From 30e211c6e3971ceabc45e62ecc7e82789b743ad9 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Wed, 9 Oct 2024 21:42:48 +0300
Subject: [PATCH] gh-61011: Fix inheritance of nested mutually exclusive groups
 in argparse

Previously, all nested mutually exclusive groups lost their connection
to the group containing them and were displayed as belonging directly
to the parser.

Co-authored-by: Danica J. Sutherland <djsutherland@users.noreply.github.com>
---
 Lib/argparse.py                               |  6 +++-
 Lib/test/test_argparse.py                     | 29 +++++++++++++++++++
 Misc/ACKS                                     |  1 +
 ...4-10-09-21-42-43.gh-issue-61011.pQXZb1.rst |  4 +++
 4 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-10-09-21-42-43.gh-issue-61011.pQXZb1.rst

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 21299b69ecd74c..25b2a532e57e67 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1521,7 +1521,11 @@ 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 1bf812b36fc2c6..57d881796ffca2 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2929,6 +2929,35 @@ 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(prog='PROG', parents=[parent])
+
+        self.assertRaises(ArgumentParserError, parser.parse_args,
+            ['-y', 'Y', '-z', 'Z'])
+
+        parser_help = parser.format_help()
+        self.assertEqual(parser_help, textwrap.dedent('''\
+            usage: PROG [-h] [-w W] [-x X] [-y Y | -z Z]
+
+            options:
+              -h, --help  show this help message and exit
+
+            g:
+              gd
+
+              -w W
+              -x X
+              -y Y
+              -z Z
+        '''))
+
 # ==============================
 # Mutually exclusive group tests
 # ==============================
diff --git a/Misc/ACKS b/Misc/ACKS
index d94cbacf888468..a1769d9601a2ea 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1814,6 +1814,7 @@ Reuben Sumner
 Eryk Sun
 Sanjay Sundaresan
 Marek Šuppa
+Danica J. Sutherland
 Hisao Suzuki
 Kalle Svensson
 Andrew Svetlov
diff --git a/Misc/NEWS.d/next/Library/2024-10-09-21-42-43.gh-issue-61011.pQXZb1.rst b/Misc/NEWS.d/next/Library/2024-10-09-21-42-43.gh-issue-61011.pQXZb1.rst
new file mode 100644
index 00000000000000..20f9c0b9c78b12
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-10-09-21-42-43.gh-issue-61011.pQXZb1.rst
@@ -0,0 +1,4 @@
+Fix inheritance of nested mutually exclusive groups from parent parser in
+:class:`argparse.ArgumentParser`. Previously, all nested mutually exclusive
+groups lost their connection to the group containing them and were displayed
+as belonging directly to the parser.