sudo apt upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up update-notifier-common (3.168.5) ...
Traceback (most recent call last):
  File "/usr/lib/update-notifier/package-data-downloader", line 24, in <module>
    import debian.deb822
  File "/usr/lib/python3/dist-packages/debian/deb822.py", line 47, in <module>
    import six
ImportError: No module named 'six'
dpkg: error processing package update-notifier-common (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 update-notifier-common
E: Sub-process /usr/bin/dpkg returned an error code (1)

sudo -H pip install six
Requirement already satisfied: six in /usr/local/lib/python3.6/dist-packages

sudo -H pip2 install six
Requirement already satisfied: six in /usr/local/lib/python2.7/dist-packages