Possible to prefer python from $PATH when building from source with CMake? (without -DPYTHON_EXECUTABLE option)

[pramodk]

Overview of the feature

When users have python module loaded where:

$ which python
/gpfs/bbp.cscs.ch/ssd/apps/bsd/2022-01-10/stage_externals/install_gcc-11.2.0-skylake/python-3.9.7-yj5alh/bin/python

Typically users do:

cmake ..   \
    -DNRN_ENABLE_CORENEURON=ON   \
    -DCORENRN_ENABLE_GPU=ON   \
    -DNRN_ENABLE_INTERVIEWS=OFF   \
    -DNRN_ENABLE_RX3D=OFF   \
    -DCMAKE_INSTALL_PREFIX=$HOME/install 

and this selects system python:

-- Python        | ON
--   EXE         | /usr/bin/python3.6
--   INC         | /usr/include/python3.6m
--   LIB         | /usr/lib64/libpython3.6m.so.1.0

Is it possible to prefer python from $PATH than system on automatically?

Foreseeable Impact

This will avoid confusion on user side.

[pramodk]

@alexsavulescu : I adding this to 8.1 milestone. If there is easy solution I think we should fix this. This is quite annoying/inconvenient behaviour. Could you take a look?

[alexsavulescu]

Sure, will have a look once done with the nbsphinx PR