You have to use open_maybe_clear_signed_file() to open clearsigned files which is available since python-apt 0.9.4. That they worked before was more an implementation accident.
** Changed in: python-apt (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to python-apt in Ubuntu. https://bugs.launchpad.net/bugs/1565767 Title: TagFile iteration raises SystemError when attempting to parse a signed .changes file Status in python-apt package in Ubuntu: Invalid Bug description: Attempting to parse a .changes file using apt_pkg.TagFile such as http://paste.ubuntu.com/15611341/ raises a SystemError. http://paste.ubuntu.com/15611387/ contains a sample Python REPL with the given file. Note that this is a change in behaviour between Trusty and Xenial, parsing the same file in Trusty (python-apt 0.9.3.5ubuntu2) has no issues. The specific unit test that failed leading to this bug report is attempting to parse the .changes file when it is signed with an unknown key. ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: python-apt 1.1.0~beta1build1 ProcVersionSignature: Ubuntu 4.4.0-16.32-generic 4.4.6 Uname: Linux 4.4.0-16-generic x86_64 ApportVersion: 2.20.1-0ubuntu1 Architecture: amd64 CurrentDesktop: Unity Date: Mon Apr 4 15:04:29 2016 InstallationDate: Installed on 2012-08-17 (1325 days ago) InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120817.1) SourcePackage: python-apt UpgradeStatus: Upgraded to xenial on 2016-03-07 (28 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/python-apt/+bug/1565767/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp