https://github.com/python/cpython/commit/a6c0c64de0ade400df7995f1e9480b6fc0f863aa commit: a6c0c64de0ade400df7995f1e9480b6fc0f863aa branch: main author: Serhiy Storchaka <[email protected]> committer: serhiy-storchaka <[email protected]> date: 2024-10-12T14:46:28+03:00 summary:
gh-59330: Improve error message for dest= for positionals (GH-125215) Also improve the documentation. Specify how dest and metavar are derived from add_argument() positional arguments. Co-authored-by: Simon Law <[email protected]> files: M Doc/library/argparse.rst M Lib/argparse.py M Lib/test/test_argparse.py diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst index d337de87ca8f39..19f832051a9ee8 100644 --- a/Doc/library/argparse.rst +++ b/Doc/library/argparse.rst @@ -636,6 +636,25 @@ be positional:: usage: PROG [-h] [-f FOO] bar PROG: error: the following arguments are required: bar +By default, argparse automatically handles the internal naming and +display names of arguments, simplifying the process without requiring +additional configuration. +As such, you do not need to specify the dest_ and metavar_ parameters. +The dest_ parameter defaults to the argument name with underscores ``_`` +replacing hyphens ``-`` . The metavar_ parameter defaults to the +upper-cased name. For example:: + + >>> parser = argparse.ArgumentParser(prog='PROG') + >>> parser.add_argument('--foo-bar') + >>> parser.parse_args(['--foo-bar', 'FOO-BAR'] + Namespace(foo_bar='FOO-BAR') + >>> parser.print_help() + usage: [-h] [--foo-bar FOO-BAR] + + optional arguments: + -h, --help show this help message and exit + --foo-bar FOO-BAR + .. _action: diff --git a/Lib/argparse.py b/Lib/argparse.py index 208c1827f9aca7..64dbd7149e769c 100644 --- a/Lib/argparse.py +++ b/Lib/argparse.py @@ -1424,7 +1424,8 @@ def add_argument(self, *args, **kwargs): chars = self.prefix_chars if not args or len(args) == 1 and args[0][0] not in chars: if args and 'dest' in kwargs: - raise ValueError('dest supplied twice for positional argument') + raise ValueError('dest supplied twice for positional argument,' + ' did you mean metavar?') kwargs = self._get_positional_kwargs(*args, **kwargs) # otherwise, we're adding an optional argument diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py index 000b810454f584..61ddb5f16cc44f 100644 --- a/Lib/test/test_argparse.py +++ b/Lib/test/test_argparse.py @@ -5411,7 +5411,8 @@ def test_multiple_dest(self): parser.add_argument(dest='foo') with self.assertRaises(ValueError) as cm: parser.add_argument('bar', dest='baz') - self.assertIn('dest supplied twice for positional argument', + self.assertIn('dest supplied twice for positional argument,' + ' did you mean metavar?', str(cm.exception)) def test_no_argument_actions(self): _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-checkins.python.org/ Member address: [email protected]
