Figuring out library holes in the package installation process

[Brett Cannon]

With the big push we are all working towards standards, I thought it would be interesting to outline the steps it takes to go from requesting a package to be installed to it ending up on disk (see my first email on such an outline). After getting feedback on that outline, I then decided to try and pair each complicated step of that outline with the PEP and a library that essentially implements that step. I'm doing this to see where there might be a missing PEP and where that are missing library implementations of a specific PEP.

I've ended up with some holes on both the PEP and library side, so I'm hoping that either I'm overlooking something or that I've at least identified a place where some help might be appreciated by people.

1. Specify package requirement (PEP 508/packaging)
1. Translate name to PyPI-compatible name
2. Tease out requirement details (e.g. version, markers, etc.)
2. Check if package is already installed (PEP 376/XXX)
3. Check wheel cache (XXX/XXX)
4. Check PyPI for package
5. Choose appropriate file
1. Get list of files (PEP 503/_)
2. Calculate best-fitting wheel (PEPs 425 & 427/XXX)
3. Fallback to .tar.gz sdist if necessary & available
6. Download file
7. If sdist:
1. Extract
2. Read pyproject.toml (PEP 518/XXX)
3. Create venv
4. Install build dependencies
1. Static (PEP 518/_)
2. Dynamic (PEP 517/XXX)
5. Build wheel (PEP 517/XXX)
8. Cache wheel (XXX/XXX)
9. Get dependency requirements of the wheel (PEP 566/XXX)
10. Check if dependencies are already installed (like step 2)
    
11. Install missing dependencies (like step 12 below)
    
12. Install wheel (PEP 427/XXX)
1. To appropriate location (e.g. user, venv, etc.)
2. Library, scripts, etc. to appropriate locations
13. Record the installation (PEP 427/XXX)

[Brett Cannon]

Based on no one speaking up, I'm assuming I wasn't wrong with my outline. ;) That looks like there may be one PEP to write and a few things to add to 'packaging' (or other projects as appropriate).