From b1afcb8806ae481f5c5bb13c00111b282dc0775c Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 19 Nov 2025 16:27:47 +1030
Subject: [PATCH 01/41] Use `self.exceptions` in `BaseExceptionGroup` repr by
 supporting custom reprs in `ComplexExtendsException`

---
 Objects/exceptions.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 244d8f39e2bae5..0dd7e4c4a2125c 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -694,12 +694,12 @@ PyTypeObject _PyExc_ ## EXCNAME = { \
 
 #define ComplexExtendsException(EXCBASE, EXCNAME, EXCSTORE, EXCNEW, \
                                 EXCMETHODS, EXCMEMBERS, EXCGETSET, \
-                                EXCSTR, EXCDOC) \
+                                EXCSTR, EXCREPR, EXCDOC) \
 static PyTypeObject _PyExc_ ## EXCNAME = { \
     PyVarObject_HEAD_INIT(NULL, 0) \
     # EXCNAME, \
     sizeof(Py ## EXCSTORE ## Object), 0, \
-    EXCSTORE ## _dealloc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
+    EXCSTORE ## _dealloc, 0, 0, 0, 0, EXCREPR, 0, 0, 0, 0, 0, \
     EXCSTR, 0, 0, 0, \
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, \
     PyDoc_STR(EXCDOC), EXCSTORE ## _traverse, \
@@ -792,7 +792,7 @@ StopIteration_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 ComplexExtendsException(PyExc_Exception, StopIteration, StopIteration,
-                        0, 0, StopIteration_members, 0, 0,
+                        0, 0, StopIteration_members, 0, 0, 0,
                         "Signal the end from iterator.__next__().");
 
 
@@ -865,7 +865,7 @@ static PyMemberDef SystemExit_members[] = {
 };
 
 ComplexExtendsException(PyExc_BaseException, SystemExit, SystemExit,
-                        0, 0, SystemExit_members, 0, 0,
+                        0, 0, SystemExit_members, 0, 0, 0,
                         "Request to exit from the interpreter.");
 
 /*
@@ -1063,6 +1063,19 @@ BaseExceptionGroup_str(PyObject *op)
         self->msg, num_excs, num_excs > 1 ? "s" : "");
 }
 
+static PyObject *
+BaseExceptionGroup_repr(PyObject *op)
+{
+    PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
+    assert(self->msg);
+    assert(self->excs);
+
+    const char *name = _PyType_Name(Py_TYPE(self));
+    return PyUnicode_FromFormat(
+        "%s(%R, %R)", name,
+        self->msg, self->excs);
+}
+
 /*[clinic input]
 @critical_section
 BaseExceptionGroup.derive
@@ -1697,7 +1710,7 @@ static PyMethodDef BaseExceptionGroup_methods[] = {
 ComplexExtendsException(PyExc_BaseException, BaseExceptionGroup,
     BaseExceptionGroup, BaseExceptionGroup_new /* new */,
     BaseExceptionGroup_methods, BaseExceptionGroup_members,
-    0 /* getset */, BaseExceptionGroup_str,
+    0 /* getset */, BaseExceptionGroup_str, BaseExceptionGroup_repr,
     "A combination of multiple unrelated exceptions.");
 
 /*
@@ -2425,7 +2438,7 @@ static PyGetSetDef OSError_getset[] = {
 ComplexExtendsException(PyExc_Exception, OSError,
                         OSError, OSError_new,
                         OSError_methods, OSError_members, OSError_getset,
-                        OSError_str,
+                        OSError_str, 0,
                         "Base class for I/O related errors.");
 
 
@@ -2566,7 +2579,7 @@ static PyMethodDef NameError_methods[] = {
 ComplexExtendsException(PyExc_Exception, NameError,
                         NameError, 0,
                         NameError_methods, NameError_members,
-                        0, BaseException_str, "Name not found globally.");
+                        0, BaseException_str, 0, "Name not found globally.");
 
 /*
  *    UnboundLocalError extends NameError
@@ -2700,7 +2713,7 @@ static PyMethodDef AttributeError_methods[] = {
 ComplexExtendsException(PyExc_Exception, AttributeError,
                         AttributeError, 0,
                         AttributeError_methods, AttributeError_members,
-                        0, BaseException_str, "Attribute not found.");
+                        0, BaseException_str, 0, "Attribute not found.");
 
 /*
  *    SyntaxError extends Exception
@@ -2899,7 +2912,7 @@ static PyMemberDef SyntaxError_members[] = {
 
 ComplexExtendsException(PyExc_Exception, SyntaxError, SyntaxError,
                         0, 0, SyntaxError_members, 0,
-                        SyntaxError_str, "Invalid syntax.");
+                        SyntaxError_str, 0, "Invalid syntax.");
 
 
 /*
@@ -2959,7 +2972,7 @@ KeyError_str(PyObject *op)
 }
 
 ComplexExtendsException(PyExc_LookupError, KeyError, BaseException,
-                        0, 0, 0, 0, KeyError_str, "Mapping key not found.");
+                        0, 0, 0, 0, KeyError_str, 0, "Mapping key not found.");
 
 
 /*

From 59bc3c790b0a05302f94a53361c2a5e636f68a15 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 19 Nov 2025 16:28:23 +1030
Subject: [PATCH 02/41] Update `ExceptionGroup` tests for new repr and add
 mutation test

---
 Lib/test/test_exception_group.py | 45 +++++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 15 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index 5df2c41c6b56bc..c4cbc36d2fb7de 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -131,12 +131,17 @@ class MyBEG(BaseExceptionGroup):
 
 class StrAndReprTests(unittest.TestCase):
     def test_ExceptionGroup(self):
+        eg_excs = [ValueError(1), TypeError(2)]
         eg = BaseExceptionGroup(
-            'flat', [ValueError(1), TypeError(2)])
+            'flat', eg_excs)
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg),
-            "ExceptionGroup('flat', [ValueError(1), TypeError(2)])")
+            "ExceptionGroup('flat', (ValueError(1), TypeError(2)))")
+
+        # Mutate the list of exceptions passed to BaseExceptionGroup.
+        # This shouldn't change the EG's functionality, nor its repr.
+        eg_excs.clear()
 
         eg = BaseExceptionGroup(
             'nested', [eg, ValueError(1), eg, TypeError(2)])
@@ -144,21 +149,26 @@ def test_ExceptionGroup(self):
         self.assertEqual(str(eg), "nested (4 sub-exceptions)")
         self.assertEqual(repr(eg),
             "ExceptionGroup('nested', "
-                "[ExceptionGroup('flat', "
-                    "[ValueError(1), TypeError(2)]), "
+                "(ExceptionGroup('flat', "
+                    "(ValueError(1), TypeError(2))), "
                  "ValueError(1), "
                  "ExceptionGroup('flat', "
-                    "[ValueError(1), TypeError(2)]), TypeError(2)])")
+                    "(ValueError(1), TypeError(2))), TypeError(2)))")
 
     def test_BaseExceptionGroup(self):
+        eg_excs = [ValueError(1), KeyboardInterrupt(2)]
         eg = BaseExceptionGroup(
-            'flat', [ValueError(1), KeyboardInterrupt(2)])
+            'flat', eg_excs)
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg),
             "BaseExceptionGroup("
                 "'flat', "
-                "[ValueError(1), KeyboardInterrupt(2)])")
+                "(ValueError(1), KeyboardInterrupt(2)))")
+
+        # Mutate the list of exceptions passed to BaseExceptionGroup.
+        # This shouldn't change the EG's functionality, nor its repr.
+        eg_excs.clear()
 
         eg = BaseExceptionGroup(
             'nested', [eg, ValueError(1), eg])
@@ -166,21 +176,26 @@ def test_BaseExceptionGroup(self):
         self.assertEqual(str(eg), "nested (3 sub-exceptions)")
         self.assertEqual(repr(eg),
             "BaseExceptionGroup('nested', "
-                "[BaseExceptionGroup('flat', "
-                    "[ValueError(1), KeyboardInterrupt(2)]), "
+                "(BaseExceptionGroup('flat', "
+                    "(ValueError(1), KeyboardInterrupt(2))), "
                 "ValueError(1), "
                 "BaseExceptionGroup('flat', "
-                    "[ValueError(1), KeyboardInterrupt(2)])])")
+                    "(ValueError(1), KeyboardInterrupt(2)))))")
 
     def test_custom_exception(self):
         class MyEG(ExceptionGroup):
             pass
 
