import argparse

parser = argparse.ArgumentParser()
parser.add_argument('-k', '--known', action='store_true')

args, unknown = parser.parse_known_args('-u -k'.split())
assert args.known
assert len(unknown) == 1

args, unknown = parser.parse_known_args('-u unknown -k'.split())
assert args.known
assert len(unknown) == 2

# Good so far, but the asserts below fail
args, unknown = parser.parse_known_args('-uk'.split())
assert args.known
assert len(unknown) == 1

args, unknown = parser.parse_known_args('-ku'.split())
assert args.known
assert len(unknown) == 1