Switching from Pyenv to Uv
95 comments
·March 9, 2025quickslowdown
fluidcruft
I generally agree but one thing I find very frustrating (i.e. have not figured out yet) is how deal with extras well, particularly with pytorch. Some of my machines have GPU, some don't and things like "uv add" end up uninstalling everything and installing the opposite forcing a resync with the appropriate --extra tag. The examples in the docs do things like CPU on windows and GPU on Linux but all my boxes are linux. There has to be a way to tell it that "hey I want --extra GPU" always on this box. But I haven't figured it out yet.
para_parolu
As a person who don’t work often on python code but occasionally need to run server or tool I find UV blessing. Before that I would beg people to help me just not to figure out what combination of obscure python tools I need. Now doing “uv run server.py” usually works.
actinium226
The script thing is great. By the way those 'oddly formatted' comments at the top are not a uv thing, it's a new official Python metadata format, specifically designed to make it possible for 3rd party tools like uv to figure out and install relevant packages.
And in case it wasn't clear to readers of your comment, uv run script.py creates an ephemeral venv and runs your script in that, so you don't pollute your system env or whatever env you happen to be in.
baby_souffle
I didn't know that UV would now edit the script for you. That is just icing on the cake!
For the curious, the format is codified here: https://peps.python.org/pep-0723/
scribu
The install speed alone makes it worthwhile for me. It went from minutes to seconds.
BoorishBears
I was working on a Raspberry Pi at a hackathon, and pip install was eating several minutes at a time.
Tried uv for the first time and it was down to seconds.
midhun1234
Can confirm this is all true. I used to be the "why should I switch" guy. The productivity improvement from not context switching while pip installs a requirements file is completely worth it.
mcintyre1994
That scripting trick is awesome! One of the really nice things about Elixir and its dependency manager is that you can just write Mix.install(…) in your script and it’ll fetch those dependencies for you, with the same caching you mentioned too.
Does uv work with Jupyter notebooks too? When I used it a while ago dependencies were really annoying compared to Livebook with that Mix.install support.
y1zhou
[dead]
IshKebab
Uv really fixes Python. It takes it from "oh god I have to fight Python again" to "wow it was actually fast and easy".
I think all the other projects (pyenv, poetry, pip, etc.) should voluntarily retire for the good of Python. If everyone moved to Uv right now, Python would be in a far better place. I'm serious. (It's not going to happen though because the Python community has no taste.)
The only very minor issue I've had is once or twice the package cache invalidation hasn't worked correctly and `uv pip install` installed an outdated package until I `uv clean`ed. Not a big deal though considering it solves so many Python clusterfucks.
javchz
Agree. I mostly do front end in my day job, and despite JavaScript being a bit of a mess lang, dealing with npm is way better than juggling anaconda, miniforge, Poetry, pip, venv, etc depending on the project.
UV is such a smooth UX that it makes you wonder how something like it wasn’t part of Python from the start.
loeber
Strong agree. The respectful act of other package managers would be consider themselves deprecated and point to uv instead.
tootie
Every time people have debates over the merits of languages I always put developer environment at the top of my list. Build tools, IDE, readable stack traces. Those things boost productivity for more than concise list comprehensions or any gimmicky syntax thing. It's why Python always felt stone age to me despite have such lovely semantics.
kubav027
I am pretty happy with poetry for near future. I prefer using python interpreters installed by linux package manager. In cloud I use python docker. Poetry recently added option to install python too if I changed my mind.
I have already setup CI/CD pipelines for programs and python libraries. Using uv would probably save some time on dependency updates but it would require changing my workflow and CI/CD. I do not think it is worth the time right now.
But if you use older environments without proper lock file I would recommend switching immediately. Poetry v2 supports pyproject.toml close to format used by uv so I can switch anytime when it would look more appealing.
Another thing to consider in long term is how astral tooling would change when they will need to make money.
js2
> I prefer using python interpreters installed by linux package manager.
uv will defer to any python it finds in PATH as long as it satisfies your version requirements (if any):
https://docs.astral.sh/uv/concepts/python-versions/
It also respects any virtual environment you've already created, so you can also do something like this:
/usr/bin/python3 -m venv .venv
.venv/bin/pip install uv
.venv/bin/uv install -r requirements.txt # or
.venv/bin/uv run script ...