+        eg_excs = [ValueError(1), TypeError(2)]
         eg = MyEG(
-            'flat', [ValueError(1), TypeError(2)])
+            'flat', eg_excs)
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
-        self.assertEqual(repr(eg), "MyEG('flat', [ValueError(1), TypeError(2)])")
+        self.assertEqual(repr(eg), "MyEG('flat', (ValueError(1), TypeError(2)))")
+
+        # Mutate the list of exceptions passed to BaseExceptionGroup.
+        # This shouldn't change the EG's functionality, nor its repr.
+        eg_excs.clear()
 
         eg = MyEG(
             'nested', [eg, ValueError(1), eg, TypeError(2)])
@@ -188,10 +203,10 @@ class MyEG(ExceptionGroup):
         self.assertEqual(str(eg), "nested (4 sub-exceptions)")
         self.assertEqual(repr(eg), (
                  "MyEG('nested', "
-                     "[MyEG('flat', [ValueError(1), TypeError(2)]), "
+                     "(MyEG('flat', (ValueError(1), TypeError(2))), "
                       "ValueError(1), "
-                      "MyEG('flat', [ValueError(1), TypeError(2)]), "
-                      "TypeError(2)])"))
+                      "MyEG('flat', (ValueError(1), TypeError(2))), "
+                      "TypeError(2)))"))
 
 
 def create_simple_eg():

From ca2d21da242bfec684109d03923a7d063f866095 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 19 Nov 2025 16:30:19 +1030
Subject: [PATCH 03/41] Fix typo in test comment

---
 Lib/test/test_exception_group.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index c4cbc36d2fb7de..b8ca7935c2618d 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -193,7 +193,7 @@ class MyEG(ExceptionGroup):
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg), "MyEG('flat', (ValueError(1), TypeError(2)))")
 
-        # Mutate the list of exceptions passed to BaseExceptionGroup.
+        # Mutate the list of exceptions passed to MyEG.
         # This shouldn't change the EG's functionality, nor its repr.
         eg_excs.clear()
 

From 493ab01143fe412892781704d0127d120f064092 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 19 Nov 2025 16:35:13 +1030
Subject: [PATCH 04/41] Update docs for `BaseExceptionGroup` repr change

---
 Doc/library/exceptions.rst       | 6 +++---
 Doc/reference/compound_stmts.rst | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst
index 16d42c010f6df0..22715c979ab8f2 100644
--- a/Doc/library/exceptions.rst
+++ b/Doc/library/exceptions.rst
@@ -1053,11 +1053,11 @@ their subgroups based on the types of the contained exceptions.
          ...
          >>> match, rest = exc.split(ValueError)
          >>> exc, exc.__context__, exc.__cause__, exc.__notes__
-         (MyGroup('eg', [ValueError(1), TypeError(2)]), Exception('context'), Exception('cause'), ['a note'])
+         (MyGroup('eg', (ValueError(1), TypeError(2))), Exception('context'), Exception('cause'), ['a note'])
          >>> match, match.__context__, match.__cause__, match.__notes__
-         (MyGroup('eg', [ValueError(1)]), Exception('context'), Exception('cause'), ['a note'])
+         (MyGroup('eg', (ValueError(1),)), Exception('context'), Exception('cause'), ['a note'])
          >>> rest, rest.__context__, rest.__cause__, rest.__notes__
-         (MyGroup('eg', [TypeError(2)]), Exception('context'), Exception('cause'), ['a note'])
+         (MyGroup('eg', (TypeError(2),)), Exception('context'), Exception('cause'), ['a note'])
          >>> exc.__traceback__ is match.__traceback__ is rest.__traceback__
          True
 
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
index 6521b4bee50758..861c221502ed4d 100644
--- a/Doc/reference/compound_stmts.rst
+++ b/Doc/reference/compound_stmts.rst
@@ -388,7 +388,7 @@ type of the target ``e`` is consistently :exc:`BaseExceptionGroup`::
    ... except* BlockingIOError as e:
    ...     print(repr(e))
    ...
-   ExceptionGroup('', (BlockingIOError()))
+   ExceptionGroup('', (BlockingIOError(),))
 
 :keyword:`break`, :keyword:`continue` and :keyword:`return`
 cannot appear in an :keyword:`!except*` clause.

From cd90d51c63fb4d6e7e3bf91fe8b439f06400c57d Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 19 Nov 2025 16:40:27 +1030
Subject: [PATCH 05/41] Add NEWS entry

---
 .../2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst              | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
new file mode 100644
index 00000000000000..17848e65bac76c
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
@@ -0,0 +1,2 @@
+Ensure the repr for :exc:`ExceptionGroup` and :exc:`BaseExceptionGroup` does
+not change when its original exception list is mutated.

From 177b5355281af76c495c952f9720f68aae228f06 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 19 Nov 2025 17:06:45 +1030
Subject: [PATCH 06/41] Update `ExceptionGroup` repr in `test_traceback`

---
 Lib/test/test_traceback.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index bf57867a8715c0..921be6374fe810 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5170,7 +5170,7 @@ def expected(t, m, fn, l, f, E, e, z):
                 f'  |   File {fn}"{__file__}"{z}, line {l}{lno_foo+9}{z}, in {f}test_colorized_traceback_from_exception_group{z}',
                 f'  |     {e}foo{z}{E}(){z}',
                 f'  |     {e}~~~{z}{E}^^{z}',
-                f"  |     e = ExceptionGroup('test', [ZeroDivisionError('division by zero')])",
+                f"  |     e = ExceptionGroup('test', (ZeroDivisionError('division by zero'),))",
                 f"  |     foo = {foo}",
                 f'  |     self = <{__name__}.TestColorizedTraceback testMethod=test_colorized_traceback_from_exception_group>',
                 f'  |   File {fn}"{__file__}"{z}, line {l}{lno_foo+6}{z}, in {f}foo{z}',

From af4f086abb9a5c19203b564e8e1b19965d2fbd6a Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Fri, 21 Nov 2025 18:26:52 +1030
Subject: [PATCH 07/41] Revert "Update `ExceptionGroup` repr in
 `test_traceback`"

