updated from Atlas

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

@@ -6,20 +6,20 @@
 
     >>> joe = Customer('John Doe', 0)  # <1>
     >>> ann = Customer('Ann Smith', 1100)
-    >>> cart = [LineItem('banana', 4, .5),  # <2>
-    ...         LineItem('apple', 10, 1.5),
-    ...         LineItem('watermelon', 5, 5.0)]
+    >>> cart = (LineItem('banana', 4, Decimal('.5')),  # <2>
+    ...         LineItem('apple', 10, Decimal('1.5')),
+    ...         LineItem('watermelon', 5, Decimal(5)))
     >>> Order(joe, cart, FidelityPromo())  # <3>
     <Order total: 42.00 due: 42.00>
     >>> Order(ann, cart, FidelityPromo())  # <4>
     <Order total: 42.00 due: 39.90>
-    >>> banana_cart = [LineItem('banana', 30, .5),  # <5>
-    ...                LineItem('apple', 10, 1.5)]
+    >>> banana_cart = (LineItem('banana', 30, Decimal('.5')),  # <5>
+    ...                LineItem('apple', 10, Decimal('1.5')))
     >>> Order(joe, banana_cart, BulkItemPromo())  # <6>
     <Order total: 30.00 due: 28.50>
-    >>> big_cart = [LineItem(str(item_code), 1, 1.0) # <7>
-    ...               for item_code in range(10)]
-    >>> Order(joe, big_cart, LargeOrderPromo())  # <8>
+    >>> long_cart = tuple(LineItem(str(sku), 1, Decimal(1)) # <7>
+    ...                  for sku in range(10))
+    >>> Order(joe, long_cart, LargeOrderPromo())  # <8>
     <Order total: 10.00 due: 9.30>
     >>> Order(joe, cart, LargeOrderPromo())
     <Order total: 42.00 due: 42.00>
@@ -29,44 +29,37 @@
 # tag::CLASSIC_STRATEGY[]
 
 from abc import ABC, abstractmethod
-import typing
-from typing import Sequence, Optional
+from collections.abc import Sequence
+from decimal import Decimal
+from typing import NamedTuple, Optional
 
 
-class Customer(typing.NamedTuple):
+class Customer(NamedTuple):
     name: str
     fidelity: int
 
 
-class LineItem:
-    def __init__(self, product: str, quantity: int, price: float):
-        self.product = product
-        self.quantity = quantity
-        self.price = price
+class LineItem(NamedTuple):
+    product: str
+    quantity: int
+    price: Decimal
 
-    def total(self):
+    def total(self) -> Decimal:
         return self.price * self.quantity
 
 
-class Order:  # the Context
-    def __init__(
-        self,
-        customer: Customer,
-        cart: Sequence[LineItem],
-        promotion: Optional['Promotion'] = None,
-    ):
-        self.customer = customer
-        self.cart = list(cart)
-        self.promotion = promotion
+class Order(NamedTuple):  # the Context
+    customer: Customer
+    cart: Sequence[LineItem]
+    promotion: Optional['Promotion'] = None
 
-    def total(self) -> float:
-        if not hasattr(self, '__total'):
-            self.__total = sum(item.total() for item in self.cart)
-        return self.__total
+    def total(self) -> Decimal:
+        totals = (item.total() for item in self.cart)
+        return sum(totals, start=Decimal(0))
 
-    def due(self) -> float:
+    def due(self) -> Decimal:
         if self.promotion is None:
-            discount = 0.0
+            discount = Decimal(0)
         else:
             discount = self.promotion.discount(self)
         return self.total() - discount
@@ -77,36 +70,37 @@ class Order:  # the Context
 
 class Promotion(ABC):  # the Strategy: an abstract base class
     @abstractmethod
-    def discount(self, order: Order) -> float:
+    def discount(self, order: Order) -> Decimal:
         """Return discount as a positive dollar amount"""
 
 
 class FidelityPromo(Promotion):  # first Concrete Strategy
     """5% discount for customers with 1000 or more fidelity points"""
 
-    def discount(self, order: Order) -> float:
-        return order.total() * 0.05 if order.customer.fidelity >= 1000 else 0
+    def discount(self, order: Order) -> Decimal:
+        rate = Decimal('0.05')
+        if order.customer.fidelity >= 1000:
+            return order.total() * rate
+        return Decimal(0)
 
 
 class BulkItemPromo(Promotion):  # second Concrete Strategy
     """10% discount for each LineItem with 20 or more units"""
 
-    def discount(self, order: Order) -> float:
-        discount = 0
+    def discount(self, order: Order) -> Decimal:
+        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
 
 
 class LargeOrderPromo(Promotion):  # third Concrete Strategy
     """7% discount for orders with 10 or more distinct items"""
 
-    def discount(self, order: Order) -> float:
+    def discount(self, order: Order) -> Decimal:
         distinct_items = {item.product for item in order.cart}
         if len(distinct_items) >= 10:
-            return order.total() * 0.07
-        return 0
-
-
+            return order.total() * Decimal('0.07')
+        return Decimal(0)
 # end::CLASSIC_STRATEGY[]