> Using uv would probably save some time on dependency updates but it would require changing my workflow and CI/CD.
I found it very straightforward to switch to uv. It accommodates most existing workflows.
TheIronYuppie
For scripting... HIGHLY recommend putting your dependencies inline.
E.g.:
#!/usr/bin/env python3
# /// script
# requires-python = ">=3.11"
# dependencies = [
# "psycopg2-binary",
# "pyyaml",
# ]
# ///
uv run -s file.pykylecordes
UV is such a big improvement that it moves Python from my "would use again if I had to, but would really not look forward to it" pile to my "happy to use this as needed" pile. Without disparaging the hard work by many that came before, UV shows just how much previous tools left unsolved.
zahlman
> Maybe I installed some other things for some reason lost in the sands of time.
FWIW, I was able to confirm that the listed primary dependencies account for everything in the `pip freeze` list. (Initially, `userpath` and `pyrsistent` were missing, but they appeared after pinning back the versions of other dependencies. The only project for which I couldn't get a wheel was `python-hglib`, which turned out to be pure Python with a relatively straightforward `setup.py`.)
runjake
For my use cases, uv is so frictionless it has effectively made Python tolerable for me. I primarily discovered it via Simon Willison's (@simonw) blog posts[1]. I recommend his blog highly.
vslira
I'm using exclusively uv for personal projects - and small prototypes at work - and I can't recommend it enough.
Uv makes python go from "batteries included" to "attached to a nuclear reactor"
mrbonner
Ans you can now install Python and set it to the default in your path with the --default flag. Big plus for me to replace pyenv finally.
thefreeman
finally! this was the thing keeping me from switching every time i looked into it.
bigfatfrock
I converted along with most of the people in this thread.
IMO no really hard problem is ever truly solved but as can be seen in other comments, this group of people really crushed the pain of me and *many* others, so bravo alone on that - you have truly done humanity a service.
77ko
uv is excellent! The only think I'm missing is an easy way to update all packages in an env, something like `uv update --all` or `uv update plotly`.
Which would fit in with existing uv commands[1] like `uv add plotly`.
There is an exisiting `uv lock --upgrade-package requests` but this feels a bit verbose.
[1]: https://docs.astral.sh/uv/guides/projects/#creating-a-new-pr...
eikenberry
Maybe this one will finally be adopted as the official package manager for Python? Only 20 years late, but it would be a nice development.
0cf8612b2e1e
Pfft. Pull the other one. The PSF hates the idea of dealing with something so icky.
I have been pretty pleased with uv, but I am continually worried about the funding model. What happens when the VC starts demanding a return?
__MatrixMan__
We fork it. Whatever carrot the VC's dangle can be chased by the handful who care, and the rest of us can continue using the important part.
I highly, highly recommend uv. It solves & installs dependencies incredibly fast, and the CLI is very intuitive once you've memorized a couple commands. It handles monorepos well with the "workspaces" concept, it can replace pipx with "uv tool install," handle building & publishing, and the docker image is great, you just add a FROM line to the top and copy the bin from /uv.
I've used 'em all, pip + virtualenv, conda (and all its variants), Poetry, PDM (my personal favorite before switching to uv). Uv handles everything I need in a way that makes it so I don't have to reach for other tools, or really even think about what uv is doing. It just works, and it works great.
I even use it for small scripts. You can run "uv init --script <script_name.py>" and then "uv add package1 package2 package3 --script <script_name.py>". This adds an oddly formatted comment to the top of the script and instructs uv which packages to install when you run it. The first time you run "uv run <script_name.py>," uv installs everything you need and executes the script. Subsequent executions use the cached dependencies so it starts immediately.
If you're going to ask me to pitch you on why it's better than your current preference, I'm not going to do that. Uv is very easy to install & test, I really recommend giving it a try on your next script or pet project!