How to fix error Xlib.error.DisplayConnectionError: Can't connect to display ":0": b'No protocol specified\n'

Temporary workaround is

$ xhost +

http://ubuntuforums.org/showthread.php?t=2290602

Ok, It was bug in python3-xlib. See https://github.com/LiuLang/python3-xlib/issues/6 for details.