Running two python versions in 12.04

[Jim Byrnes]

I would like to add Python 3.3 to my 12.04 installation.  I am thinking 
of using the  deadsnakes PPA to do the installation.  If i do that am I 
correct in thinking:

There will be no conflicts - the system will still use Python 2.7.3?

To run a Python 2 program I would type python program_name.py or put 
just python in the shebang line?

To run a Python 3 program I would type python3 program_name.py or put 
python3 in the shebang line?

It would be great if someone who has done this can tell me if I am 
correct or not.

Thanks,  Jim