As long as you don't install other versions of Python in your path, Debian's Python versions won't be affected by a new version.
If you install a different subrelease of the version of python you've got installed, you'll need to be careful to install all the modules you use for that version of python too.
Debian Python Policy
version 0.3.7.2nas@debian.org
doko@debian.org
flight@debian.org
joss@debian.org