Here are some quick notes about how I got Python 2.7 running on Debian. The pointers come from the Python NW Google Group and the Debian documentation.
(1) Set up the apt/sources.list file as follows:
deb http://ftp.uk.debian.org/debian/ unstable main contrib non-free
deb http://ftp.uk.debian.org/debian/ experimental main contrib non-free
deb http://security.debian.org/ testing/updates main contrib
(2) Run aptitude and do an upgrade to refresh the package lists
(3) I had 45 packages to update so I installed them all
(4) That left me with python 2.6 installed
(5) Searched in aptitude for python 2.7. Marked it for installation
(6) Aptitude seemed to nicely manage all the dependencies.
With the above complete 'python --version' reports 2.6 and 'python2.7 --version' reports 2.7.
I'll keep the virtual box snapshot of the previous version about for a while just in case.