As a complete aside, uv can and does do this, but for this particular optimization I'm not sure how much absolute time it ends up saving compared to pure Python in real world resolution scenarios.
uv's total memory usage isn't that much leaner than pip's, and for parsing speed it turned out that the library pip uses, packaging, was just very unoptimized at the time uv launched. This has been significantly addressed since then:
* We did a lot of work to make version parsing twice as fast: https://iscinumpy.dev/post/packaging-faster/
* Since that blog post I made typical version parse three times faster on top of that: https://github.com/pypa/packaging/pull/1082
* Also since that blog post version filtering has gone through multiple optimizations and in some cases will be more than 30x faster e.g. https://github.com/pypa/packaging/pull/1105, https://github.com/pypa/packaging/pull/1111, https://github.com/pypa/packaging/pull/1120
At this point large dependency resolves in pip are spending very little of their time doing things in packaging, like version parsing. The main non-IO time spent in large resolves is now in the core resolver, resolvelib, which I hope to one day replace with my experimental resolver nab: https://github.com/notatallshaw/nab. Nab scales to large resolves much more efficiently than resolvelib (in fact I've cross-ported some of the algorithmic efficiency gains to uv already ;o)).