Release upgrade does not function in chroot - missing python apt module

[Schaap]

Trying to upgrade an ubuntu 13.04 x86 chroot on a kubuntu 13.10 x64 host (recently upgraded from 13.04) using do-release-upgrade. Installed do-release-upgrade by running
apt-get install ubuntu-release-upgrader-core
which installs the binaries. Running do-release-upgrade after that fails with the message that python can't find its apt module. ubuntu-release-upgrader-core should probably depend on python-apt. I installed both python-apt and python3-apt, not sure which is actualy needed. After this do-release-upgrade runs better.

To be complete: I had to mount some system directories into my chroot, which I did as usual by running on the host:
sudo mount -t proc none ~/chroot/proc/
sudo mount -t sysfs none ~/chroot/sys/
sudo mount -B /dev ~/chroot/dev/
One or more of these is needed for the upgrade script to work. This left only some unicode-related crashes in the upgrade scripts which I fixed by just commenting out the lines where they occurred - no time to dig further into that, I'm afraid.