This bug was fixed in the package python-apt - 1.9.0ubuntu1.4
--------------- python-apt (1.9.0ubuntu1.4) eoan; urgency=medium
* Don't duplicate disabled sources during add() (LP: #1311056)
-- Dave Jones <email address hidden> Fri, 24 Jan 2020 22:08:17 +0000
This bug was fixed in the package python-apt - 1.9.0ubuntu1.4
---------------
python-apt (1.9.0ubuntu1.4) eoan; urgency=medium
* Don't duplicate disabled sources during add() (LP: #1311056)
-- Dave Jones <email address hidden> Fri, 24 Jan 2020 22:08:17 +0000