Python Tutor

Paste in Python code and step through it line by line, watching a visual diagram of variables, the call stack, and object references update in real time — the specific thing it solves is the gap between “I can read what this code does” and “I understand what’s actually happening in memory when it runs,” especially around function calls, recursion, and mutable references.

Most useful early on, when concepts like scope and reference vs. value semantics are still abstract rather than intuitive — a good companion to Automate the Boring Stuff or CS50P rather than something you’ll reach for once those clicks.