python - argparse subcommands with nested namespaces

Question

Does argparse provide built-in facilities for having it parse groups or parsers into their own namespaces? I feel like I must be missing an option somewhere.

Edit: This example is probably not exactly what I should be doing to structure the parser to meet my goal, but it was what I worked out so far. My specific goal is to be able to give subparsers groups of options that are parsed into namespace fields. The idea I had with parent was simply to use common options for this same purpose.

Example:

import argparse

# Main parser
main_parser = argparse.ArgumentParser()
main_parser.add_argument("-common")

# filter parser
filter_parser = argparse.ArgumentParser(add_help=False)
filter_parser.add_argument("-filter1")
filter_parser.add_argument("-filter2")

# sub commands
subparsers = main_parser.add_subparsers(help='sub-command help')

parser_a = subparsers.add_parser('command_a', help="command_a help", parents=[filter_parser])
parser_a.add_argument("-foo")
parser_a.add_argument("-bar")

parser_b = subparsers.add_parser('command_b', help="command_b help", parents=[filter_parser])
parser_b.add_argument("-biz")
parser_b.add_argument("-baz")

# parse
namespace = main_parser.parse_args()
print namespace

This is what I get, obviously:

$ python test.py command_a -foo bar -filter1 val
Namespace(bar=None, common=None, filter1='val', filter2=None, foo='bar')

But this is what I am really after:

Namespace(bar=None, common=None, foo='bar', 
          filter=Namespace(filter1='val', filter2=None))

And then even more groups of options already parsed into namespaces:

Namespace(common=None, 
          foo='bar', bar=None,  
          filter=Namespace(filter1='val', filter2=None),
          anotherGroup=Namespace(bazers='val'),
          anotherGroup2=Namespace(fooers='val'),
          )

I've found a related question here but it involves some custom parsing and seems to only covers a really specific circumstance.

Is there an option somewhere to tell argparse to parse certain groups into namespaced fields?

Answer 1

If the focus is on just putting selected arguments in their own namespace, and the use of subparsers (and parents) is incidental to the issue, this custom action might do the trick.

class GroupedAction(argparse.Action):    
    def __call__(self, parser, namespace, values, option_string=None):
        group,dest = self.dest.split('.',2)
        groupspace = getattr(namespace, group, argparse.Namespace())
        setattr(groupspace, dest, values)
        setattr(namespace, group, groupspace)

There are various ways of specifying the group name. It could be passed as an argument when defining the Action. It could be added as parameter. Here I chose to parse it from the dest (so namespace.filter.filter1 can get the value of filter.filter1.

# Main parser
main_parser = argparse.ArgumentParser()
main_parser.add_argument("-common")

filter_parser = argparse.ArgumentParser(add_help=False)
filter_parser.add_argument("--filter1", action=GroupedAction, dest='filter.filter1', default=argparse.SUPPRESS)
filter_parser.add_argument("--filter2", action=GroupedAction, dest='filter.filter2', default=argparse.SUPPRESS)

subparsers = main_parser.add_subparsers(help='sub-command help')

parser_a = subparsers.add_parser('command_a', help="command_a help", parents=[filter_parser])
parser_a.add_argument("--foo")
parser_a.add_argument("--bar")
parser_a.add_argument("--bazers", action=GroupedAction, dest='anotherGroup.bazers', default=argparse.SUPPRESS)
...
namespace = main_parser.parse_args()
print namespace

I had to add default=argparse.SUPPRESS so a bazers=None entry does not appear in the main namespace.

Result:

>>> python PROG command_a --foo bar --filter1 val --bazers val
Namespace(anotherGroup=Namespace(bazers='val'), 
    bar=None, common=None, 
    filter=Namespace(filter1='val'), 
    foo='bar')

If you need default entries in the nested namespaces, you could define the namespace before hand:

filter_namespace = argparse.Namespace(filter1=None, filter2=None)
namespace = argparse.Namespace(filter=filter_namespace)
namespace = main_parser.parse_args(namespace=namespace)

result as before, except for:

filter=Namespace(filter1='val', filter2=None)