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30 changes: 29 additions & 1 deletion Doc/library/argparse.rst
Original file line number Diff line number Diff line change
Expand Up @@ -142,7 +142,7 @@ ArgumentParser objects
formatter_class=argparse.HelpFormatter, \
prefix_chars='-', fromfile_prefix_chars=None, \
argument_default=None, conflict_handler='error', \
add_help=True, allow_abbrev=True)
add_help=True, allow_abbrev=True, exit_on_error=True)

Create a new :class:`ArgumentParser` object. All parameters should be passed
as keyword arguments. Each parameter has its own more detailed description
Expand Down Expand Up @@ -179,13 +179,19 @@ ArgumentParser objects
* allow_abbrev_ - Allows long options to be abbreviated if the
abbreviation is unambiguous. (default: ``True``)

* exit_on_error_ - Determines whether or not ArgumentParser exits with
error info when an error occurs. (default: ``True``)

.. versionchanged:: 3.5
*allow_abbrev* parameter was added.

.. versionchanged:: 3.8
In previous versions, *allow_abbrev* also disabled grouping of short
flags such as ``-vv`` to mean ``-v -v``.

.. versionchanged:: 3.9
*exit_on_error* parameter was added.

The following sections describe how each of these are used.


Expand Down Expand Up @@ -647,6 +653,28 @@ the help options::
+h, ++help show this help message and exit


exit_on_error
^^^^^^^^^^^^^

Normally, when you pass an invalid argument list to the :meth:`~ArgumentParser.parse_args`
method of an :class:`ArgumentParser`, it will exit with error info.

If the user would like catch errors manually, the feature can be enable by setting
``exit_on_error`` to ``False``::

>>> parser = argparse.ArgumentParser(exit_on_error=False)
>>> parser.add_argument('--integers', type=int)
_StoreAction(option_strings=['--integers'], dest='integers', nargs=None, const=None, default=None, type=<class 'int'>, choices=None, help=None, metavar=None)
>>> try:
... parser.parse_args('--integers a'.split())
... except argparse.ArgumentError:
... print('Catching an argumentError')
...
Catching an argumentError

.. versionadded:: 3.9


The add_argument() method
-------------------------

Expand Down
26 changes: 17 additions & 9 deletions Lib/argparse.py
Original file line number Diff line number Diff line change
Expand Up @@ -1623,6 +1623,8 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
- conflict_handler -- String indicating how to handle conflicts
- add_help -- Add a -h/-help option
- allow_abbrev -- Allow long options to be abbreviated unambiguously
- exit_on_error -- Determines whether or not ArgumentParser exits with
error info when an error occurs
"""

def __init__(self,
Expand All @@ -1637,7 +1639,8 @@ def __init__(self,
argument_default=None,
conflict_handler='error',
add_help=True,
allow_abbrev=True):
allow_abbrev=True,
exit_on_error=True):

superinit = super(ArgumentParser, self).__init__
superinit(description=description,
Expand All @@ -1656,6 +1659,7 @@ def __init__(self,
self.fromfile_prefix_chars = fromfile_prefix_chars
self.add_help = add_help
self.allow_abbrev = allow_abbrev
self.exit_on_error = exit_on_error

add_group = self.add_argument_group
self._positionals = add_group(_('positional arguments'))
Expand Down Expand Up @@ -1786,15 +1790,19 @@ def parse_known_args(self, args=None, namespace=None):
setattr(namespace, dest, self._defaults[dest])

# parse the arguments and exit if there are any errors
try:
if self.exit_on_error:
try:
namespace, args = self._parse_known_args(args, namespace)
except ArgumentError:
err = _sys.exc_info()[1]
self.error(str(err))
else:
namespace, args = self._parse_known_args(args, namespace)
if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)
return namespace, args
except ArgumentError:
err = _sys.exc_info()[1]
self.error(str(err))

if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)
return namespace, args

def _parse_known_args(self, arg_strings, namespace):
# replace arg strings that are file references
Expand Down
15 changes: 15 additions & 0 deletions Lib/test/test_argparse.py
Original file line number Diff line number Diff line change
Expand Up @@ -5222,6 +5222,21 @@ def test_help_with_metavar(self):
'''))


class TestExitOnError(TestCase):

def setUp(self):
self.parser = argparse.ArgumentParser(exit_on_error=False)
self.parser.add_argument('--integers', metavar='N', type=int)

def test_exit_on_error_with_good_args(self):
ns = self.parser.parse_args('--integers 4'.split())
self.assertEqual(ns, argparse.Namespace(integers=4))

def test_exit_on_error_with_bad_args(self):
with self.assertRaises(argparse.ArgumentError):
self.parser.parse_args('--integers a'.split())


def test_main():
support.run_unittest(__name__)
# Remove global references to avoid looking like we have refleaks.
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Add optional keyword argument ``exit_on_error`` for :class:`ArgumentParser`.