This reverts commit 177b5355281af76c495c952f9720f68aae228f06.
---
 Lib/test/test_traceback.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 921be6374fe810..bf57867a8715c0 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5170,7 +5170,7 @@ def expected(t, m, fn, l, f, E, e, z):
                 f'  |   File {fn}"{__file__}"{z}, line {l}{lno_foo+9}{z}, in {f}test_colorized_traceback_from_exception_group{z}',
                 f'  |     {e}foo{z}{E}(){z}',
                 f'  |     {e}~~~{z}{E}^^{z}',
-                f"  |     e = ExceptionGroup('test', (ZeroDivisionError('division by zero'),))",
+                f"  |     e = ExceptionGroup('test', [ZeroDivisionError('division by zero')])",
                 f"  |     foo = {foo}",
                 f'  |     self = <{__name__}.TestColorizedTraceback testMethod=test_colorized_traceback_from_exception_group>',
                 f'  |   File {fn}"{__file__}"{z}, line {l}{lno_foo+6}{z}, in {f}foo{z}',

From 72918ead960e643aa76bfb43b27fa6a8fc1a9911 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Fri, 21 Nov 2025 18:29:47 +1030
Subject: [PATCH 08/41] Update `ExceptionGroup` tests to no longer change the
 repr

---
 Lib/test/test_exception_group.py | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index b8ca7935c2618d..d8f53bb8616331 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -137,7 +137,7 @@ def test_ExceptionGroup(self):
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg),
-            "ExceptionGroup('flat', (ValueError(1), TypeError(2)))")
+            "ExceptionGroup('flat', [ValueError(1), TypeError(2)])")
 
         # Mutate the list of exceptions passed to BaseExceptionGroup.
         # This shouldn't change the EG's functionality, nor its repr.
@@ -149,11 +149,11 @@ def test_ExceptionGroup(self):
         self.assertEqual(str(eg), "nested (4 sub-exceptions)")
         self.assertEqual(repr(eg),
             "ExceptionGroup('nested', "
-                "(ExceptionGroup('flat', "
-                    "(ValueError(1), TypeError(2))), "
+                "[ExceptionGroup('flat', "
+                    "[ValueError(1), TypeError(2)]), "
                  "ValueError(1), "
                  "ExceptionGroup('flat', "
-                    "(ValueError(1), TypeError(2))), TypeError(2)))")
+                    "[ValueError(1), TypeError(2)]), TypeError(2)])")
 
     def test_BaseExceptionGroup(self):
         eg_excs = [ValueError(1), KeyboardInterrupt(2)]
@@ -164,7 +164,7 @@ def test_BaseExceptionGroup(self):
         self.assertEqual(repr(eg),
             "BaseExceptionGroup("
                 "'flat', "
-                "(ValueError(1), KeyboardInterrupt(2)))")
+                "[ValueError(1), KeyboardInterrupt(2)])")
 
         # Mutate the list of exceptions passed to BaseExceptionGroup.
         # This shouldn't change the EG's functionality, nor its repr.
@@ -176,11 +176,11 @@ def test_BaseExceptionGroup(self):
         self.assertEqual(str(eg), "nested (3 sub-exceptions)")
         self.assertEqual(repr(eg),
             "BaseExceptionGroup('nested', "
-                "(BaseExceptionGroup('flat', "
-                    "(ValueError(1), KeyboardInterrupt(2))), "
+                "[BaseExceptionGroup('flat', "
+                    "[ValueError(1), KeyboardInterrupt(2)]), "
                 "ValueError(1), "
                 "BaseExceptionGroup('flat', "
-                    "(ValueError(1), KeyboardInterrupt(2)))))")
+                    "[ValueError(1), KeyboardInterrupt(2)])])")
 
     def test_custom_exception(self):
         class MyEG(ExceptionGroup):
@@ -191,7 +191,7 @@ class MyEG(ExceptionGroup):
             'flat', eg_excs)
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
-        self.assertEqual(repr(eg), "MyEG('flat', (ValueError(1), TypeError(2)))")
+        self.assertEqual(repr(eg), "MyEG('flat', [ValueError(1), TypeError(2)])")
 
         # Mutate the list of exceptions passed to MyEG.
         # This shouldn't change the EG's functionality, nor its repr.
@@ -203,10 +203,10 @@ class MyEG(ExceptionGroup):
         self.assertEqual(str(eg), "nested (4 sub-exceptions)")
         self.assertEqual(repr(eg), (
                  "MyEG('nested', "
-                     "(MyEG('flat', (ValueError(1), TypeError(2))), "
+                     "[MyEG('flat', [ValueError(1), TypeError(2)]), "
                       "ValueError(1), "
-                      "MyEG('flat', (ValueError(1), TypeError(2))), "
-                      "TypeError(2)))"))
+                      "MyEG('flat', [ValueError(1), TypeError(2)]), "
+                      "TypeError(2)])"))
 
 
 def create_simple_eg():

From b45402ab026aafa15c2311376cd7136a2daf6bdd Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sat, 22 Nov 2025 06:34:55 +1030
Subject: [PATCH 09/41] Store exceptions copy in
 `BaseExceptionGroup->excs_orig` and use in `repr`

---
 Include/cpython/pyerrors.h |  1 +
 Objects/exceptions.c       | 24 ++++++++++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/Include/cpython/pyerrors.h b/Include/cpython/pyerrors.h
index 6b63d304b0d929..9e0b58526fd7b3 100644
--- a/Include/cpython/pyerrors.h
+++ b/Include/cpython/pyerrors.h
@@ -18,6 +18,7 @@ typedef struct {
     PyException_HEAD
     PyObject *msg;
     PyObject *excs;
+    PyObject *excs_orig;
 } PyBaseExceptionGroupObject;
 
 typedef struct {
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 0dd7e4c4a2125c..c0db185635a891 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -905,12 +905,22 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
-    exceptions = PySequence_Tuple(exceptions);
+    /* Make a copy of the passed exceptions sequence, for use in the repr */
+    PyObject *exceptions_copy = exceptions;
+    if (PyList_Check(exceptions)) {
+        exceptions_copy = PySequence_List(exceptions);
+    } else {
+        Py_INCREF(exceptions_copy);
+    }
+
+    exceptions = PySequence_Tuple(exceptions_copy);
     if (!exceptions) {
         return NULL;
     }
 
-    /* We are now holding a ref to the exceptions tuple */
+    /* We are now holding a ref to (a potential copy of) the original
+     * exceptions sequence and to the exceptions tuple.
+     */
 
     Py_ssize_t numexcs = PyTuple_GET_SIZE(exceptions);
     if (numexcs == 0) {
@@ -988,9 +998,11 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
     self->msg = Py_NewRef(message);
     self->excs = exceptions;
+    self->excs_orig = exceptions_copy;
     return (PyObject*)self;
 error:
     Py_DECREF(exceptions);
+    Py_DECREF(exceptions_copy);
     return NULL;
 }
 
@@ -1029,6 +1041,7 @@ BaseExceptionGroup_clear(PyObject *op)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     Py_CLEAR(self->msg);
     Py_CLEAR(self->excs);
+    Py_CLEAR(self->excs_orig);
     return BaseException_clear(op);
 }
 
@@ -1046,6 +1059,7 @@ BaseExceptionGroup_traverse(PyObject *op, visitproc visit, void *arg)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     Py_VISIT(self->msg);
     Py_VISIT(self->excs);
+    Py_VISIT(self->excs_orig);
     return BaseException_traverse(op, visit, arg);
 }
 
