shallow copy the notes in split(), if it's a sequence

iritkatriel · iritkatriel · commit 6786dbdc25e7 · 2022-03-22T09:32:30.000Z
diff --git 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
@@ -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;
