I am using emacs in python mode. 

To run a python file I use the command `C-c C-c`. 

Emacs automatically start to run python 2.7 while I would like to use python3. 

Once I have been able to solve using this method [link](https://askubuntu.com/questions/444566/how-to-use-python3-shortcuts-on-emacs) but now it is not working on ubuntu 14.04

How can I solve this?