argparse: How to specify custom help text for subparsers?

Question

Using argparse under python3, I'm trying to get subparser help text and sub-subparser help text to be set in customized ways. The following example program illustrates my issue (the example program's source code appears at the bottom of this message). This example program should be run as follows:

argtest cmd [ ... args ... ] or argtest special subcmd [ ... args ... ] where "cmd" can be "cmd00", "cmd01", etc., and "subcmd" can be "sub00", "sub01", etc.

When I run it like argtest cmd00 -h, I want to get specific help for the "cmd00" command. When I run it like argtest special sub00 -h, I want to get specific help for the "sub00" special command.

However, I am not getting these help values. Given the code below, when I run this command:

% argtest special -h

... I get this output:

usage: argtest (toplevel) special [-h] [--debug] {sub00,sub01} ...

positional arguments:
  {sub00,sub01}
    sub00        sub00 toplevel help
    sub01        sub01 toplevel help

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

However, what I want is the following:

special toplevel help

positional arguments:
  {sub00,sub01}
    sub00        sub00 toplevel help
    sub01        sub01 toplevel help

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

Likewise, when I run this:

% argtest special sub00 -h

... I get this output:

usage: argtest (toplevel) special sub00 [-h] [--debug] [--sub0 SUB0]

optional arguments:
  -h, --help   show this help message and exit
  --debug
  --sub0 SUB0  sub0-help

However, I want this:

sub00 toplevel help

optional arguments:
  -h, --help   show this help message and exit
  --debug
  --sub0 SUB0  sub0-help

It seems like the lower-level help values get ignored, and the help is always forced to use the default help for the top level, which then generates help for all of the sub-parsers.

Is there any way that I can get the help messages that I want, given that I am using subparsers nested sub-subparsers? Thank you very much.

Here is the example program:

#!/usr/bin/python3                                                                                                              

import os
import sys
import argparse

prog = None

def main():

    parser = argparse.ArgumentParser(usage=f'{prog} (toplevel)')
    parser.add_argument(
        '--verbose',
        dest='VERBOSE',
        action='store_true',
        help='verbose output'
    )

    globalopts = argparse.ArgumentParser(add_help=False)
    globalopts.add_argument(
        '--debug',
        dest='DEBUG',
        action='store_true'
    )

    command = parser.add_subparsers(
        dest='CMD',
        help=f'{prog} CMD [ ... args ... ]'
    )

    command_00 = command.add_parser('cmd00',
                                    parents=[globalopts], help='cmd00 toplevel help')
    command_00.add_argument('--a', dest='A',
                            default=None, required=0, help='cmd00-a-help')

    command_01 = command.add_parser('cmd01',
                                    parents=[globalopts], help='cmd01 toplevel help')
    command_01.add_argument('--b', dest='B',
                            default=None, required=0, help='cmd00-b-help')

    # etc. ... lots of others, up to up to command_99                                                                                                     

    special = command.add_parser('special',
                                 parents=[globalopts], add_help='special toplevel help')
    subparsers = special.add_subparsers(dest='SUBPARSERS')

    special_00 = subparsers.add_parser('sub00',
                                       parents=[globalopts], help='sub00 toplevel help')
    special_00.add_argument('--sub0', dest='SUB0',
                            default=None, required=0, help='sub0-help')

    special_01 = subparsers.add_parser('sub01',
                                        parents=[globalopts], help='sub01 toplevel help')
    special_01.add_argument('--sub1', dest='SUB1',
                            default=None, required=0, help='sub1-help')

    args, unknowns = parser.parse_known_args()

    print(f'args={vars(args)}')

    return 0

if __name__ == '__main__':
    prog = os.path.basename(sys.argv[0])
    sys.exit(main())