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Comment by simonw | Hacker News Reader

I love this so much. I dug around a bit and figured out how it works - I have an explanation (with an illustrative diagram) here: https://simonwillison.net/2024/Oct/21/sudoku-in-python-packa...

Figuring out how it works is a great way to learn a bit more about how Python packaging works under the hood. I learned that .whl files contain a METADATA file listing dependency constraints as "Requires-Dist" rules.

I ran a speed comparison too. Using the uv pip resolver it took 0.24s - with the older pip-compile tool it took 17s.

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Tangent, but I wondered what libuv had to do with speeding up Python packaging, and it turns out nothing. I wonder why someone choose to name a pip replacement in a way that effectively collides with several tools and libraries across many languages...

I agree.. While I think it looks amazing, it's a poor naming choice.

Wow, uv really is fast.

As is simonw writing that post in under 60m assuming he first saw the concept here on HN.

Using the simonw resolver is took under 3600s *

Nah I wrote this one a couple of days ago when I first saw the Sudoku solving project on Mastodon.

Thank you, I was going to point out the post on your blog has date of publication lol

People keep trying to sell the speed of such solutions as a killer feature for uv, but I think I must not be anywhere near the target audience. The constraint-solving required for the sorts of projects I would typically work on is not even remotely as complex, while I'm bottlenecked by a slow, unreliable Internet connection (and the lack of a good way to tell Pip not to check PyPI for new versions and only consider what's currently in the wheel cache).

Personally I’m just a fan of people improving dev tooling, regardless of it ultimately making a huge difference to my workflow. I haven’t used uv yet, but I’m still tangentially following it because despite pip and poetry being great tools I have had my fair share of grievances with them.

Using uv (IME) should be a drop-in replacement for almost all of your python packaging needs. I highly recommend giving it a shot - it’s saved me measurable time in just a few months.

Our CI took 2 minutes to install the requirements. Adding UV dropped that to seconds. Now most time is spent on running tests, instead of installing requirements.

Of course we could've cached the venv, but cache invalidation is hard, and this is a very cheap way to avoid it.

Or you could cache the solve, surely? Simply explicitly including your transitive dependencies and pinning everything should do the trick - but there is work being done actively on a lockfile standard, it's just the sort of topic that attracts ungodly amounts of bikeshedding.

(One of these days I'll have to figure out this "CI" thing. But my main focus is really just solving interesting programming problems, and making simple elegant tools for mostly-small tasks.)

> while I'm bottlenecked by a slow, unreliable Internet connection (and the lack of a good way to tell Pip not to check PyPI for new versions and only consider what's currently in the wheel cache).

Which is one of the reasons why uv is so fast. It reduces the total times it needs to go to PyPI! Not only does it cache really well, it also hits PyPI more efficiently and highly parallel. Once you resolved once, future resolutions will likely bypass PyPI for the most part entirely.

Oh, that's good to hear. The performance discourse around uv seems to revolve around "written in Rust! Statically compiled!" all the time, but an algorithmic change like that is something that could conceivably make its way back into Pip. (Or perhaps into future competing tools still written in Python. I happen to have a design of my own.)

More significant than the speed improvement in my opinion is the space saving.

The reason uv is fast is that it creates hard links from each of your virtual environments to a single shared cached copy of the dependencies (using copy-on-write in case you want to edit them).

This means that if you have 100 projects on your machine that all use PyTorch you still only have one copy of PyTorch!

This is definitely a feature I wanted to have in my own attempt (hopefully I can start work on it before the end of the year; I think I'll bump up my mental priority for blogging about the design). I also have considered symlink (not sure if this really works) and .pth file-based approaches.

(TIL `os.link` has been supported on Windows since 3.2.)

How does it encode the idea of having all the numbers on each line/square?

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