Python 3.1 vs 2.6?

i just found python 3.1 in the Ubuntu Software Center today... yes i know, i've probably been under a rock... but my question is, would installing 3.1 cause any conflicts with the 2.6 installation in terms of retro compatibility with python based apps?

i don't know if 3.1 is supposed to replace the older version or run side-by-side because of major changes or what-not.

could someone give me a briefing?