@@ -1068,12 +1082,12 @@ BaseExceptionGroup_repr(PyObject *op)
 {
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     assert(self->msg);
-    assert(self->excs);
+    assert(self->excs_orig);
 
     const char *name = _PyType_Name(Py_TYPE(self));
     return PyUnicode_FromFormat(
         "%s(%R, %R)", name,
-        self->msg, self->excs);
+        self->msg, self->excs_orig);
 }
 
 /*[clinic input]
@@ -1695,6 +1709,8 @@ static PyMemberDef BaseExceptionGroup_members[] = {
         PyDoc_STR("exception message")},
     {"exceptions", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs), Py_READONLY,
         PyDoc_STR("nested exceptions")},
+    {"_excs_orig", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs_orig), Py_READONLY,
+        PyDoc_STR("private copy of original nested exceptions")},
     {NULL}  /* Sentinel */
 };
 

From 62d72a40817eae379bcd175c749e6c2e46cc9a99 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sat, 22 Nov 2025 06:43:17 +1030
Subject: [PATCH 10/41] Revert "Update docs for `BaseExceptionGroup` repr
 change"

This reverts commit 493ab01143fe412892781704d0127d120f064092.
---
 Doc/library/exceptions.rst       | 6 +++---
 Doc/reference/compound_stmts.rst | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst
index 22715c979ab8f2..16d42c010f6df0 100644
--- a/Doc/library/exceptions.rst
+++ b/Doc/library/exceptions.rst
@@ -1053,11 +1053,11 @@ their subgroups based on the types of the contained exceptions.
          ...
          >>> match, rest = exc.split(ValueError)
          >>> exc, exc.__context__, exc.__cause__, exc.__notes__
-         (MyGroup('eg', (ValueError(1), TypeError(2))), Exception('context'), Exception('cause'), ['a note'])
+         (MyGroup('eg', [ValueError(1), TypeError(2)]), Exception('context'), Exception('cause'), ['a note'])
          >>> match, match.__context__, match.__cause__, match.__notes__
-         (MyGroup('eg', (ValueError(1),)), Exception('context'), Exception('cause'), ['a note'])
+         (MyGroup('eg', [ValueError(1)]), Exception('context'), Exception('cause'), ['a note'])
          >>> rest, rest.__context__, rest.__cause__, rest.__notes__
-         (MyGroup('eg', (TypeError(2),)), Exception('context'), Exception('cause'), ['a note'])
+         (MyGroup('eg', [TypeError(2)]), Exception('context'), Exception('cause'), ['a note'])
          >>> exc.__traceback__ is match.__traceback__ is rest.__traceback__
          True
 
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
index 861c221502ed4d..6521b4bee50758 100644
--- a/Doc/reference/compound_stmts.rst
+++ b/Doc/reference/compound_stmts.rst
@@ -388,7 +388,7 @@ type of the target ``e`` is consistently :exc:`BaseExceptionGroup`::
    ... except* BlockingIOError as e:
    ...     print(repr(e))
    ...
-   ExceptionGroup('', (BlockingIOError(),))
+   ExceptionGroup('', (BlockingIOError()))
 
 :keyword:`break`, :keyword:`continue` and :keyword:`return`
 cannot appear in an :keyword:`!except*` clause.

From f93ae8f9e92bb2f7056f6b06114b8b6825b1c76e Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sat, 22 Nov 2025 07:10:51 +1030
Subject: [PATCH 11/41] Remove `BaseExceptionGroup->excs_orig` and reconstruct
 in `repr` instead

---
 Include/cpython/pyerrors.h |  1 -
 Objects/exceptions.c       | 29 +++++++++--------------------
 2 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/Include/cpython/pyerrors.h b/Include/cpython/pyerrors.h
index 9e0b58526fd7b3..6b63d304b0d929 100644
--- a/Include/cpython/pyerrors.h
+++ b/Include/cpython/pyerrors.h
@@ -18,7 +18,6 @@ typedef struct {
     PyException_HEAD
     PyObject *msg;
     PyObject *excs;
-    PyObject *excs_orig;
 } PyBaseExceptionGroupObject;
 
 typedef struct {
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index c0db185635a891..be3dfcda35e449 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -905,22 +905,12 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
-    /* Make a copy of the passed exceptions sequence, for use in the repr */
-    PyObject *exceptions_copy = exceptions;
-    if (PyList_Check(exceptions)) {
-        exceptions_copy = PySequence_List(exceptions);
-    } else {
-        Py_INCREF(exceptions_copy);
-    }
-
-    exceptions = PySequence_Tuple(exceptions_copy);
+    exceptions = PySequence_Tuple(exceptions);
     if (!exceptions) {
         return NULL;
     }
 
-    /* We are now holding a ref to (a potential copy of) the original
-     * exceptions sequence and to the exceptions tuple.
-     */
+    /* We are now holding a ref to the exceptions tuple */
 
     Py_ssize_t numexcs = PyTuple_GET_SIZE(exceptions);
     if (numexcs == 0) {
@@ -998,11 +988,9 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
     self->msg = Py_NewRef(message);
     self->excs = exceptions;
-    self->excs_orig = exceptions_copy;
     return (PyObject*)self;
 error:
     Py_DECREF(exceptions);
-    Py_DECREF(exceptions_copy);
     return NULL;
 }
 
@@ -1041,7 +1029,6 @@ BaseExceptionGroup_clear(PyObject *op)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     Py_CLEAR(self->msg);
     Py_CLEAR(self->excs);
-    Py_CLEAR(self->excs_orig);
     return BaseException_clear(op);
 }
 
@@ -1059,7 +1046,6 @@ BaseExceptionGroup_traverse(PyObject *op, visitproc visit, void *arg)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     Py_VISIT(self->msg);
     Py_VISIT(self->excs);
-    Py_VISIT(self->excs_orig);
     return BaseException_traverse(op, visit, arg);
 }
 
@@ -1082,12 +1068,17 @@ BaseExceptionGroup_repr(PyObject *op)
 {
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     assert(self->msg);
-    assert(self->excs_orig);
+    assert(self->excs);
+
+    PyObject* excs_orig = PyTuple_GET_ITEM(self->args, 1);
+    if (PyList_Check(excs_orig)) {
+        excs_orig = PySequence_List(self->excs);
+    }
 
     const char *name = _PyType_Name(Py_TYPE(self));
     return PyUnicode_FromFormat(
         "%s(%R, %R)", name,
-        self->msg, self->excs_orig);
+        self->msg, excs_orig);
 }
 
 /*[clinic input]
@@ -1709,8 +1700,6 @@ static PyMemberDef BaseExceptionGroup_members[] = {
         PyDoc_STR("exception message")},
     {"exceptions", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs), Py_READONLY,
         PyDoc_STR("nested exceptions")},
-    {"_excs_orig", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs_orig), Py_READONLY,
-        PyDoc_STR("private copy of original nested exceptions")},
     {NULL}  /* Sentinel */
 };
 

From 56eefeef1d10e157b39517ed1fc1ec8c22917d24 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sat, 22 Nov 2025 07:13:50 +1030
Subject: [PATCH 12/41] Ensure that the exceptions copy in `BaseExceptionGroup`
 repr is freed

