Probably better than editing /etc/apache2/sites-available/default is global activation for mod_python. It should work independently where you store yours sites.

So if you decide that e.g. you want your user to put sites in /home/user_login/public_html you just need to activate userdir mode. They will can use python in scripts automaticaly

In /etc/apache2/mods-available/ create file mod_python.conf with this content (if you want Publisher Handler):

<IfModule mod_python.c>
  AddHandler mod_python .py
  PythonHandler mod_python.publisher
  PythonDebug On
</IfModule>

or this (if you want PSP Handler):

<IfModule mod_python.c>
  AddHandler mod_python .psp
  PythonHandler mod_python.psp
  PythonDebug On
</IfModule>

Then you need to activate mod_python by: a2enmo mod_python. If it was already activated, deactivate it with a2dismod first or create symlink in /etc/apache2/mods-enabled/ to mod_python.conf by hand.