The argparse module incorrectly uses the terms "optional arguments" for keyword arguments.

For instance this argument parser takes a required keyword argument and an optional positional argument, but classifies the former as an "optional argument" and the latter as a "positional argument":

>>> import argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', required=True)
_StoreAction(option_strings=['--foo'], dest='foo', nargs=None, const=None, default=None, type=None, choices=None, help=None, metavar=None)
>>> parser.add_argument('bar', nargs='?')
_StoreAction(option_strings=[], dest='bar', nargs='?', const=None, default=None, type=None, choices=None, help=None, metavar=None)
>>> parser.parse_args(['-h'])
usage: [-h] --foo FOO [bar]

positional arguments:
  bar

optional arguments:
  -h, --help  show this help message and exit
  --foo FOO

Since the actual classification seems to distinguish positional from keyword arguments instead of required from optional arguments, I think that the "optional arguments:" section should be renamed to "keyword arguments:".

This related to an old issue

https://bugs.python.org/issue9694
argparse required arguments displayed under "optional arguments"

argparse defines two initial argument groups, titled 'positional arguments' and 'optional arguments'.   Alternatives have been suggested, such as 'flagged arguments' and/or 'required arguments'.  But nothing was settled.

Users can define their own argument groups. 

I'd suggest closing this a duplicate, though we can certainly revisit the earlier discussion.

Thanks paul j3 for the link. I am continuing the discussion there.