Course overview

Two floors beneath Haneulseom International Airport lies a baggage center the size of a football field. The staff call it the Heap Hall. One bag can carry many tags, and a bag with no tags left on it is eventually thrown away.

That is exactly how Python's variables and objects behave. A variable is not a box that holds a value; it is a name tag hung on an object. Keep that one picture in your head, and bugs like "the list that changed the original too", "the default argument that piles up on every call" or "the sticker that showed up on every instance" stop being mysteries.

Starting today, you are the center's new tag handler. Over ten hours you will solve twelve lost-baggage cases and learn Python's object model along the way.

The people at the center

How a lesson flows

1. You receive a lost-baggage report. It says what went missing and what it takes to close the case.
2. You work through the concepts and the code with the supervisor.
3. You step through code one line at a time on the tag board. It is not an illustration: the server really runs the example and records, line by line, how the name tags and bags are connected. Along the way you first guess "what will change when the next line runs?"
4. You close the case, and the key points of the lesson are added, one line each, to the supervisor's notebook.

Each lesson closes its own case, so you can pick only the ones you need. Still, the picture from Lesson 1 comes back in every lesson, so start there.

What you need

• Enough Python to write functions and use lists, and to have built a simple class at least once.
• Python 3.14. Every example was run and checked on 3.14. Details that depend on the CPython implementation, such as the small-integer cache or sys.getsizeof values, are marked as such.
• The tag boards run right on this page. If you want to run an example yourself, save it to a .py file and run it.