see if we can support modifying the PYTHONPATH env var from cmake.

[cyrush]

two use cases:

1. if they can set additional python paths in a host-config this could help folks configure python packages (eg: numpy) without env vars & we could do this per platform in an centralized way.

2. if we can figure out the best way to support PYTHONPATH env var for custom commands, this could also help us avoid the python module warning "you are installing your module to a place that isn't in your sys.path()" that shows up when we build the conduit python module

[cyrush]

in future versions of cmake we may be able to use cmake -E env

add_custom_command(OUTPUT  ${CMAKE_CURRENT_BINARY_DIR}/build
        COMMAND ${CMAKE_COMMAND} -E env PYTHONPATH=${CMAKE_BINARY_DIR}/${dest_dir} 
        ${PYTHON_EXECUTABLE} ${setup_file} -v
        build
        --build-base=${CMAKE_CURRENT_BINARY_DIR}/build
        install
        --install-purelib=${CMAKE_BINARY_DIR}/${dest_dir}
        DEPENDS  ${setup_file} ${ARGN}
        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})

[cyrush]

Will setting CMake Python Module dir help?

[cyrush]

on linux and osx, we can use shell syntax to set the python path env var,

for example instead of
${PYTHON_EXECUTABLE} ${setup_file} -v

use:
PYTHONPATH=${CMAKE_BINARY_DIR}/${dest_dir} ${PYTHON_EXECUTABLE} ${setup_file} -v

it's not clear if this helps us on windows

[cyrush]

closing this, it's a build time message -- and has never lead to a real issue.

We expect to build in our own location, we can recast this as just a friendly reminder we are doing so.