Show defaults in --help about argparse HOT 4 CLOSED

I'm a little nervous about doing this for all help messages because sometimes 
the
Python object used as a default doesn't make sense (e.g. a function object). 
You can
use string format specifiers in the help messages though, like this::

  >>> parser = argparse.ArgumentParser()
  >>> parser.add_argument('--foo', type=int, default=123,
  ...                     help='Foo something (default: %(default)s)')
  >>> parser.print_help()
  usage: argparse.py [-h] [--foo FOO]

  optional arguments:
    -h, --help  show this help message and exit
    --foo FOO   Foo something (default: 123)

Is that enough, or are you hoping for a help formatter that automatically adds
(default: xxx) to the end of everything with a non-None default?

I, for one, would like to see such a formatter. It should probably try to check 
that
'%(default)' is not already in the string, though. I might want to override the
formatting for one argument.

Yeah, checking for '%(default)' makes a lot of sense. I'll try to add this 
feature
before the next release of argparse. It'll probably come in the form of a new
subclass of HelpFormatter.

I finally got around to this. There's now a ArgumentDefaultsHelpFormatter as of 
r28
which adds ' (default: %(default)s)' to all the help strings where the argument 
has a
default.