This is not getting much attention for several reasons:

- there's quite a backlog of argparse patches and issues

- 'set_defaults' is not commonly used.  Setting default in 'add_argument' seems more common.

- defining the same argument for both the parser and subparser can create other difficulties.

- in Bethard's example, 'set_default' sets an attribute that has no connection to any argument.  It's a cleaver trick that few users will think to use, and probably won't be of much value.

The idea proposed here of using a subnamespace for the subparser is interesting.  It reminds me of a StackOverflow question about implementing nested namespaces.

http://stackoverflow.com/questions/18668227