From 6786dbdc25e74c0dcc318e96b4a3b91860c8b71a Mon Sep 17 00:00:00 2001
From: Irit Katriel <iritkatriel@yahoo.com>
Date: Tue, 22 Mar 2022 09:28:35 +0000
Subject: [PATCH] shallow copy the notes in split(), if it's a sequence

---
 Lib/test/test_exception_group.py | 20 ++++++++++++++++++++
 Objects/exceptions.c             | 10 ++++++++++
 2 files changed, 30 insertions(+)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index 15a1659c056158..158c2863b25ef5 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -665,6 +665,26 @@ def exc(ex):
         self.assertMatchesTemplate(
             rest, ExceptionGroup, [ValueError(1)])
 
+    def test_split_copies_notes(self):
+        # make sure each exception group after a split has its own __notes__ list
+        eg = ExceptionGroup("eg", [ValueError(1), TypeError(2)])
+        eg.add_note("note1")
+        eg.add_note("note2")
+        orig_notes = list(eg.__notes__)
+        match, rest = eg.split(TypeError)
+        self.assertEqual(eg.__notes__, orig_notes)
+        self.assertEqual(match.__notes__, orig_notes)
+        self.assertEqual(rest.__notes__, orig_notes)
+        self.assertIsNot(eg.__notes__, match.__notes__)
+        self.assertIsNot(eg.__notes__, rest.__notes__)
+        self.assertIsNot(match.__notes__, rest.__notes__)
+        eg.add_note("eg")
+        match.add_note("match")
+        rest.add_note("rest")
+        self.assertEqual(eg.__notes__, orig_notes + ["eg"])
+        self.assertEqual(match.__notes__, orig_notes + ["match"])
+        self.assertEqual(rest.__notes__, orig_notes + ["rest"])
+
 
 class NestedExceptionGroupSubclassSplitTest(ExceptionGroupSplitTestBase):
 
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 09eb1ed90a88ba..70cdc2d5829cf4 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -923,6 +923,16 @@ exceptiongroup_subset(
         if (notes == NULL) {
             goto error;
         }
+        if (PySequence_Check(notes)) {
+            /* make a copy so the parts have independent notes.
+             * If __notes__ is not a sequence, we don't know how to copy it */
+            PyObject *notes_copy = PySequence_List(notes);
+            Py_DECREF(notes);
+            if (notes_copy == NULL) {
+                goto error;
+            }
+            notes = notes_copy;
+        }
         if (PyObject_SetAttr(eg, &_Py_ID(__notes__), notes) < 0) {
             Py_DECREF(notes);
             goto error;