[Moved from http://code.google.com/p/argparse/issues/detail?id=53]

It's currently not possible to have subcommands formatted in groups, e.g. instead of:

subcommands:
  {a,b,c,d,e}
    a          a subcommand help
    b          b subcommand help
    c          c subcommand help
    d          d subcommand help
    e          e subcommand help 

you should be able to get something like:

subcommands:
  group1:
    a          a subcommand help
    b          b subcommand help
    c          c subcommand help
  group2:
    d          d subcommand help
    e          e subcommand help

This patch accomplishes this task by adding a  _PseudoGroup class to _SubParsersAction.  It's like the _ChoicesPseudoAction except that it maintains its own _choices_actions list.

It takes advantage of the fact that formatter._format_actions is recursive when it comes to actions in _choices_actions.  In fact it is possible to define groups within groups (not that I would recommend that).

There is one simple test case in test_argparse, similar to the example in this issue.

This patch probably won't work with [parents].  see http://bugs.python.org/issue16807