Optional Positional Arguments with argparse

Today I helped somebody in the Python IRC channel with a question about combining required, optional and multi-value positional arguments in Python's argparse module. This is actually pretty easy to do, but not immediately obvious, so here's the example I put together. I took hints from the first example in the argparse documentation, and also this StackOverflow answer.

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('foo', default='a')
parser.add_argument('bar', default='b', nargs='?')
parser.add_argument('baz', default=[], nargs='*')
print parser.parse_args()

And does it work? Apparently so. Some example output from running this script:

$ python test.py
usage: test.py [-h] foo [bar] [baz [baz ...]]
test.py: error: too few arguments

$ python test.py x
Namespace(bar='b', baz=[], foo='x')

$ python test.py x y
Namespace(bar='y', baz=[], foo='x')

$ python test.py x y z
Namespace(bar='y', baz=['z'], foo='x')

$ python test.py x y z a
Namespace(bar='y', baz=['z', 'a'], foo='x')