uv

uv is a Python package and project manager written in Rust, built by Astral. It's a fairly new project, only public since 2024, but it's already become a sort-of successor to Poetry.

It replaces pip, pip-tools, pipx, virtualenv, pyenv, and parts of poetry — all in one tool, and drastically faster.

How I got here

My relationship with Python dependency management has been a slow accumulation of lessons learned the hard way.

It started with small scripts written in a highschool computer class, no packaging involved at all. At university I picked Python back up for data analysis and visualization, a natural fit alongside my computational chemistry studies. That's when I first ran into environments: I learned that a .venv is crucial, because without one every package you install lands in the same global environment. Work on more than one project at a time and that becomes a real problem fast.

Next came requirements.txt, which mattered as soon as I needed to bring my environment to another machine. Then I learned why locking versions matters, the hard way: I installed an old requirements.txt, it happily pulled in the latest version of everything, and my code stopped working.

When I started at Future Facts I dove into Python more seriously and realized that locking every dependency version by hand is tedious and error-prone at any real scale. That's when I discovered Poetry and pyproject.toml, and I embraced it. Around the same time I learned to manage different Python versions with pyenv. This matters because different projects often want or require different Python versions, and juggling multiple executables and versions in your PATH by hand is tedious. pyenv makes it a non-issue. On Windows pyenv itself doesn't exist, but pyenv-win is a decent replacement.

Why I moved from Poetry to uv

This year I moved from Poetry to uv.

The first thing you notice is speed: dependency resolution and installs that took Poetry seconds to tens of seconds finish almost instantly with uv. It also manages Python versions itself, so pyenv is no longer needed either. uv python install 3.12 and a .python-version file are enough, and uv run will fetch and use the right interpreter automatically.

A few other things it does that Poetry doesn't:

• uvx runs a tool in an ephemeral, isolated environment without installing it first, similar to pipx run but built in.
• It supports inline script dependencies (PEP 723), so a single-file script can declare its own dependencies in a comment header. uv run script.py just works, no project or virtualenv setup needed.
• It ships as a single static binary, so bootstrapping it doesn't itself depend on having a working Python installation.

What I like most about it: it just works. Drop in a pyproject.toml, run uv sync, and you have a reproducible environment in seconds. No fussing with virtualenvs, no slow pip resolves. This blog itself uses uv to manage its dependencies.

I've switched to it for every Python project I touch.