Thanks for implementing #1788 , it's been great!

Since currently pyc compilation is implemented as a pass over the entire env, it can be quite costly:

λ uv pip install pypyp --compile 
Resolved 1 package in 123ms
Downloaded 1 package in 68ms
Installed 1 package in 28ms
Bytecode compiled 58064 files in 53.81s
 + pypyp==1.2.0

In this venv, it's about 1000x longer than it takes to install without pyc compilation.

Note this very slow time is on macOS, it's much better on Linux machines I have access to (more like 10s). See #2326 (comment) for my laptop specs

To be clear, this is not a particularly pressing issue. The need to bytecode compile deltas is much lower than when building things from scratch. Nevertheless, ideally uv should be significantly faster than pip in all usage scenarios.

With that in mind, some possible suggestions:

1. It looks like uv currently forces recompilation

   uv/crates/uv-installer/src/pip_compileall.py

   Line 50 in 1181aa9

   path, invalidation_mode=invalidation_mode, force=True, quiet=2

   
   I'm not sure why this is... maybe something to do with checked hash validation that compileall doesn't handle correctly? The script predates Add an option to bytecode compile during installation #2086 , so maybe there's something else going on
   (update: I've merged this change)

2. We could only bytecode compile the newly installed packages

3. If uv no longer forces recompilation, you could move the invalidation / mtime logic into Rust, not sure how much that would help, but could conceivably save you from shelling to compileall

4. Something something copy on write for pyc