1.0)
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... for item_code in range(10)]
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>>> Order(joe, long_order, large_order)
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<Order total: 10.00 due: 9.30>
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>>> Order(joe, cart, large_order)
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<Order total: 42.00 due: 42.00>
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# tag::STRATEGY_BEST_TESTS[]
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>>> Order(joe, long_order, best_promo)
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<Order total: 10.00 due: 9.30>
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>>> Order(joe, banana_cart, best_promo)
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<Order total: 30.00 due: 28.50>
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>>> Order(ann, cart, best_promo)
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<Order total: 42.00 due: 39.90>
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# end::STRATEGY_BEST_TESTS[]
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"""
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from collections import namedtuple
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from typing import Callable, List
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Customer = namedtuple('Customer', 'name fidelity')
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class LineItem:
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def __init__(self, product, quantity, price):
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self.product = product
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self.quantity = quantity
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self.price = price
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def total(self):
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return self.price * self.quantity
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class Order: # the Context
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def __init__(self, customer, cart, promotion=None):
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self.customer = customer
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self.cart = list(cart)
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self.promotion = promotion
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def total(self):
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if not hasattr(self, '__total'):
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self.__total = sum(item.total() for item in self.cart)
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return self.__total
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def due(self):
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if self.promotion is None:
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discount = 0
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else:
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discount = self.promotion(self)
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return self.total() - discount
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def __repr__(self):
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return f'<Order total: {self.total():.2f} due: {self.due():.2f}>'
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# tag::STRATEGY_BEST4[]
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Promotion = Callable[[Order], float] # <2>
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def promotion(promo: Promotion) -> Promotion: # <2>
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promos.append(promo)
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return promo
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promos: List[Promotion] = [] # <1>
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@promotion # <3>
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def fidelity(order: Order) -> float:
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"""5% discount for customers with 1000 or more fidelity points"""
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return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0
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@promotion
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def bulk_item(order: Order) -> float:
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"""10% discount for each LineItem with 20 or more units"""
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discount = 0
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for item in order.cart:
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if item.quantity >= 20:
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discount += item.total() * 0.1
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return discount
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@promotion
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def large_order(order: Order) -> float:
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"""7% discount for orders with 10 or more distinct items"""
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distinct_items = {item.product for item in order.cart}
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if len(distinct_items) >= 10:
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return order.total() * 0.07
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return 0
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def best_promo(order: Order) -> float: # <4>
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"""Select best discount available
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"""
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return max(promo(order) for promo in promos)
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# end::STRATEGY_BEST4[]
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