[Bug 1924604] Re: do-release-upgrade crashed with KeyError in __getitem__(): "The cache has no package named 'python-is-python2'"

[Timo Aaltonen]

Hello Brian, or anyone else affected,

Accepted ubuntu-release-upgrader into focal-proposed. The package will
build now and be available at https://launchpad.net/ubuntu/+source
/ubuntu-release-upgrader/1:20.04.34 in a few hours, and then in the
-proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
focal to verification-done-focal. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-focal. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: ubuntu-release-upgrader (Ubuntu Focal)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-focal

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https://bugs.launchpad.net/bugs/1924604

Title:
  do-release-upgrade crashed with KeyError in __getitem__(): "The cache
  has no package named 'python-is-python2'"

Status in ubuntu-release-upgrader package in Ubuntu:
  Fix Released
Status in ubuntu-release-upgrader source package in Focal:
  Fix Committed

Bug description:
  [Impact]
  Users with universe not enabled and python2 packages installed are unable to upgrade from Ubuntu 18.04 to Ubuntu 20.04.

  [Test Plan]
  -----------
  On an Ubuntu 18.04 system with universe and multiverse disabled
  1) apt-get install duplicity (it depends on python2.7)
  2) run do-release-upgrade

  Observe the upgrader hang at Calculating the changes (in text mode)
  kill it and observe a Traceback in /var/log/dist-upgrade/main.log.

  ...
    File "/usr/lib/python3/dist-packages/apt/cache.py", line 303, in __getitem__
      raise KeyError('The cache has no package named %r' % key)
  KeyError: "The cache has no package named 'python-is-python2'"

  With the version of the release-upgrader from -proposed (do-release-
  upgrade -p) you'll instead receive a message regarding universe not
  being enabled and the need to either remove python2 packages or enable
  universe.

  [Where problems could occur]
  The switch to using the finally clause in DistUpgradeCache.py is a significant (albeit safe) change but it is necessary for the error message to actually be displayed. So it'd make sense to run through a whole release upgrade to ensure that the gui behaves normally.

  [Original Description]
  This is because python-minimal was installed and universe was not enabled on the system being upgraded.

  Error Tracker buckets:
  https://errors.ubuntu.com/problem/f92900f3c057db7600d88857e7c05434b69d2496
  https://errors.ubuntu.com/problem/23e6edb38993cb74331d30beeadccdfffe1d557a

  ProblemType: CrashDistroRelease: Ubuntu 20.04
  Package: ubuntu-release-upgrader-core 1:20.04.31
  ProcVersionSignature: Ubuntu 5.4.0-71.79~18.04.1-generic 5.4.101
  Uname: Linux 5.4.0-71-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.23
  Architecture: amd64
  CrashDB: ubuntu
  Date: Thu Apr 15 10:59:53 2021
  ExecutablePath: /usr/bin/do-release-upgrade
  ExecutableTimestamp: 1606763386
  InstallationDate: Installed on 2021-04-13 (1 days ago)
  InstallationMedia: Ubuntu 18.04.5 LTS "Bionic Beaver" - Release amd64 (20200806.1)
  InterpreterPath: /usr/bin/python3.6
  PackageArchitecture: all
  ProcCmdline: /usr/bin/python3 -s ./focal --frontend DistUpgradeViewText
  ProcCwd: /tmp/ubuntu-release-upgrader-e397n4sn
  ProcEnviron:
   TERM=screen
   SHELL=/bin/bash
   LANG=en_US.UTF-8
   LC_CTYPE=en_US.UTF-8
   PATH=(custom, no user)
  Python3Details: /usr/bin/python3.6, Python 3.6.9, python3-minimal, 3.6.7-1~18.04
  PythonArgs: ['/usr/bin/do-release-upgrade', '--frontend', 'DistUpgradeViewText']
  PythonDetails: /usr/bin/python2.7, Python 2.7.17, python-minimal, 2.7.15~rc1-1SourcePackage: ubuntu-release-upgrader
  Title: do-release-upgrade crashed with KeyError in __getitem__(): "The cache has no package named 'python-is-python2'"
  UpgradeStatus: Upgraded to bionic on 2021-04-15 (0 days ago)

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