bpo-22047: [argparse] deprecate nested argument groups and mutually exclusive groups (GH-30098)

2 files changed, 30 insertions, 2 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 8a81801..de95eed 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -89,6 +89,8 @@ import os as _os
 import re as _re
 import sys as _sys
 
+import warnings
+
 from gettext import gettext as _, ngettext
 
 SUPPRESS = '==SUPPRESS=='
@@ -1648,6 +1650,14 @@ class _ArgumentGroup(_ActionsContainer):
         super(_ArgumentGroup, self)._remove_action(action)
         self._group_actions.remove(action)
 
+    def add_argument_group(self, *args, **kwargs):
+        warnings.warn(
+            "Nesting argument groups is deprecated.",
+            category=DeprecationWarning,
+            stacklevel=2
+        )
+        return super().add_argument_group(*args, **kwargs)
+
 
 class _MutuallyExclusiveGroup(_ArgumentGroup):
 
@@ -1668,6 +1678,14 @@ class _MutuallyExclusiveGroup(_ArgumentGroup):
         self._container._remove_action(action)
         self._group_actions.remove(action)
 
+    def add_mutually_exclusive_group(self, *args, **kwargs):
+        warnings.warn(
+            "Nesting mutually exclusive groups is deprecated.",
+            category=DeprecationWarning,
+            stacklevel=2
+        )
+        return super().add_mutually_exclusive_group(*args, **kwargs)
+
 
 class ArgumentParser(_AttributeHolder, _ActionsContainer):
     """Object for parsing command line strings into Python objects.
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index eb37d4d..4c23610 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -9,6 +9,7 @@ import textwrap
 import tempfile
 import unittest
 import argparse
+import warnings
 
 from io import StringIO
 
@@ -2973,15 +2974,24 @@ class TestMutuallyExclusiveOptionalsAndPositionalsMixed(MEMixin, TestCase):
 
 class TestMutuallyExclusiveNested(MEMixin, TestCase):
 
+    # Nesting mutually exclusive groups is an undocumented feature
+    # that came about by accident through inheritance and has been
+    # the source of many bugs. It is deprecated and this test should
+    # eventually be removed along with it.
+
     def get_parser(self, required):
         parser = ErrorRaisingArgumentParser(prog='PROG')
         group = parser.add_mutually_exclusive_group(required=required)
         group.add_argument('-a')
         group.add_argument('-b')
-        group2 = group.add_mutually_exclusive_group(required=required)
+        with warnings.catch_warnings():
+            warnings.simplefilter('ignore', DeprecationWarning)
+            group2 = group.add_mutually_exclusive_group(required=required)
         group2.add_argument('-c')
         group2.add_argument('-d')
-        group3 = group2.add_mutually_exclusive_group(required=required)
+        with warnings.catch_warnings():
+            warnings.simplefilter('ignore', DeprecationWarning)
+            group3 = group2.add_mutually_exclusive_group(required=required)
         group3.add_argument('-e')
         group3.add_argument('-f')
         return parser