bpo-26510: make argparse subparsers required by default (#3027)
This fixes a regression from Python 2. To get optional subparsers, use the new parameter ``add_subparsers(required=False)``. Patch by Anthony Sottile.
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@ -1539,8 +1539,8 @@ Sub-commands
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.. method:: ArgumentParser.add_subparsers([title], [description], [prog], \
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[parser_class], [action], \
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[option_string], [dest], [help], \
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[metavar])
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[option_string], [dest], [required] \
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[help], [metavar])
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Many programs split up their functionality into a number of sub-commands,
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for example, the ``svn`` program can invoke sub-commands like ``svn
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@ -1576,6 +1576,9 @@ Sub-commands
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* dest_ - name of the attribute under which sub-command name will be
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stored; by default ``None`` and no value is stored
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* required_ - Whether or not a subcommand must be provided, by default
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``True``.
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* help_ - help for sub-parser group in help output, by default ``None``
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* metavar_ - string presenting available sub-commands in help; by default it
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@ -1066,6 +1066,7 @@ class _SubParsersAction(Action):
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prog,
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parser_class,
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dest=SUPPRESS,
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required=True,
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help=None,
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metavar=None):
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@ -1079,6 +1080,7 @@ class _SubParsersAction(Action):
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dest=dest,
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nargs=PARSER,
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choices=self._name_parser_map,
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required=required,
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help=help,
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metavar=metavar)
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@ -1807,7 +1807,7 @@ class TestAddSubparsers(TestCase):
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'bar', type=float, help='bar help')
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# check that only one subparsers argument can be added
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subparsers_kwargs = {}
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subparsers_kwargs = {'required': False}
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if aliases:
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subparsers_kwargs['metavar'] = 'COMMAND'
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subparsers_kwargs['title'] = 'commands'
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@ -1907,6 +1907,41 @@ class TestAddSubparsers(TestCase):
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self.assertEqual(NS(foo=False, bar='1', baz='2'),
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parser.parse_args('1 2'.split()))
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def _test_required_subparsers(self, parser):
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# Should parse the sub command
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ret = parser.parse_args(['run'])
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self.assertEqual(ret.command, 'run')
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# Error when the command is missing
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self.assertArgumentParserError(parser.parse_args, ())
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def test_required_subparsers_via_attribute(self):
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parser = ErrorRaisingArgumentParser()
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subparsers = parser.add_subparsers(dest='command')
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subparsers.required = True
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subparsers.add_parser('run')
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self._test_required_subparsers(parser)
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def test_required_subparsers_via_kwarg(self):
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parser = ErrorRaisingArgumentParser()
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subparsers = parser.add_subparsers(dest='command', required=True)
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subparsers.add_parser('run')
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self._test_required_subparsers(parser)
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def test_required_subparsers_default(self):
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parser = ErrorRaisingArgumentParser()
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subparsers = parser.add_subparsers(dest='command')
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subparsers.add_parser('run')
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self._test_required_subparsers(parser)
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def test_optional_subparsers(self):
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parser = ErrorRaisingArgumentParser()
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subparsers = parser.add_subparsers(dest='command', required=False)
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subparsers.add_parser('run')
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# No error here
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ret = parser.parse_args(())
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self.assertIsNone(ret.command)
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def test_help(self):
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self.assertEqual(self.parser.format_usage(),
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'usage: PROG [-h] [--foo] bar {1,2,3} ...\n')
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@ -0,0 +1,3 @@
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argparse subparsers are now required by default. This matches behaviour in Python 2.
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For optional subparsers, use the new parameter ``add_subparsers(required=False)``.
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Patch by Anthony Sottile.
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