Improve cfg's argparse sub-parsers support

In order for sub-parsers to be useful, you need some way of knowing
which sub-parser was chosen during argument parsing. It's pretty obvious
from the current sub-parsers test case that we don't have a convenient
interface for this.

One way of doing it is to use the 'dest' argument when adding
sub-parsers:

  >>> subparsers = parser.add_subparsers(dest='cmd')
  >>> subparsers.add_parser('a')
  >>> subparsers.add_parser('b')
  >>> parser.parse_args(['a'])
  Namespace(cmd='a')

The most sensible way to map this into cfg concepts is to register
sub-parsers as an Opt. This way, we can make name and argument values
of the sub-parser as an attribute on the ConfigOpts object:

  >>> def add_parsers(subparsers):
  ...     a = subparsers.add_parser('a')
  ...     a.add_argument('id')
  ...     b = subparsers.add_parser('b')
  ...
  >>> CONF.register_cli_opt(SubCommandOpt('cmd', handler=add_parsers))
  True
  >>> CONF(['a', '10'])
  >>> CONF.cmd.name, CONF.cmd.id
  ('a', '10')

The handler method is a bit awkward, but each time cfg is to parse
command line args it takes all the registered opts and creates a new
argparse parser. So we need to be able to re-add the sub-parsers each
time.

Change-Id: I01bfd01bf8853cf57a9248b1663eb3da142366a4

0 files changed, 0 insertions, 0 deletions