[Bug 1046438] [NEW] Stack trace when package has no candidate in debug mode

[Marc Tardif]

Public bug reported:

This is what I get when running unattended-upgrades --debug:

Initial blacklisted packages:
Starting unattended upgrades script
...
Traceback (most recent call last):
  File "/usr/bin/unattended-upgrades", line 491, in <module>
    main()
  File "/usr/bin/unattended-upgrades", line 292, in main
    logging.debug("Checking: %s (%s)" % (pkg.name, map(str,
pkg.candidate.origins)))
AttributeError: 'NoneType' object has no attribute 'origins'

The problem is that the unattended-upgrades script doesn't check the
value of pkg.candidate before calling the origins attribute on it. As
can be seen in the apt.package.Package class, the candidate attribute
might be None:

    def candidate(self):
        """Return the candidate version of the package.

        This property is writeable to allow you to set the candidate version
        of the package. Just assign a Version() object, and it will be set as
        the candidate version.
        """
        cand = self._pcache._depcache.get_candidate_ver(self._pkg)
        if cand is not None:
            return Version(self, cand)

Therefore, the unattended-upgrades script should expect this eventually.
This can easily be done by using getattr and returning an empty list
there are no candidates.

** Affects: unattended-upgrades (Ubuntu)
     Importance: Undecided
         Status: New

** Branch linked: lp:~cr3/ubuntu/quantal/unattended-upgrades/1046438

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https://bugs.launchpad.net/bugs/1046438

Title:
  Stack trace when package has no candidate in debug mode

Status in “unattended-upgrades” package in Ubuntu:
  New

Bug description:
  This is what I get when running unattended-upgrades --debug:

  Initial blacklisted packages:
  Starting unattended upgrades script
  ...
  Traceback (most recent call last):
    File "/usr/bin/unattended-upgrades", line 491, in <module>
      main()
    File "/usr/bin/unattended-upgrades", line 292, in main
      logging.debug("Checking: %s (%s)" % (pkg.name, map(str,
  pkg.candidate.origins)))
  AttributeError: 'NoneType' object has no attribute 'origins'

  The problem is that the unattended-upgrades script doesn't check the
  value of pkg.candidate before calling the origins attribute on it. As
  can be seen in the apt.package.Package class, the candidate attribute
  might be None:

      def candidate(self):
          """Return the candidate version of the package.

          This property is writeable to allow you to set the candidate version
          of the package. Just assign a Version() object, and it will be set as
          the candidate version.
          """
          cand = self._pcache._depcache.get_candidate_ver(self._pkg)
          if cand is not None:
              return Version(self, cand)

  Therefore, the unattended-upgrades script should expect this
  eventually. This can easily be done by using getattr and returning an
  empty list there are no candidates.

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