Stepython

Stepython is a browser-based Python code visualizer for students, teachers and anyone trying to understand what a piece of Python code actually does as it runs.

Paste a program and move through it with Next and Prev, one line at a time. Every variable is drawn as a shape: numbers as circles, strings as tags, lists as rows of cells, dicts as key-value tiles, sets as rings and objects as cards. Function calls appear as stacked frames, which makes recursion and nested calls easy to follow.

A practical use is tracing an algorithm, such as a word count or a recursive function, to see exactly when each value changes instead of guessing from print statements.

Python runs entirely in the browser, so no code is sent to a server. Stepython is free to use online.