BookItem is a child class of Book. So it has to call the constructor from the parent class so it can use those properties. Or am I missing something?
Also, why is Book been defined as an Abstract Class. An abstract class in python has one or more abstract methods. Book has None.
Course: Grokking the Object Oriented Design Interview - Learn Interactively
Lesson: Design a Library Management System - Grokking the Object Oriented Design Interview