---
 Objects/exceptions.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index be3dfcda35e449..4de5f8494e1961 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1073,12 +1073,17 @@ BaseExceptionGroup_repr(PyObject *op)
     PyObject* excs_orig = PyTuple_GET_ITEM(self->args, 1);
     if (PyList_Check(excs_orig)) {
         excs_orig = PySequence_List(self->excs);
+    } else {
+        Py_INCREF(excs_orig);
     }
 
     const char *name = _PyType_Name(Py_TYPE(self));
-    return PyUnicode_FromFormat(
+    PyObject *repr = PyUnicode_FromFormat(
         "%s(%R, %R)", name,
         self->msg, excs_orig);
+
+    Py_DECREF(excs_orig);
+    return repr;
 }
 
 /*[clinic input]

From 79dd61534b8cbdf92e0776ee46d09e2473a2bdc5 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sat, 22 Nov 2025 17:05:30 +1030
Subject: [PATCH 13/41] Move `ExceptionGroup` repr tests into new function

---
 Lib/test/test_exception_group.py | 43 +++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index d8f53bb8616331..f49f7b27239989 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -131,18 +131,13 @@ class MyBEG(BaseExceptionGroup):
 
 class StrAndReprTests(unittest.TestCase):
     def test_ExceptionGroup(self):
-        eg_excs = [ValueError(1), TypeError(2)]
         eg = BaseExceptionGroup(
-            'flat', eg_excs)
+            'flat', [ValueError(1), TypeError(2)])
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg),
             "ExceptionGroup('flat', [ValueError(1), TypeError(2)])")
 
-        # Mutate the list of exceptions passed to BaseExceptionGroup.
-        # This shouldn't change the EG's functionality, nor its repr.
-        eg_excs.clear()
-
         eg = BaseExceptionGroup(
             'nested', [eg, ValueError(1), eg, TypeError(2)])
 
@@ -156,9 +151,8 @@ def test_ExceptionGroup(self):
                     "[ValueError(1), TypeError(2)]), TypeError(2)])")
 
     def test_BaseExceptionGroup(self):
-        eg_excs = [ValueError(1), KeyboardInterrupt(2)]
         eg = BaseExceptionGroup(
-            'flat', eg_excs)
+            'flat', [ValueError(1), KeyboardInterrupt(2)])
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg),
@@ -166,10 +160,6 @@ def test_BaseExceptionGroup(self):
                 "'flat', "
                 "[ValueError(1), KeyboardInterrupt(2)])")
 
-        # Mutate the list of exceptions passed to BaseExceptionGroup.
-        # This shouldn't change the EG's functionality, nor its repr.
-        eg_excs.clear()
-
         eg = BaseExceptionGroup(
             'nested', [eg, ValueError(1), eg])
 
@@ -186,17 +176,12 @@ def test_custom_exception(self):
         class MyEG(ExceptionGroup):
             pass
 
-        eg_excs = [ValueError(1), TypeError(2)]
         eg = MyEG(
-            'flat', eg_excs)
+            'flat', [ValueError(1), TypeError(2)])
 
         self.assertEqual(str(eg), "flat (2 sub-exceptions)")
         self.assertEqual(repr(eg), "MyEG('flat', [ValueError(1), TypeError(2)])")
 
-        # Mutate the list of exceptions passed to MyEG.
-        # This shouldn't change the EG's functionality, nor its repr.
-        eg_excs.clear()
-
         eg = MyEG(
             'nested', [eg, ValueError(1), eg, TypeError(2)])
 
@@ -208,6 +193,28 @@ class MyEG(ExceptionGroup):
                       "MyEG('flat', [ValueError(1), TypeError(2)]), "
                       "TypeError(2)])"))
 
+    def test_exceptions_mutation(self):
+        class MyEG(ExceptionGroup):
+            pass
+
+        excs = [ValueError(1), TypeError(2)]
+        eg = MyEG('test', excs)
+
+        self.assertEqual(repr(eg), "MyEG('test', [ValueError(1), TypeError(2)])")
+        excs.clear()
+
+        # Ensure that clearing the exceptions sequence doesn't change the repr.
+        self.assertEqual(repr(eg), "MyEG('test', [ValueError(1), TypeError(2)])")
+
+        # Ensure that the args are still as passed.
+        self.assertEqual(eg.args, ('test', []))
+
+        excs = (ValueError(1), KeyboardInterrupt(2))
+        eg = BaseExceptionGroup('test', excs)
+
+        # Ensure that other, immutable, sequences still work fine.
+        self.assertEqual(repr(eg), "BaseExceptionGroup('test', (ValueError(1), KeyboardInterrupt(2)))")
+
 
 def create_simple_eg():
     excs = []

From e9fec3d944e5fa264955b8c54b082f9ea26d51cd Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sun, 23 Nov 2025 07:36:42 +1030
Subject: [PATCH 14/41] Use the exceptions tuple for all non-lists in
 `ExceptionGroup` repr

---
 Objects/exceptions.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 4de5f8494e1961..a9a053dc350699 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1070,11 +1070,13 @@ BaseExceptionGroup_repr(PyObject *op)
     assert(self->msg);
     assert(self->excs);
 
+    /* Use the actual exceptions tuple for accuracy, but make it look like the
+     * original exception sequence, if possible, for backwards compatibility. */
     PyObject* excs_orig = PyTuple_GET_ITEM(self->args, 1);
     if (PyList_Check(excs_orig)) {
         excs_orig = PySequence_List(self->excs);
     } else {
-        Py_INCREF(excs_orig);
+        excs_orig = Py_NewRef(self->excs);
     }
 
     const char *name = _PyType_Name(Py_TYPE(self));

From f5acfefdf5353db5ccbe36fd21812fec6918bcd4 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Sun, 23 Nov 2025 07:37:04 +1030
Subject: [PATCH 15/41] Test custom sequence's `ExceptionGroup` repr

---
 Lib/test/test_exception_group.py | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index f49f7b27239989..52f1a04d3a996c 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -1,4 +1,4 @@
-import collections.abc
+import collections
 import types
 import unittest
 from test.support import skip_emscripten_stack_overflow, skip_wasi_stack_overflow, exceeds_recursion_limit
@@ -212,9 +212,19 @@ class MyEG(ExceptionGroup):
         excs = (ValueError(1), KeyboardInterrupt(2))
         eg = BaseExceptionGroup('test', excs)
 
-        # Ensure that other, immutable, sequences still work fine.
+        # Ensure that immutable sequences still work fine.
         self.assertEqual(repr(eg), "BaseExceptionGroup('test', (ValueError(1), KeyboardInterrupt(2)))")
 
+        # Test non-standard custom sequences.
+        excs = collections.deque([ValueError(1), TypeError(2)])
+        eg = ExceptionGroup('test', excs)
+
+        self.assertEqual(repr(eg), "ExceptionGroup('test', (ValueError(1), TypeError(2)))")
+        excs.clear()
+
+        # Ensure that clearing the exceptions sequence doesn't change the repr.
+        self.assertEqual(repr(eg), "ExceptionGroup('test', (ValueError(1), TypeError(2)))")
+
 
 def create_simple_eg():
     excs = []

From 2fca592a09b2f6cddb10050d70e83b48a13251ff Mon Sep 17 00:00:00 2001
From: dr-carlos <77367421+dr-carlos@users.noreply.github.com>
Date: Sun, 23 Nov 2025 07:46:26 +1030
Subject: [PATCH 16/41] Update code style in `exceptions.c`
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Objects/exceptions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index a9a053dc350699..d40b2aebdc1126 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1075,7 +1075,8 @@ BaseExceptionGroup_repr(PyObject *op)
     PyObject* excs_orig = PyTuple_GET_ITEM(self->args, 1);
     if (PyList_Check(excs_orig)) {
         excs_orig = PySequence_List(self->excs);
-    } else {
+    }
+    else {
         excs_orig = Py_NewRef(self->excs);
     }
 

