by zahlman | 2025-12-27 05:24:33+00:00
> it's how much speed we "unlocked" just by finally treating Python packaging as a well-specified systems problem instead of a pile of historical accidents.

A lot of that, in turn, boils down to realizing that it could be fast, and then expecting that and caring enough about it.

> but with the same design decisions (PEP 517/518/621/658 focus, HTTP range tricks, aggressive wheel-first strategy, ignoring obviously defensive upper bounds, etc.), I strongly suspect we'd be debating a 1.3× vs 1.5× speedup instead of a 10× headline

I'm doing a project of this sort (although I'm hoping not to reinvent the wheel (heh) for the actual resolution algorithm). I fully expect that some things will be barely improved or even slower, but many things will be nearly as fast as with uv.

For example, installing from cache (the focus for the first round) mainly relies on tools in the standard library that are written in C and have to make system calls and interact with the filesystem; Rust can't do a whole lot to improve on that. On the other hand, a new project can improve by storing unpacked files in the cache (like uv) instead of just the artifact (I'm storing both; pip stores the artifact, but with a msgpack header) and hard-linking them instead of copying them (so that the system calls do less I/O). It can also improve by actually making the cached data accessible without a network call (pip's cache is an HTTP cache; contacting PyPI tells it what the original download URL is for the file it downloaded, which is then hashed to determine its path).

For another example, pre-compiling bytecode can be parallelized; there's even already code in the standard library for it. Pip hasn't been taking advantage of that all this time, but to my understanding it will soon feature its own logic (like uv does) to assign files to compile to worker processes. But Rust can't really help with the actual logic being parallelized, because that, too, is written purely in C (at least for CPython), within the interpreter.

> why did it take a greenfield project to give Python the package manager behavior people clearly wanted for the last decade?

(Zeroth, pip has been doing HTTP range tricks, or at least trying, for quite a while. And the exact point of PEP 658 is to obsolete them. It just doesn't really work for sdists with the current level of metadata expressive power, as in other PEPs like 440 and 508. Which is why we have more PEPs in the pipeline trying to fix that, like 725. And discussions and summaries like https://pypackaging-native.github.io/.)

First, you have to write the standards. People in the community expect interoperability. PEP 518 exists specifically so that people could start working on alternatives to Setuptools as a build backend, and PEP 517 exists so that such alternatives could have the option of providing just the build backend functionality. (But the people making things like Poetry and Hatch had grander ideas anyway.)

But also, consider the alternative: the only other viable way would have been for pip to totally rip apart established code paths and possibly break compatibility. And, well, if you used and talked about Python at any point between 2006 and 2020, you should have the first-hand experience required to complete that thought.

Specifically regarding the "aggressive wheel-first strategy", I strongly encourage you to read the discussion on https://github.com/pypa/pip/issues/9140.