How to check if an argument from commandline has been set?
len(sys.argv) > 1
Don't use sys.argv for handling the command-line interface; there's a module to do that: argparse.
You can mark an argument as required by passing required=True to add_argument.
import argparse
parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument("foo", ..., required=True)
parser.parse_args()