It's all a bit confusing, but I think if we only have python2 installed it might be a good idea to include the symlink python -> python2.7 in the package. If you install python3 (also known as python), you get the symlink of python -> python3.

When I did a basic install of Arch recently it only installed python2, but there was no symlink of python -> python2.7 included in the package. On my other computer I have Ubuntu 12.10 and I noticed they have /usr/bin/python symlinked to python2.7 as a standard, that's why hp-setup ran correctly on it the first time.

It will run fine and your printer should work. Either create that symlink or as fede says, if you already have one that points to python3, delete that symlink and create a new one pointing to python2.7, and then run hp-setup. You have to run hp-setup to get the plugin BUT hp-setup won't run properly without a /usr/bin/python symlinked to python2.7. Some of the printers require a plugin (like my LaserJet 1018), and that may be why you get the message 'filter failed'.

You need cups installed and running, and hplip installed.

Hp laser printer test page