From 4885a6b17a2ba15a9c4c8e1621397125ed73f3c3 Mon Sep 17 00:00:00 2001
From: dr-carlos <77367421+dr-carlos@users.noreply.github.com>
Date: Sun, 23 Nov 2025 07:49:56 +1030
Subject: [PATCH 17/41] Update code style in `exceptions.c`
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Objects/exceptions.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index d40b2aebdc1126..273386d6c2fb23 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1082,8 +1082,7 @@ BaseExceptionGroup_repr(PyObject *op)
 
     const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
-        "%s(%R, %R)", name,
-        self->msg, excs_orig);
+        "%T(%R, %R)", self, self->msg, excs_orig);
 
     Py_DECREF(excs_orig);
     return repr;

From 480139929914e5a810067ecb752999495d46bcbc Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Mon, 24 Nov 2025 07:27:26 +1030
Subject: [PATCH 18/41] Remove unused `name` variable with new `%Y` format

---
 Objects/exceptions.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 273386d6c2fb23..a7264b40c1bfc6 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1080,7 +1080,6 @@ BaseExceptionGroup_repr(PyObject *op)
         excs_orig = Py_NewRef(self->excs);
     }
 
-    const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
         "%T(%R, %R)", self, self->msg, excs_orig);
 

From 1bcddeb933d2515c9aaef70a80964ebbb0102a79 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Mon, 24 Nov 2025 09:13:37 +1030
Subject: [PATCH 19/41] Revert "Remove unused `name` variable with new `%Y`
 format"

This reverts commit 480139929914e5a810067ecb752999495d46bcbc.
---
 Objects/exceptions.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index a7264b40c1bfc6..273386d6c2fb23 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1080,6 +1080,7 @@ BaseExceptionGroup_repr(PyObject *op)
         excs_orig = Py_NewRef(self->excs);
     }
 
+    const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
         "%T(%R, %R)", self, self->msg, excs_orig);
 

From ccef7c55442c0c48e01d9d214804058fe1e3fcce Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Mon, 24 Nov 2025 09:13:52 +1030
Subject: [PATCH 20/41] Revert "Update code style in `exceptions.c`"

This reverts commit 4885a6b17a2ba15a9c4c8e1621397125ed73f3c3.
---
 Objects/exceptions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 273386d6c2fb23..d40b2aebdc1126 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1082,7 +1082,8 @@ BaseExceptionGroup_repr(PyObject *op)
 
     const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
-        "%T(%R, %R)", self, self->msg, excs_orig);
+        "%s(%R, %R)", name,
+        self->msg, excs_orig);
 
     Py_DECREF(excs_orig);
     return repr;

From 9ca573ecda58c0b25fab399a70402f4b660b246b Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Tue, 25 Nov 2025 13:45:07 +1030
Subject: [PATCH 21/41] Save repr of non-standard sequences in
 `BaseExceptionGroup` constructor

---
 Include/cpython/pyerrors.h |  1 +
 Objects/exceptions.c       | 46 ++++++++++++++++++++++++++++----------
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/Include/cpython/pyerrors.h b/Include/cpython/pyerrors.h
index 6b63d304b0d929..be2e3b641c25cb 100644
--- a/Include/cpython/pyerrors.h
+++ b/Include/cpython/pyerrors.h
@@ -18,6 +18,7 @@ typedef struct {
     PyException_HEAD
     PyObject *msg;
     PyObject *excs;
+    PyObject *excs_str;
 } PyBaseExceptionGroupObject;
 
 typedef struct {
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index d40b2aebdc1126..5e7c0f1a22cf2c 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -890,6 +890,7 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
     PyObject *message = NULL;
     PyObject *exceptions = NULL;
+    PyObject *exceptions_str = NULL;
 
     if (!PyArg_ParseTuple(args,
                           "UO:BaseExceptionGroup.__new__",
@@ -905,6 +906,11 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
+    /* Save initial exceptions sequence as a string incase sequence is mutated */
+    if (!PyList_Check(exceptions) && !PyTuple_Check(exceptions)) {
+        exceptions_str = PyObject_Repr(exceptions);
+    }
+
     exceptions = PySequence_Tuple(exceptions);
     if (!exceptions) {
         return NULL;
@@ -988,9 +994,11 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
     self->msg = Py_NewRef(message);
     self->excs = exceptions;
+    self->excs_str = exceptions_str;
     return (PyObject*)self;
 error:
     Py_DECREF(exceptions);
+    Py_XDECREF(exceptions_str);
     return NULL;
 }
 
@@ -1029,6 +1037,7 @@ BaseExceptionGroup_clear(PyObject *op)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     Py_CLEAR(self->msg);
     Py_CLEAR(self->excs);
+    Py_CLEAR(self->excs_str);
     return BaseException_clear(op);
 }
 
@@ -1046,6 +1055,7 @@ BaseExceptionGroup_traverse(PyObject *op, visitproc visit, void *arg)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     Py_VISIT(self->msg);
     Py_VISIT(self->excs);
+    Py_VISIT(self->excs_str);
     return BaseException_traverse(op, visit, arg);
 }
 
@@ -1068,24 +1078,34 @@ BaseExceptionGroup_repr(PyObject *op)
 {
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     assert(self->msg);
-    assert(self->excs);
 
-    /* Use the actual exceptions tuple for accuracy, but make it look like the
-     * original exception sequence, if possible, for backwards compatibility. */
-    PyObject* excs_orig = PyTuple_GET_ITEM(self->args, 1);
-    if (PyList_Check(excs_orig)) {
-        excs_orig = PySequence_List(self->excs);
-    }
-    else {
-        excs_orig = Py_NewRef(self->excs);
+    PyObject *exceptions_str = Py_XNewRef(self->excs_str);
+
+    /* If the initial exceptions string was not saved in the constructor. */
+    if (!exceptions_str) {
+        assert(self->excs);
+
+        /* Older versions of this code delegated to BaseException's repr, inserting
+         * the current value of self.args[1]. However, mutating that sequence makes
+         * the repr appear as if the ExceptionGroup itself has changed, which it hasn't.
+         * So we use the actual exceptions tuple for accuracy, but make it look like the
+         * original exception sequence if possible, for backwards compatibility. */
+        if (PyList_Check(PyTuple_GET_ITEM(self->args, 1))) {
+            PyObject *exceptions_list = PySequence_List(self->excs);
+            exceptions_str = PyObject_Repr(exceptions_list);
+            Py_DECREF(exceptions_list);
+        }
+        else {
+            exceptions_str = PyObject_Repr(self->excs);
+        }
     }
 
     const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
-        "%s(%R, %R)", name,
-        self->msg, excs_orig);
+        "%s(%R, %U)", name,
+        self->msg, exceptions_str);
 
-    Py_DECREF(excs_orig);
+    Py_DECREF(exceptions_str);
     return repr;
 }
 
@@ -1708,6 +1728,8 @@ static PyMemberDef BaseExceptionGroup_members[] = {
         PyDoc_STR("exception message")},
     {"exceptions", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs), Py_READONLY,
         PyDoc_STR("nested exceptions")},
+    {"_exceptions_str", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs_str), Py_READONLY,
+        PyDoc_STR("private string representation of initial exceptions sequence")},
     {NULL}  /* Sentinel */
 };
 

