import argparse
parser = argparse.ArgumentParser()
pos = parser.add_argument('pos')
print(parser.parse_known_args())

"""
without the space, --bar string is parsed as an unknown
$ python3 example.py --bar=one_two xxx
(Namespace(pos='xxx'), ['--bar=one_two'])

with the space, --bar string is parsed as a positional
$ python3 example.py --bar=one\ two xxx
(Namespace(pos='--bar=one two'), ['xxx'])

"""