bpo-33109: argparse subparsers are once again not required by default… · pythoncapi/cpython@8ebf5ce · GitHub
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bpo-33109: argparse subparsers are once again not required by default (pythonGH-6919)
bpo-26510 in 3.7.0a2 changed the behavior of argparse to make subparsers required by default, returning to the behavior of 2.7 and 3.2. The behavior was changed in 3.3 to be no longer required. While it might make more sense to have the default to required, compatibility with 3.3 through 3.6 is probably less disruptive than trying to reintroduce compatibility with 2.7 at this point. This change restores the 3.6 behavior.
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‎Doc/library/argparse.rst‎

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‎Lib/argparse.py‎

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@@ -1077,7 +1077,7 @@ def __init__(self,
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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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required=False,
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help=None,
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metavar=None):
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‎Lib/test/test_argparse.py‎

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@@ -1932,7 +1932,9 @@ 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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# 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_optional_subparsers(self):
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parser = ErrorRaisingArgumentParser()

‎Misc/NEWS.d/3.7.0a2.rst‎

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@@ -477,6 +477,8 @@ module now requires sqlite version at least 3.3.9.
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argparse subparsers are now required by default. This matches behaviour in
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Python 2. For optional subparsers, use the new parameter
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``add_subparsers(required=False)``. Patch by Anthony Sottile.
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(As of 3.7.0rc1, the default was changed to not required as had been the case
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since Python 3.3.)
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‎Misc/NEWS.d/next/Library/2018-05-16-14-57-58.bpo-33109.nPLL_S.rst‎

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