UHD custom Python install path includes `local` on Ubuntu 22.04

[jdemel]

Issue Description

If i use a custom install path, e.g. ~prefix/gnuradio, the Python install path ends up being:

~/prefix/gnuradio/local/lib/python3.10/site-packages/uhd/
~/prefix/gnuradio/local/lib/python3.10/dist-packages/usrp_mpm/

The local part should not be there.

Setup Details

I use the latest UHD-4.2 branch. I try to use a custom prefix and I'm on Ubuntu 22.04.

Expected Behavior

all Python files should end up in these folders:

~/prefix/gnuradio/lib/python3.10/site-packages/uhd/
~/prefix/gnuradio/lib/python3.10/dist-packages/usrp_mpm/

Actual Behaviour

Incorrect install path:

~/prefix/gnuradio/local/lib/python3.10/site-packages/uhd/
~/prefix/gnuradio/local/lib/python3.10/dist-packages/usrp_mpm/

Steps to reproduce the problem

git clone .....
cd uhd/host 
mkdir build
cd build
`cmake -DCMAKE_INSTALL_PREFIX=~/prefix/gnuradio ..`
make -j ...
make install

Additional Information

One place to modify would be:

https://github.com/EttusResearch/uhd/blob/dfc7b31cfb9a5a001f0786a1ad963b93aad871a6/host/python/CMakeLists.txt#L166-L173

This fixed it:

        execute_process(COMMAND ${PYTHON_EXECUTABLE} -c
            "import os,sysconfig;\
            platlib = sysconfig.get_path('platlib','posix_prefix');\
            prefix = sysconfig.get_path('data','posix_prefix');\
            print(os.path.relpath(platlib, prefix));"
            OUTPUT_VARIABLE UHD_PYTHON_DIR OUTPUT_STRIP_TRAILING_WHITESPACE
        )

[mbr0wn]

@jdemel I think we're going with your suggestion for now, although I think that there might be other install schemes viable for some other scenarios. Thanks for pointing that out!

[mbr0wn]

FYI, we're having issues making this solution work for embedded builds. Hang in there!

[jdemel]

Sounds like good news that this issue is "completed". Though, is there a commit with this change?

[mbr0wn]

There is! Same story as usual. It takes a few days for the commits to go public.

[mbr0wn]

c385d20eeea717b3859ac6a2bcc247b69fc66003