ch06

ch06/oop/class_inheritance.py

@@ -0,0 +1,57 @@
+# oop/class_inheritance.py
+class Engine:
+    def start(self):
+        pass
+
+    def stop(self):
+        pass
+
+class ElectricEngine(Engine):  # Is-A Engine
+    pass
+
+class V8Engine(Engine):  # Is-A Engine
+    pass
+
+class Car:
+    engine_cls = Engine
+
+    def __init__(self):
+        self.engine = self.engine_cls()  # Has-A Engine
+
+    def start(self):
+        print(
+            'Starting engine {0} for car {1}... Wroom, wroom!'
+            .format(
+                self.engine.__class__.__name__,
+                self.__class__.__name__)
+        )
+        self.engine.start()
+
+    def stop(self):
+        self.engine.stop()
+
+class RaceCar(Car):  # Is-A Car
+    engine_cls = V8Engine
+
+class CityCar(Car):  # Is-A Car
+    engine_cls = ElectricEngine
+
+class F1Car(RaceCar):  # Is-A RaceCar and also Is-A Car
+    pass  # engine_cls same as parent
+
+car = Car()
+racecar = RaceCar()
+citycar = CityCar()
+f1car = F1Car()
+cars = [car, racecar, citycar, f1car]
+
+for car in cars:
+    car.start()
+
+"""
+$ python class_inheritance.py
+Starting engine Engine for car Car... Wroom, wroom!
+Starting engine V8Engine for car RaceCar... Wroom, wroom!
+Starting engine ElectricEngine for car CityCar... Wroom, wroom!
+Starting engine V8Engine for car F1Car... Wroom, wroom!
+"""