How to make argparse parsers also function as subparsers

Question

Say I have some parsers already defined:

foo_parser = argparse.ArgumentParser()
foo_parser.add_argument('-f')

bar_parser = argparse.ArgumentParser()
bar_parser.add_argument('-b')

Now I want those parsers to appears as sub-parsers.

parser = argparse.ArgumentParser(prog='parent')
subparsers = parser.add_subparsers()

subparsers.add_parser('foo')   # how can I associate these subparsers 
subparsers.add_parser('bar')   # with my foo and bar parsers already defined?

I know I could do this by repeating all of the add_argument calls, but I'm hoping for a DRY solution.

Does argparse allow this, or do I have to define my subparsers anew?

The reason I am asking, is that I have a collection of stand-alone scripts that I don't want to monkey with, but I would also like to provide a unified interface via sub-commands. I want to import the parsers from each of the standalone scripts, and make them behave as subparsers in the unified interface.

Answer 1

Have you tried the parents mechanism? It's a way of populating a new parser (including a subparser) with arguments (and groups) from another parser. Some even use it as a way of adding a subset of arguments to multiple subparsers. It copies the arguments (Action objects) by reference. Usually that works ok, but it imposes limits on customizing the arguments.

https://docs.python.org/3/library/argparse.html#parents

==================

A subparser is created with this method:

class _SubParsersAction(Action):
    def add_parser(self, name, **kwargs):
       ....
       parser = self._parser_class(**kwargs)
       ....
       return parser

In theory it could be customized to work with your predefined parser instead of creating a new one. It probably would take me a half hour to debug such a change.