From 9531fe90f8f5a234b54ed6c4e2f73a15dc448f88 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Tue, 25 Nov 2025 13:46:54 +1030
Subject: [PATCH 22/41] Update tests for non-standard exceptions sequence in
 `ExceptionGroup`

---
 Lib/test/test_exception_group.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index 52f1a04d3a996c..ecc58e3b7e6e2f 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -219,11 +219,11 @@ class MyEG(ExceptionGroup):
         excs = collections.deque([ValueError(1), TypeError(2)])
         eg = ExceptionGroup('test', excs)
 
-        self.assertEqual(repr(eg), "ExceptionGroup('test', (ValueError(1), TypeError(2)))")
+        self.assertEqual(repr(eg), f"ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
         excs.clear()
 
         # Ensure that clearing the exceptions sequence doesn't change the repr.
-        self.assertEqual(repr(eg), "ExceptionGroup('test', (ValueError(1), TypeError(2)))")
+        self.assertEqual(repr(eg), "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
 
 
 def create_simple_eg():

From 1da923874152439dc51727e29e9921fbccd92173 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 26 Nov 2025 08:28:13 +1030
Subject: [PATCH 23/41] Document implementation details for `ExceptionGroup`
 exception sequence

---
 Doc/library/exceptions.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst
index 16d42c010f6df0..d9b61a0732de8d 100644
--- a/Doc/library/exceptions.rst
+++ b/Doc/library/exceptions.rst
@@ -978,6 +978,12 @@ their subgroups based on the types of the contained exceptions.
    raises a :exc:`TypeError` if any contained exception is not an
    :exc:`Exception` subclass.
 
+   .. impl-detail::
+
+      The ``excs`` parameter may be any sequence, but lists and tuples are
+      specifically processed more efficiently here. For optimum performance,
+      pass a tuple as ``excs``.
+
    .. attribute:: message
 
        The ``msg`` argument to the constructor. This is a read-only attribute.

From fcaf3148e07477535bdf4e64a868651f2c655076 Mon Sep 17 00:00:00 2001
From: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
Date: Wed, 26 Nov 2025 10:22:09 +0000
Subject: [PATCH 24/41] Update
 Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst

---
 .../2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst              | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
index 17848e65bac76c..da96d27598ac43 100644
--- a/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
@@ -1,2 +1,2 @@
 Ensure the repr for :exc:`ExceptionGroup` and :exc:`BaseExceptionGroup` does
-not change when its original exception list is mutated.
+not change when the exception sequence that was original passed in to its constructor is subsequently mutated.

From d9625813a0213bf248bde58011071a01efda36cf Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 26 Nov 2025 22:04:56 +1030
Subject: [PATCH 25/41] Reword 'optimum' to 'optimal' in `exceptions.rst`

---
 Doc/library/exceptions.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst
index d9b61a0732de8d..b5e3a84b4556dd 100644
--- a/Doc/library/exceptions.rst
+++ b/Doc/library/exceptions.rst
@@ -981,7 +981,7 @@ their subgroups based on the types of the contained exceptions.
    .. impl-detail::
 
       The ``excs`` parameter may be any sequence, but lists and tuples are
-      specifically processed more efficiently here. For optimum performance,
+      specifically processed more efficiently here. For optimal performance,
       pass a tuple as ``excs``.
 
    .. attribute:: message

From ce39eec182ff336b85c94380ccb90a6d3cc4f542 Mon Sep 17 00:00:00 2001
From: dr-carlos <77367421+dr-carlos@users.noreply.github.com>
Date: Wed, 26 Nov 2025 22:05:43 +1030
Subject: [PATCH 26/41] Update NEWS Entry
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 .../2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst              | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
index da96d27598ac43..08420fd5f4d18a 100644
--- a/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-19-16-40-24.gh-issue-141732.PTetqp.rst
@@ -1,2 +1,2 @@
-Ensure the repr for :exc:`ExceptionGroup` and :exc:`BaseExceptionGroup` does
+Ensure the :meth:`~object.__repr__` for :exc:`ExceptionGroup` and :exc:`BaseExceptionGroup` does
 not change when the exception sequence that was original passed in to its constructor is subsequently mutated.

From 9211d01a4c401ac79d01e98969318973957d84c6 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 26 Nov 2025 22:55:34 +1030
Subject: [PATCH 27/41] Handle error on `__repr__` for exceptions sequence
 passed to `ExceptionGroup()`

---
 Objects/exceptions.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 5e7c0f1a22cf2c..96732d2a6076c5 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -909,6 +909,13 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     /* Save initial exceptions sequence as a string incase sequence is mutated */
     if (!PyList_Check(exceptions) && !PyTuple_Check(exceptions)) {
         exceptions_str = PyObject_Repr(exceptions);
+        if (exceptions_str == NULL) {
+            /* We don't hold a reference to exceptions, so clear it before
+             * attempting a decref in the cleanup.
+             */
+            exceptions = NULL;
+            goto error;
+        }
     }
 
     exceptions = PySequence_Tuple(exceptions);
@@ -997,7 +1004,7 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     self->excs_str = exceptions_str;
     return (PyObject*)self;
 error:
-    Py_DECREF(exceptions);
+    Py_XDECREF(exceptions);
     Py_XDECREF(exceptions_str);
     return NULL;
 }

From 737206ad4209cedf866f3624c03bf16884f68a8b Mon Sep 17 00:00:00 2001
From: dr-carlos <77367421+dr-carlos@users.noreply.github.com>
Date: Wed, 26 Nov 2025 22:57:11 +1030
Subject: [PATCH 28/41] Change grammar in `exceptions.c`
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Objects/exceptions.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 96732d2a6076c5..315343afa47415 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -906,7 +906,7 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
-    /* Save initial exceptions sequence as a string incase sequence is mutated */
+    /* Save initial exceptions sequence as a string in case sequence is mutated */
     if (!PyList_Check(exceptions) && !PyTuple_Check(exceptions)) {
         exceptions_str = PyObject_Repr(exceptions);
         if (exceptions_str == NULL) {

From 8d17ef32a2b8f53f95d7955bbe609d5006abf19f Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 26 Nov 2025 22:59:15 +1030
Subject: [PATCH 29/41] Update comment relating to `Py_XNewRef` in
 `BaseExceptionGroup_repr()`

---
 Objects/exceptions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 315343afa47415..e909731c9a6c91 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1088,7 +1088,8 @@ BaseExceptionGroup_repr(PyObject *op)
 
     PyObject *exceptions_str = Py_XNewRef(self->excs_str);
 
-    /* If the initial exceptions string was not saved in the constructor. */
+    /* If the initial exceptions string was not saved in the constructor,
+     * our call to Py_XNewRef returns NULL and we now format it on-demand. */
     if (!exceptions_str) {
         assert(self->excs);
 

From 383af2fa929f6fbf2634484114407ec98af8a5ae Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Wed, 26 Nov 2025 23:06:18 +1030
Subject: [PATCH 30/41] Handle `PySequence_List()` and `PyObject_Repr()` errors
 in `BaseException_repr()`

