kubuntu-devel-release-upgrade crashes with TypeError

Bug Description

I was upgrading from 14.04 to 14.10. After a while, I got the following exception:

  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 337, in conffile
    os.write(self.master_fd, "y\n")
TypeError: 'str' does not support the buffer interface

Here's the full output:

"""
$ kubuntu-devel-release-upgrade
Bus::open: Can not get ibus-daemon's address.
IBusInputContext::createInputContext: no connection to ibus-daemon
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [198 B]
Get:2 Upgrade tool [1,143 kB]
100% [Working] 64.5 kB/s 0sadept_manager: no process found
adept_updater: no process found
QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed: No such file or directory
QFileSystemWatcher: failed to add paths: /root/.config/ibus/bus
Bus::open: Can not get ibus-daemon's address.
IBusInputContext::createInputContext: no connection to ibus-daemon
exitMainLoop
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-opo6yaru/utopic", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeMain.py", line 239, in main
    if app.run():
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeController.py", line 1822, in run
    return self.fullUpgrade()
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeController.py", line 1787, in fullUpgrade
    if not self.doDistUpgrade():
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeController.py", line 1132, in doDistUpgrade
    res = self.cache.commit(fprogress,iprogress)
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeCache.py", line 267, in commit
    apt.Cache.commit(self, fprogress, iprogress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 501, in commit
    res = self.install_archives(pm, install_progress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 465, in install_archives
    res = install_progress.run(pm)
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeView.py", line 233, in run
    res = os.WEXITSTATUS(self.wait_child())
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 431, in wait_child
    self.update_interface()
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 410, in update_interface
    InstallProgress.update_interface(self)
  File "/usr/lib/python3/dist-packages/apt/progress/base.py", line 252, in update_interface
    self.conffile(match.group(1), match.group(2))
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 337, in conffile
    os.write(self.master_fd, "y\n")
TypeError: 'str' does not support the buffer interface
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 102, in apport_excepthook
    pr.add_proc_info(extraenv=['PYTHONPATH', 'PYTHONHOME'])
  File "/usr/lib/python3/dist-packages/apport/report.py", line 521, in add_proc_info
    raise ValueError('%s does not exist' % self['ExecutablePath'])
ValueError: /usr/bin/python3.4 (deleted) does not exist

Original exception was:
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-opo6yaru/utopic", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeMain.py", line 239, in main
    if app.run():
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeController.py", line 1822, in run
    return self.fullUpgrade()
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeController.py", line 1787, in fullUpgrade
    if not self.doDistUpgrade():
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeController.py", line 1132, in doDistUpgrade
    res = self.cache.commit(fprogress,iprogress)
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeCache.py", line 267, in commit
    apt.Cache.commit(self, fprogress, iprogress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 501, in commit
    res = self.install_archives(pm, install_progress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 465, in install_archives
    res = install_progress.run(pm)
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeView.py", line 233, in run
    res = os.WEXITSTATUS(self.wait_child())
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 431, in wait_child
    self.update_interface()
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 410, in update_interface
    InstallProgress.update_interface(self)
  File "/usr/lib/python3/dist-packages/apt/progress/base.py", line 252, in update_interface
    self.conffile(match.group(1), match.group(2))
  File "/tmp/ubuntu-release-upgrader-opo6yaru/DistUpgrade/DistUpgradeViewKDE.py", line 337, in conffile
    os.write(self.master_fd, "y\n")
TypeError: 'str' does not support the buffer interface
"""

The upgrade process doesn't exist anymore, though its window is still visible (and frozen).

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: ubuntu-release-upgrader-qt 1:14.10.7
ProcVersionSignature: Ubuntu 3.13.0-30.55-generic 3.13.11.2
Uname: Linux 3.13.0-30-generic x86_64
ApportVersion: 2.14.7-0ubuntu2
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Sun Sep 28 18:59:25 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2013-04-05 (542 days ago)
InstallationMedia: Kubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to utopic on 2014-09-29 (0 days ago)