Python notebooks are a workhorse of scientific computing. But traditional notebooks have problems — they suffer from a reproducibility crisis; they are difficult to use with interactive widgets; their file format does not play well with Git; and they aren't reusable like regular Python scripts or modules.

This talk presents a marimo, an open-source reactive Python notebook that addresses these concerns by modeling notebooks as dataflow graphs and storing them as Python files. We discuss design decisions and their tradeoffs, and show how these decisions make marimo notebooks reproducible in execution and packaging, Git-friendly, executable as scripts, and shareable as apps.