Debian Etch comes with Python version 2.4. You can easily install Python 2.5 with the command
sudo aptitude install python2.5
But even after installation, when you type python at the command prompt or run CGI scripts, you will be faced with Python 2.4.
That’s because python is just a symbolic link to /usr/bin/python2.4. To make Python 2.5 the default, you need to change the symbolic link to point to your newer version of Python. Try this:
ln -sf /usr/bin/python2.5 /usr/bin/python
Here, ln is the linking command, s makes the link symbolic, f forces the link to be overwritten, /usr/bin/python2.5 is the target and /usr/bin/python is the link name.
Voila!