8000 gh-85935: Check for nargs=0 for positional arguments in argparse (GH-… · python/cpython@9944ad3 · GitHub
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gh-85935: Check for nargs=0 for positional arguments in argparse (GH-124839)
Raise ValueError in add_argument() if either explicit nargs=0 or action that does not consume arguments (like 'store_const' or 'store_true') is specified for positional argument.
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-3
lines changed

3 files changed

+18
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lines changed

‎Lib/argparse.py

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1441,11 +1441,17 @@ def add_argument(self, *args, **kwargs):
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kwargs['default'] = self.argument_default
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# create the action object, and add it to the parser
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action_name = kwargs.get('action')
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action_class = self._pop_action_class(kwargs)
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if not callable(action_class):
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raise ValueError('unknown action "%s"' % (action_class,))
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action = action_class(**kwargs)
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# raise an error if action for positional argument does not
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# consume arguments
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if not action.option_strings and action.nargs == 0:
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raise ValueError(f'action {action_name!r} is not valid for positional arguments')
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# raise an error if the action type is not callable
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type_func = self._registry_get('type', action.type, action.type)
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if not callable(type_func):
@@ -1554,7 +1560,9 @@ def _get_positional_kwargs(self, dest, **kwargs):
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# mark positional arguments as required if at least one is
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# always required
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nargs = kwargs.get('nargs')
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if nargs not in [OPTIONAL, ZERO_OR_MORE, REMAINDER, SUPPRESS, 0]:
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if nargs == 0:
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raise ValueError('nargs for positionals must be != 0')
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if nargs not in [OPTIONAL, ZERO_OR_MORE, REMAINDER, SUPPRESS]:
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kwargs['required'] = True
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# return the keyword arguments with no option strings

‎Lib/test/test_argparse.py

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -5424,8 +5424,11 @@ def test_no_argument_actions(self):
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with self.subTest(attrs=attrs):
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self.assertTypeError('-x', action=action, **attrs)
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self.assertTypeError('x', action=action, **attrs)
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self.assertValueError('x', action=action,
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errmsg=f"action '{action}' is not valid for positional arguments")
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self.assertTypeError('-x', action=action, nargs=0)
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self.assertTypeError('x', action=action, nargs=0)
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self.assertValueError('x', action=action, nargs=0,
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errmsg='nargs for positionals must be != 0')
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def test_no_argument_no_const_actions(self):
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# options with zero arguments
@@ -5445,7 +5448,7 @@ def test_more_than_one_argument_actions(self):
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self.assertValueError('-x', nargs=0, action=action,
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errmsg=f'nargs for {action_name} actions must be != 0')
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self.assertValueError('spam', nargs=0, action=action,
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errmsg=f'nargs for {action_name} actions must be != 0')
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errmsg='nargs for positionals must be != 0')
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# const is disallowed with non-optional arguments
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for nargs in [1, '*', '+']:

‎Misc/NEWS.d/next/Library/2024-10-01-13-11-53.gh-issue-85935.CTwJUy.rst

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,4 @@
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:meth:`argparse.ArgumentParser.add_argument` now raises an exception if
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an :ref:`action` that does not consume arguments (like 'store_const' or
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'store_true') or explicit ``nargs=0`` are specified for positional
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arguments.

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