I'm trying to calculate the percentage of CPU% used for a particular process using Python/Shell, but so far nothing.
I have looked at a lot of questions here, but none could help me. 
Any suggestions?
well, you can try to use the top command with "-b -n 1" and grab it's contents and than you can use cut or other tools to get what you need
NOTE: you  can add the -p option to limit to a particular process id
CPU Utilization on UNIX