Which is better to use in a python automation script for following simple operations
To create a zip file and copy it or rename it to a new location.
Using python inbuilt functions or terminal commands through os.system modules is better?
Using python internals command is nice, especially in terms of portability. 
But at some point, you can be confused by lack of "os.kill" in Python older than 2.7 (Windows), you can be surprised by way how os.Popen is working, than you will discover win32pipe etc etc.
Personally I would suggest always a small research (do you need daemons etc) and then decide. If you don't need windows platform - using python's internals could be more efficient.
Which is better? Using inbuilt python functions or os.system commands?