Currently when I use \"python\" command, it points to python2.6. I have installed python3.1 and I want the \"python\" command point to python3.1. How it is possible?
You really don't want to change what python points to, because some programs might expect Python 2, and break.
python
The solution is to use virtualenv: create an isolated Python 3 environment (with the -p python3 option), activate it, and you're good to go.
-p python3