updated from Atlas

10-dp-1class-func/strategy_best4.py

@@ -4,29 +4,32 @@
 # registered by a decorator
 
 """
+    >>> from decimal import Decimal
+    >>> from strategy import Customer, LineItem, Order
+    >>> from promotions import *
     >>> joe = Customer('John Doe', 0)
     >>> ann = Customer('Ann Smith', 1100)
-    >>> cart = [LineItem('banana', 4, .5),
-    ...         LineItem('apple', 10, 1.5),
-    ...         LineItem('watermelon', 5, 5.0)]
-    >>> Order(joe, cart, fidelity)
+    >>> cart = [LineItem('banana', 4, Decimal('.5')),
+    ...         LineItem('apple', 10, Decimal('1.5')),
+    ...         LineItem('watermelon', 5, Decimal(5))]
+    >>> Order(joe, cart, fidelity_promo)
     <Order total: 42.00 due: 42.00>
-    >>> Order(ann, cart, fidelity)
+    >>> Order(ann, cart, fidelity_promo)
     <Order total: 42.00 due: 39.90>
-    >>> banana_cart = [LineItem('banana', 30, .5),
-    ...                LineItem('apple', 10, 1.5)]
-    >>> Order(joe, banana_cart, bulk_item)
+    >>> banana_cart = [LineItem('banana', 30, Decimal('.5')),
+    ...                LineItem('apple', 10, Decimal('1.5'))]
+    >>> Order(joe, banana_cart, bulk_item_promo)
     <Order total: 30.00 due: 28.50>
-    >>> long_order = [LineItem(str(item_code), 1, 1.0)
+    >>> long_cart = [LineItem(str(item_code), 1, Decimal(1))
     ...               for item_code in range(10)]
-    >>> Order(joe, long_order, large_order)
+    >>> Order(joe, long_cart, large_order_promo)
     <Order total: 10.00 due: 9.30>
-    >>> Order(joe, cart, large_order)
+    >>> Order(joe, cart, large_order_promo)
     <Order total: 42.00 due: 42.00>
 
 # tag::STRATEGY_BEST_TESTS[]
 
-    >>> Order(joe, long_order, best_promo)
+    >>> Order(joe, long_cart, best_promo)
     <Order total: 10.00 due: 9.30>
     >>> Order(joe, banana_cart, best_promo)
     <Order total: 30.00 due: 28.50>
@@ -36,47 +39,16 @@
 # end::STRATEGY_BEST_TESTS[]
 """
 
-from collections import namedtuple
-from typing import Callable, List
-
-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:  # the Context
-    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):
-        return f'<Order total: {self.total():.2f} due: {self.due():.2f}>'
+from decimal import Decimal
+from typing import Callable
 
+from strategy import Order
 
 # tag::STRATEGY_BEST4[]
 
-Promotion = Callable[[Order], float]  # <2>
+Promotion = Callable[[Order], Decimal]
+
+promos: list[Promotion] = []  # <1>
 
 
 def promotion(promo: Promotion) -> Promotion:  # <2>
@@ -84,38 +56,35 @@ def promotion(promo: Promotion) -> Promotion:  # <2>
     return promo
 
 
-promos: List[Promotion] = []  # <1>
+def best_promo(order: Order) -> Decimal:
+    """Compute the best discount available"""
+    return max(promo(order) for promo in promos)  # <3>
 
 
-@promotion  # <3>
-def fidelity(order: Order) -> float:
+@promotion  # <4>
+def fidelity(order: Order) -> Decimal:
     """5% discount for customers with 1000 or more fidelity points"""
-    return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0
+    if order.customer.fidelity >= 1000:
+        return order.total() * Decimal('0.05')
+    return Decimal(0)
 
 
 @promotion
-def bulk_item(order: Order) -> float:
+def bulk_item(order: Order) -> Decimal:
     """10% discount for each LineItem with 20 or more units"""
-    discount = 0
+    discount = Decimal(0)
     for item in order.cart:
         if item.quantity >= 20:
-            discount += item.total() * 0.1
+            discount += item.total() * Decimal('0.1')
     return discount
 
 
 @promotion
-def large_order(order: Order) -> float:
+def large_order(order: Order) -> Decimal:
     """7% discount for orders with 10 or more distinct items"""
     distinct_items = {item.product for item in order.cart}
     if len(distinct_items) >= 10:
-        return order.total() * 0.07
-    return 0
-
-
-def best_promo(order: Order) -> float:  # <4>
-    """Select best discount available
-    """
-    return max(promo(order) for promo in promos)
-
+        return order.total() * Decimal('0.07')
+    return Decimal(0)
 
 # end::STRATEGY_BEST4[]