Simon Willison’s Weblog

uv: Unified Python packaging (via) Huge new release from the Astral team today. uv 0.3.0 adds a bewildering array of new features, as part of their attempt to build "Cargo, for Python".

It's going to take a while to fully absorb all of this. Some of the key new features are:

• uv tool run cowsay, aliased to uvx cowsay - a pipx alternative that runs a tool in its own dedicated virtual environment (tucked away in ~/Library/Caches/uv), installing it if it's not present. It has a neat --with option for installing extras - I tried that just now with uvx --with datasette-cluster-map datasette and it ran Datasette with the datasette-cluster-map plugin installed.
• Project management, as an alternative to tools like Poetry and PDM. uv init creates a pyproject.toml file in the current directory, uv add sqlite-utils then creates and activates a .venv virtual environment, adds the package to that pyproject.toml and adds all of its dependencies to a new uv.lock file (like this one). That uv.lock is described as a universal or cross-platform lockfile that can support locking dependencies for multiple platforms.
• Single-file script execution using uv run myscript.py, where those scripts can define their own dependencies using PEP 723 inline metadata. These dependencies are listed in a specially formatted comment and will be installed into a virtual environment before the script is executed.
• Python version management similar to pyenv. The new uv python list command lists all Python versions available on your system (including detecting various system and Homebrew installations), and uv python install 3.13 can then install a uv-managed Python using Gregory Szorc's invaluable python-build-standalone releases.

It's all accompanied by new and very thorough documentation.

The paint isn't even dry on this stuff - it's only been out for a few hours - but this feels very promising to me. The idea that you can install uv (a single Rust binary) and then start running all of these commands to manage Python installations and their dependencies is very appealing.

If you’re wondering about the relationship between this and Rye - another project that Astral adopted solving a subset of these problems - this forum thread clarifies that they intend to continue maintaining Rye but are eager for uv to work as a full replacement.