Matt is asking about positional parameters in argparse, and I agree that the Python documentation is lacking on this aspect. There's not a single, complete example in the ~20 odd pages that shows both parsing and using positional parameters.
None of the other answers here show a complete example of positional parameters, either, so here's a complete example:
# tested with python 2.7.1
import argparse
parser = argparse.ArgumentParser(description="An argparse example")
parser.add_argument('action', help='The action to take (e.g. install, remove, etc.)')
parser.add_argument('foo-bar', help='Hyphens are cumbersome in positional arguments')
args = parser.parse_args()
if args.action == "install":
print("You asked for installation")
else:
print("You asked for something other than installation")
# The following do not work:
# print(args.foo-bar)
# print(args.foo_bar)
# But this works:
print(getattr(args, 'foo-bar'))
The thing that threw me off is that argparse will convert the named argument "--foo-bar" into "foo_bar", but a positional parameter named "foo-bar" stays as "foo-bar", making it less obvious how to use it in your program.
Notice the two lines near the end of my example -- neither of those will work to get the value of the foo-bar positional param. The first one is obviously wrong (it's an arithmetic expression args.foo minus bar), but the second one doesn't work either:
AttributeError: 'Namespace' object has no attribute 'foo_bar'
If you want to use the foo-bar attribute, you must use getattr, as seen in the last line of my example. What's crazy is that if you tried to use dest=foo_bar to change the property name to something that's easier to access, you'd get a really bizarre error message:
ValueError: dest supplied twice for positional argument
Here's how the example above runs:
$ python test.py
usage: test.py [-h] action foo-bar
test.py: error: too few arguments
$ python test.py -h
usage: test.py [-h] action foo-bar
An argparse example
positional arguments:
action The action to take (e.g. install, remove, etc.)
foo-bar Hyphens are cumbersome in positional arguments
optional arguments:
-h, --help show this help message and exit
$ python test.py install foo
You asked for installation
foo