According to calibre debug the ipconfig command returned some invalid utf-8 characters (I think is maybe an issue due to the Python2 switch-off as the 4.x version worked fine).
To solve this I've changed the external call and modified the regex to match both the output of "ipconfig" and that of "wmic".
THIS IS ON THE MASTER BRANCH. The Master branch will be Python 3.0 from now on. While Python 2.7 support will not be deliberately broken, all efforts should now focus on Python 3.0 compatibility.
I can see a lot of work has been done. There's more to do. I've bumped the version number of everything I came across to the next major number for Python 3.0 compatibility indication.
Thanks everyone. I hope to update here at least once a week until we have a stable 7.0 release for calibre 5.0
Derek Tracy