pythongh-65865: Raise early errors for invalid help strings in argparse

Lib/argparse.py

@@ -588,17 +588,20 @@ def _format_args(self, action, default_metavar):
  return result
 
  def _expand_help(self, action):
+ help_string = self._get_help_string(action)
+ if '%' not in help_string:
+ return help_string
  params = dict(vars(action), prog=self._prog)
  for name in list(params):
- if params[name] is SUPPRESS:
+ value = params[name]
+ if value is SUPPRESS:
  del params[name]
- for name in list(params):
- if hasattr(params[name], '__name__'):
- params[name] = params[name].__name__
+ elif hasattr(value, '__name__'):
+ params[name] = value.__name__
  if params.get('choices') is not None:
  choices_str = ', '.join([str(c) for c in params['choices']])
  params['choices'] = choices_str
- return self._get_help_string(action) % params
+ return help_string % params
 
  def _iter_indented_subactions(self, action):
  try:
@@ -1180,9 +1183,13 @@ def add_parser(self, name, *, deprecated=False, **kwargs):
  help = kwargs.pop('help')
  choice_action = self._ChoicesPseudoAction(name, aliases, help)
  self._choices_actions.append(choice_action)
+ else:
+ choice_action = None
 
  # create the parser and add it to the map
  parser = self._parser_class(**kwargs)
+ if choice_action is not None:
+ parser._check_help(choice_action)
  self._name_parser_map[name] = parser
 
  # make parser available under aliases also
@@ -1449,11 +1456,12 @@ def add_argument(self, *args, **kwargs):
 
  # raise an error if the metavar does not match the type
  if hasattr(self, "_get_formatter"):
+ formatter = self._get_formatter()
  try:
- self._get_formatter()._format_args(action, None)
+ formatter._format_args(action, None)
  except TypeError:
  raise ValueError("length of metavar tuple does not match nargs")
-
+ self._check_help(action)
  return self._add_action(action)
 
  def add_argument_group(self, *args, **kwargs):
@@ -1631,6 +1639,14 @@ def _handle_conflict_resolve(self, action, conflicting_actions):
  if not action.option_strings:
  action.container._remove_action(action)
 
+ def _check_help(self, action):
+ if action.help and hasattr(self, "_get_formatter"):
+ formatter = self._get_formatter()
+ try:
+ formatter._expand_help(action)
+ except (ValueError, TypeError, KeyError):
+ raise ValueError('badly formed help string')
+
 
 class _ArgumentGroup(_ActionsContainer):
 
@@ -1848,6 +1864,7 @@ def add_subparsers(self, **kwargs):
  # create the parsers action and add it to the positionals list
  parsers_class = self._pop_action_class(kwargs, 'parsers')
  action = parsers_class(option_strings=[], **kwargs)
+ self._check_help(action)
  self._subparsers._add_action(action)
 
  # return the created parsers action

Lib/test/test_argparse.py

@@ -2610,6 +2610,27 @@ def test_parser_command_help(self):
  --foo foo help
  '''))
 
+ def test_invalid_subparsers_help(self):
+ parser = ErrorRaisingArgumentParser(prog='PROG')
+ with self.assertRaisesRegex(ValueError, 'badly formed help string'):
+ parser.add_subparsers(help='%Y-%m-%d')
+ parser = ErrorRaisingArgumentParser(prog='PROG')
+ with self.assertRaisesRegex(ValueError, 'badly formed help string'):
+ parser.add_subparsers(help='%(spam)s')
+ parser = ErrorRaisingArgumentParser(prog='PROG')
+ with self.assertRaisesRegex(ValueError, 'badly formed help string'):
+ parser.add_subparsers(help='%(prog)d')
+
+ def test_invalid_subparser_help(self):
+ parser = ErrorRaisingArgumentParser(prog='PROG')
+ subparsers = parser.add_subparsers()
+ with self.assertRaisesRegex(ValueError, 'badly formed help string'):
+ subparsers.add_parser('1', help='%Y-%m-%d')
+ with self.assertRaisesRegex(ValueError, 'badly formed help string'):
+ subparsers.add_parser('1', help='%(spam)s')
+ with self.assertRaisesRegex(ValueError, 'badly formed help string'):
+ subparsers.add_parser('1', help='%(prog)d')
+
  def test_subparser_title_help(self):
  parser = ErrorRaisingArgumentParser(prog='PROG',
  description='main description')
@@ -5333,6 +5354,14 @@ def test_invalid_action(self):
  self.assertValueError('--foo', action="store-true",
  errmsg='unknown action')
 
+ def test_invalid_help(self):
+ self.assertValueError('--foo', help='%Y-%m-%d',
+ errmsg='badly formed help string')
+ self.assertValueError('--foo', help='%(spam)s',
+ errmsg='badly formed help string')
+ self.assertValueError('--foo', help='%(prog)d',
+ errmsg='badly formed help string')
+
  def test_multiple_dest(self):
  parser = argparse.ArgumentParser()
  parser.add_argument(dest='foo')

Misc/NEWS.d/next/Library/2024-10-02-16-35-07.gh-issue-65865.S2D4wq.rst

@@ -0,0 +1,3 @@
+:mod:`argparse` now raises early error for invalid ``help`` arguments to
+:meth:`~argparse.ArgumentParser.add_argument`,
+:meth:`~argparse.ArgumentParser.add_subparsers` and :meth:`!add_parser`.