What command should be use when the testing of arguments is failed?

[Peng Yu]

I have the following python code snippet. I'm wondering what command I
should use to terminate the program if the arguments are not right.

#!/usr/bin/env python

import sys
import os

if len(sys.argv) <= 1:
print "usage:", os.path.basename(sys.argv[0]), '<something>'
return ## what command should be used here to terminate the program?