export PATH=/space/freesurfer/python/linux/bin:$PATH

After setting this, any calls to python or python3 will use this install. Keep in mind that there's also a python3 link in /usr/pubsw/bin, so it's important that you /space/freesurfer/python/linux/bin comes first in your PATH.

Tensorflow GPU

If you're on a machine with cuda installed, you can use the gpu-enabled tensorflow by modifying the following search paths.

export PYTHONPATH=/space/freesurfer/python/linux/tensorflow-gpu:$PYTHONPATH
export LD_LIBRARY_PATH=/usr/local/cuda/lib64:$LD_LIBRARY_PATH