Python argparse: Make at least one argument required

I've been using argparse for a Python program that can -process, -upload or both:

parser = argparse.ArgumentParser(description='Log archiver arguments.')parser.add_argument('-process', action='store_true')parser.add_argument('-upload',  action='store_true')args = parser.parse_args()

The program is meaningless without at least one parameter. How can I configure argparse to force at least one parameter to be chosen?

UPDATE:

Following the comments: What's the Pythonic way to parametrize a program with at least one option?