Lesson 1: Classes, your own kinds of object

Module 9 · Lesson 1 · About 50 minutes · Needs: Module 6 (functions, parameters), Module 7 (imports, the booknook package, date), Module 3 f-strings

The situation

Amira wants lending and returning done properly. "When Jonah's Frankenstein is out, I want the program to know it is out, know it is his, and know what he owes, without you looking anything up."

Right now a loan is a dictionary, and its rules are loose functions in booknook/dates.py and booknook/fees.py. This lesson builds your own kinds of value, Book, Member and Loan, that carry their data and rules together. Jonah's loan L04, Frankenstein, borrowed Monday 14 September 2026, 16 days late today and capped at 300 pence, runs through the lesson.