> > I just saw this message and hurried myself up to test the patch to
> > python-build-system that I made. Unfortunately, it turns out the
> > "PYTHONNOUSERSITE=1" env var breaks pip which tries to install wheels to
> > the system site directory and fails due to a read-only filesystem.  
> 
> I'm not sure I follow; why would PYTHONNOUSERSITE affect pip?  I thought
> it should only appear in wrappers of Python executables, not be set in a
> profile's environment (thus not affecting pip) ?

Indeed. And once I make my change, PYTHONNOUSERSITE gets also placed in
the wrapper of the `pip` executable.

> Could you share the diff of the patch you tried so far?

I am attaching the patch file.

I was trying to test with

    ./pre-inst-env guix shell -C --network --no-cwd python-xmldiff coreutils python-pip
    pip install xmldiff==2.4
    echo > ~/.local/lib/python3.10/site-packages/xmldiff/main.py
    xmldiff --help

Without my patch, we get an error on 4th line. With my patch, we get
the "Read-only file system" error on the 2nd line

Best,
Wojtek

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