91 lines
2.6 KiB
Python
91 lines
2.6 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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>>> from decimal import Decimal
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>>> from strategy import Customer, LineItem, Order
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>>> from promotions import *
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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, Decimal('.5')),
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... LineItem('apple', 10, Decimal('1.5')),
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... LineItem('watermelon', 5, Decimal(5))]
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>>> Order(joe, cart, fidelity_promo)
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<Order total: 42.00 due: 42.00>
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>>> Order(ann, cart, fidelity_promo)
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<Order total: 42.00 due: 39.90>
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>>> banana_cart = [LineItem('banana', 30, Decimal('.5')),
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... LineItem('apple', 10, Decimal('1.5'))]
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>>> Order(joe, banana_cart, bulk_item_promo)
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<Order total: 30.00 due: 28.50>
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>>> long_cart = [LineItem(str(item_code), 1, Decimal(1))
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... for item_code in range(10)]
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>>> Order(joe, long_cart, large_order_promo)
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<Order total: 10.00 due: 9.30>
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>>> Order(joe, cart, large_order_promo)
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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_cart, 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 decimal import Decimal
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from typing import Callable
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from strategy import Order
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# tag::STRATEGY_BEST4[]
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Promotion = Callable[[Order], Decimal]
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promos: list[Promotion] = [] # <1>
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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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def best_promo(order: Order) -> Decimal:
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"""Compute the best discount available"""
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return max(promo(order) for promo in promos) # <3>
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@promotion # <4>
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def fidelity(order: Order) -> Decimal:
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"""5% discount for customers with 1000 or more fidelity points"""
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if order.customer.fidelity >= 1000:
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return order.total() * Decimal('0.05')
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return Decimal(0)
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@promotion
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def bulk_item(order: Order) -> Decimal:
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"""10% discount for each LineItem with 20 or more units"""
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discount = Decimal(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() * Decimal('0.1')
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return discount
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@promotion
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def large_order(order: Order) -> Decimal:
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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() * Decimal('0.07')
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return Decimal(0)
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# end::STRATEGY_BEST4[]
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