how to inherit toplevel options within positional arguments in argparse

Question

I have some code which i would like to implement like git option handling.

import argparse

def get_options():
    parser = argparse.ArgumentParser(description='database maintance')
    parser.add_argument('--database', default = 'series' )

    subparsers = parser.add_subparsers(dest='operation', help='commands')
    list_parser = subparsers.add_parser('list', help='list')
    list_parser.add_argument('--tables', nargs='*', default=['all'], help="tables to list")

    repair_parser = subparsers.add_parser('repair', help='repair data')
    repair_parser.add_argument('date', help='Repair missing dates')

    delete_parser = subparsers.add_parser('delete', help='delete data')
    delete_parser.add_argument('table', nargs=1, default=argparse.SUPPRESS, help="table to delete date in")
    delete_parser.add_argument('--tables', nargs='*', default=[], help="additional tables to apply delete")

    opts = parser.parse_args()
    print(opts)
    return opts

if __name__ == '__main__':
    opts = get_options()

The problem with this code is that although you can call it this way.

$ ./maint.py list --tables t1 t2
Namespace(database='series', operation='list', tables=['t1', 't2'])

or this way..

$ ./maint.py --database main list --tables t1 t2
Namespace(database='main', operation='list', tables=['t1', 't2'])

you cannot call it this way..

$ ./maint.py list --tables t1 t2 --database main
usage: maint.py [-h] [--database DATABASE] {list,repair,delete} ...
maint.py: error: unrecognized arguments: --database main

In order to get this working I would have to add all arguments from the toplevel parser to the sub_parsers.

list_parser.add_argument('--database', default = 'series' ) 
repair_parser.add_argument('--database', default = 'series' )
delete_parser.add_argument('--database', default = 'series' )

Is there a better way to do this so that a toplevel option can be invoked by all sub_parsers ?

Answer 1

You can define the --database option in a separate parser, which is passed to both the main parser and all subparsers via the parents option.

db = argparse.ArgumentParser(add_help=False)
db.add_argument("--database", default='series')

parser = argparse.ArgumentParser(description='database maintance', parents=[db])
subparsers = parser.add_subparsers(dest='operation', help='commands')
list_parser = subparsers.add_parser('list', parents=[db], help='list')
repair_parser = subparsers.add_parser('repair', parents=[db], help='repair data')
delete_parser = subparsers.add_parser('delete', parents=[db], help='delete data')

--database can then be used either before or after a subcommand.