Lesson 2: Decorators: wrapping a function without changing it

Module 10 · Lesson 2 · About 45 minutes · Needs: Module 6 Lesson 3 (functions as values, nested functions, nonlocal), Module 6 Lesson 2 (*args, **kwargs), Module 7 (the booknook package)

The situation

Amira's request for this module is "Make sure it never breaks." Before anything can be tested, she wants to see what the shelf's code is doing. When a fee looks wrong, she asks: which function was called, with what, and what did it answer?

A print inside every rule would clutter it. This lesson adds the note from outside, with a decorator: a function that wraps another function and adds work around it. You will follow Ben's L13, 9 days late, which must still cost 180 pence.