From d8a5dc85619bcf5f553a809090abe1a57e4a70cb Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Sun, 29 Sep 2024 14:15:03 +0300
Subject: [PATCH] gh-61011: Fix inheriting mutually exclusive groups from
 parent parsers

Co-authored-by: Dougal J. Sutherland
---
 Lib/argparse.py           |  6 +++++-
 Lib/test/test_argparse.py | 30 ++++++++++++++++++++++++++++++
 Misc/ACKS                 |  1 +
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 504289192f3f96..c4f43e7d01bc33 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1514,7 +1514,11 @@ def _add_container_actions(self, container):
         # NOTE: if add_mutually_exclusive_group ever gains title= and
         # description= then this code will need to be expanded as above
         for group in container._mutually_exclusive_groups:
-            mutex_group = self.add_mutually_exclusive_group(
+            if group._container is container:
+                cont = self
+            else:
+                cont = title_group_map[group._container.title]
+            mutex_group = cont.add_mutually_exclusive_group(
                 required=group.required)
 
             # map the actions to their new mutex group
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 15805937baaa97..a1e4eee0852782 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2904,6 +2904,36 @@ def test_groups_parents(self):
     def test_wrong_type_parents(self):
         self.assertRaises(TypeError, ErrorRaisingArgumentParser, parents=[1])
 
+    def test_mutex_groups_parents(self):
+        parent = ErrorRaisingArgumentParser(add_help=False)
+        g = parent.add_argument_group(title='g', description='gd')
+        g.add_argument('-w')
+        g.add_argument('-x')
+        m = g.add_mutually_exclusive_group()
+        m.add_argument('-y')
+        m.add_argument('-z')
+        parser = ErrorRaisingArgumentParser(parents=[parent])
+
+        self.assertRaises(ArgumentParserError, parser.parse_args,
+            ['-y', 'Y', '-z', 'Z'])
+
+        parser_help = parser.format_help()
+        progname = self.main_program
+        self.assertEqual(parser_help, textwrap.dedent('''\
+            usage: {}{}[-h] [-w W] [-x X] [-y Y | -z Z]
+
+            optional arguments:
+              -h, --help  show this help message and exit
+
+            g:
+              gd
+
+              -w W
+              -x X
+              -y Y
+              -z Z
+        '''.format(progname, ' ' if progname else '' )))
+
 # ==============================
 # Mutually exclusive group tests
 # ==============================
diff --git a/Misc/ACKS b/Misc/ACKS
index d94cbacf888468..bc8ece71289c12 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1814,6 +1814,7 @@ Reuben Sumner
 Eryk Sun
 Sanjay Sundaresan
 Marek Šuppa
+Dougal J. Sutherland
 Hisao Suzuki
 Kalle Svensson
 Andrew Svetlov