I am running Ubuntu 16.04 and on my server I have 2 version of python , python3.5 and python3.6.
What I already tried is:
uninstalling python3-apt
and reinstalling it, didn't help still the same error.
EDIT: on python3
I have python3.6 running.
Added error:
Traceback (most recent call last):
File "/usr/bin/add-apt-repository", line 11, in <module>
from softwareproperties.SoftwareProperties import SoftwareProperties, shortcut_handler
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 27, in <module>
import apt_pkg
sudo apt install python-apt