Simon Willison’s Weblog

3rd December 2025

TIL: Dependency groups and uv run. I wrote up the new pattern I'm using for my various Python project repos to make them as easy to hack on with uv as possible. The trick is to use a PEP 735 dependency group called dev, declared in pyproject.toml like this:

[dependency-groups]
dev = ["pytest"]

With that in place, running uv run pytest will automatically install that development dependency into a new virtual environment and use it to run your tests.

This means you can get started hacking on one of my projects (here datasette-extract) with just these steps:

git clone https://github.com/datasette/datasette-extract
cd datasette-extract
uv run pytest

I also split my uv TILs out into a separate folder. This meant I had to setup redirects for the old paths, so I had Claude Code help build me a new plugin called datasette-redirects and then apply it to my TIL site, including updating the build script to correctly track the creation date of files that had since been renamed.