Issue 38438: argparse "usage" overly-complex with nargs="*"

This program:

import argparse
ap = argparse.ArgumentParser()
ap.add_argument("arg", nargs="*")
ap.parse_args()

Gives usage message:
usage: help_complexity.py [-h] [arg [arg ...]]

It's correct, but unnecessarily complex and challenging to the user.
If I were manually writing the usage, arg... would do, or maybe [arg ...] to be consistent with other messages??

I think [arg ...] would make sense.

Removing 3.5 and 3.6, since they're in security only mode. Adding 3.9.

Bob, would like to create a PR?

I’m happy to write one. This seems like a pretty straightforward fix.

Bob, as OP you get first dibs on a PR.
Brandt, you're next in line :-)

The `[arg [arg ...]]` feels a bit more formal to me, and I might prefer it in the example shown where the arg name is fairly short. That said, `man mv` shows something like:

    mv [OPTION]... [-T] SOURCE DEST
    mv [OPTION]... SOURCE... DIRECTORY
    mv [OPTION]... -t DIRECTORY SOURCE...

For backward compatibility with 2 metavars, the two-name form should still be possible. Just pass metavar=("FOO", "FOO").

I don't think it's any more precise. It just seems verbose and confusing to me, while conveying the same information.

`[arg [arg ...]]` to me means "optionally, an arg followed by one or more optional args".

While `[arg ...]` to  me means "optionally, one or more args".

So, I'd vote for the simpler version, especially since we're presumably trying to communicate with people who aren't BNF or regex experts!

I went ahead and opened a PR, since it's been a month.

New changeset a0ed99bca8475cbc82e9202aa354faba2a4620f4 by Raymond Hettinger (Brandt Bucher) in branch 'master':
bpo-38438: Simplify argparse "star nargs" usage. (GH-17106)
https://github.com/python/cpython/commit/a0ed99bca8475cbc82e9202aa354faba2a4620f4

Bob, thanks for the suggestion.

Brandt, thanks for the PR.

resolution: fixed
stage: patch review -> resolved

messages: + msg354410
versions: + Python 3.9, - Python 3.5, Python 3.6