Learn Web Development with Python

Inheritance and composition

But this is just half of the story, OOP is much more powerful. We have two main design constructs to exploit: inheritance and composition.

Inheritance means that two objects are related by means of an Is-A type of relationship. On the other hand, composition means that two objects are related by means of a Has-A type of relationship. It's all very easy to explain with an example:

# oop/class_inheritance.pyclass Engine:    def start(self):        pass    def stop(self):        passclass ElectricEngine(Engine):  # Is-A Engine    passclass V8Engine(Engine):  # Is-A Engine    passclass 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, ...