current release version 1.1 does not have the latest changes for python3 support, so when installing it with pip3 get the code that is not supported on pyhton3.
pip3 --no-cache-dir install pynetlinux
Collecting pynetlinux
Downloading https://files.pythonhosted.org/packages/b4/4c/c6e68c8e0020824c1361faab29abd7801234948f61f988ed6c18dc30586c/pynetlinux-1.1.tar.gz
Building wheels for collected packages: pynetlinux