ch15: draft examples

15-more-types/cafeteria/cafeteria.py

@@ -0,0 +1,41 @@
+from typing import TypeVar, Generic
+
+
+class Beverage:
+    """Any beverage"""
+
+
+class Juice(Beverage):
+    """Any fruit juice"""
+
+
+class OrangeJuice(Juice):
+    """Delicious juice Brazilian oranges"""
+
+
+class Coak(Beverage):
+    """Secret formula with lots of sugar"""
+
+
+BeverageT = TypeVar('BeverageT', bound=Beverage)
+JuiceT = TypeVar('JuiceT', bound=Juice)
+
+
+class BeverageDispenser(Generic[BeverageT]):
+
+    beverage: BeverageT
+
+    def __init__(self, beverage: BeverageT) -> None:
+        self.beverage = beverage
+
+    def dispense(self) -> BeverageT:
+        return self.beverage
+
+
+class JuiceDispenser(BeverageDispenser[JuiceT]):
+    pass
+
+
+class Cafeteria:
+    def __init__(self, dispenser: BeverageDispenser[JuiceT]):
+        self.dispenser = dispenser

15-more-types/cafeteria/cafeteria_demo.py

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+from cafeteria import (
+    Cafeteria,
+    BeverageDispenser,
+    JuiceDispenser,
+    Juice,
+    OrangeJuice,
+    Coak,
+)
+
+orange = OrangeJuice()
+
+orange_dispenser: JuiceDispenser[OrangeJuice] = JuiceDispenser(orange)
+
+juice: Juice = orange_dispenser.dispense()
+
+soda = Coak()
+
+## Value of type variable "JuiceT" of "JuiceDispenser" cannot be "Coak"
+# soda_dispenser = JuiceDispenser(soda)
+
+soda_dispenser = BeverageDispenser(soda)
+
+arnold_hall = Cafeteria(soda_dispenser)