import argparse

def help(args):
    args.parser.print_help()
parser = argparse.ArgumentParser(description='my program')
subparsers = parser.add_subparsers()
p_help = subparsers.add_parser('help')
p_help.set_defaults(func=help, parser=parser)
args = parser.parse_args()
args.func(args)
How to make `help` act the same as `--help` in argparse