---
 Objects/exceptions.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index e909731c9a6c91..4a90eede8e958c 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1100,6 +1100,10 @@ BaseExceptionGroup_repr(PyObject *op)
          * original exception sequence if possible, for backwards compatibility. */
         if (PyList_Check(PyTuple_GET_ITEM(self->args, 1))) {
             PyObject *exceptions_list = PySequence_List(self->excs);
+            if (!exceptions_list) {
+                goto error;
+            }
+
             exceptions_str = PyObject_Repr(exceptions_list);
             Py_DECREF(exceptions_list);
         }
@@ -1108,6 +1112,10 @@ BaseExceptionGroup_repr(PyObject *op)
         }
     }
 
+    if (!exceptions_str) {
+        goto error;
+    }
+
     const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
         "%s(%R, %U)", name,
@@ -1115,6 +1123,8 @@ BaseExceptionGroup_repr(PyObject *op)
 
     Py_DECREF(exceptions_str);
     return repr;
+error:
+    return NULL;
 }
 
 /*[clinic input]

From 53533403d0f8345ac814326e68e4e5f623b07514 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 07:15:38 +1030
Subject: [PATCH 31/41] Conditionally use `Py_NewRef` in
 `BaseExceptionGroup_repr()`

---
 Objects/exceptions.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 4a90eede8e958c..e9999b56bf4a45 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1086,11 +1086,10 @@ BaseExceptionGroup_repr(PyObject *op)
     PyBaseExceptionGroupObject *self = PyBaseExceptionGroupObject_CAST(op);
     assert(self->msg);
 
-    PyObject *exceptions_str = Py_XNewRef(self->excs_str);
+    PyObject *exceptions_str = NULL;
 
-    /* If the initial exceptions string was not saved in the constructor,
-     * our call to Py_XNewRef returns NULL and we now format it on-demand. */
-    if (!exceptions_str) {
+    /* If the initial exceptions string was not saved in the constructor. */
+    if (!self->excs_str) {
         assert(self->excs);
 
         /* Older versions of this code delegated to BaseException's repr, inserting
@@ -1110,12 +1109,16 @@ BaseExceptionGroup_repr(PyObject *op)
         else {
             exceptions_str = PyObject_Repr(self->excs);
         }
-    }
 
-    if (!exceptions_str) {
-        goto error;
+        if (!exceptions_str) {
+            goto error;
+        }
+    } else {
+        exceptions_str = Py_NewRef(self->excs_str);
     }
 
+    assert(exceptions_str != NULL);
+
     const char *name = _PyType_Name(Py_TYPE(self));
     PyObject *repr = PyUnicode_FromFormat(
         "%s(%R, %U)", name,

From 9997c012f74103067a03c2e0bf275c9e009bd06e Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 07:16:59 +1030
Subject: [PATCH 32/41] Refactor `goto error` into `return NULL` within
 `BaseExceptionGroup_repr()`

---
 Objects/exceptions.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index e9999b56bf4a45..1b7f3574f99139 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1100,7 +1100,7 @@ BaseExceptionGroup_repr(PyObject *op)
         if (PyList_Check(PyTuple_GET_ITEM(self->args, 1))) {
             PyObject *exceptions_list = PySequence_List(self->excs);
             if (!exceptions_list) {
-                goto error;
+                return NULL;
             }
 
             exceptions_str = PyObject_Repr(exceptions_list);
@@ -1111,7 +1111,7 @@ BaseExceptionGroup_repr(PyObject *op)
         }
 
         if (!exceptions_str) {
-            goto error;
+            return NULL;
         }
     } else {
         exceptions_str = Py_NewRef(self->excs_str);
@@ -1126,8 +1126,6 @@ BaseExceptionGroup_repr(PyObject *op)
 
     Py_DECREF(exceptions_str);
     return repr;
-error:
-    return NULL;
 }
 
 /*[clinic input]

From 3cd38db973ebf9cdb20d24af86db08c3b090f865 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 08:50:24 +1030
Subject: [PATCH 33/41] Test custom sequences which raise errors in the
 `ExceptionGroup()` constructor

---
 Lib/test/test_exception_group.py | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index ecc58e3b7e6e2f..ae84fceca7a1eb 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -225,6 +225,31 @@ class MyEG(ExceptionGroup):
         # Ensure that clearing the exceptions sequence doesn't change the repr.
         self.assertEqual(repr(eg), "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
 
+    def test_repr_raises(self):
+        class MySeq(collections.abc.Sequence):
+            def __init__(self, raises):
+                self.raises = raises
+
+            def __len__(self):
+                return 1
+
+            def __getitem__(self, index):
+                if index == 0:
+                    return ValueError(1)
+                raise IndexError
+
+            def __repr__(self):
+                if self.raises:
+                    raise self.raises
+                return None
+
+        with self.assertRaisesRegex(TypeError, r".*MySeq\.__repr__\(\) must return a str, not NoneType"):
+            ExceptionGroup("test", MySeq(None))
+
+        with self.assertRaises(ValueError):
+            BaseExceptionGroup("test", MySeq(ValueError))
+
+
 
 def create_simple_eg():
     excs = []

From 5feb9700b773495c493dbb2b495dd6799fc630a5 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 08:51:47 +1030
Subject: [PATCH 34/41] Fix formatting of if-else in `exceptions.c`

---
 Objects/exceptions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 1b7f3574f99139..daa5505e427d30 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2914,7 +2914,8 @@ SyntaxError_str(PyObject *op)
         filename = my_basename(self->filename);
         if (filename == NULL)
             return NULL;
-    } else {
+    }
+    else {
         filename = NULL;
     }
     have_lineno = (self->lineno != NULL) && PyLong_CheckExact(self->lineno);

From d7aec516e4c2175fb444af507aecdf4f84ef0261 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 08:52:23 +1030
Subject: [PATCH 35/41] Simplify f-string to normal str in
 `test_exceptions_mutation()`

---
 Lib/test/test_exception_group.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index ae84fceca7a1eb..6f8a84350bc6ce 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -219,7 +219,7 @@ class MyEG(ExceptionGroup):
         excs = collections.deque([ValueError(1), TypeError(2)])
         eg = ExceptionGroup('test', excs)
 
-        self.assertEqual(repr(eg), f"ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
+        self.assertEqual(repr(eg), "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
         excs.clear()
 
         # Ensure that clearing the exceptions sequence doesn't change the repr.

From e21fad064bc263866a5e76f7f19e8da0c3d5d966 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 08:56:27 +1030
Subject: [PATCH 36/41] Remove unnecessary `_exceptions_str` member of
 `ExceptionGroup`

---
 Objects/exceptions.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index daa5505e427d30..22b71c60bf10b0 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1747,8 +1747,6 @@ static PyMemberDef BaseExceptionGroup_members[] = {
         PyDoc_STR("exception message")},
     {"exceptions", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs), Py_READONLY,
         PyDoc_STR("nested exceptions")},
-    {"_exceptions_str", _Py_T_OBJECT, offsetof(PyBaseExceptionGroupObject, excs_str), Py_READONLY,
-        PyDoc_STR("private string representation of initial exceptions sequence")},
     {NULL}  /* Sentinel */
 };
 

From 79094f6e85e7f52d6975b2d36ef01f4228075ac0 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 08:58:05 +1030
Subject: [PATCH 37/41] Fix if-else formatting in `exceptions.c`

---
 Objects/exceptions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 22b71c60bf10b0..3435a11814a0a6 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1113,7 +1113,8 @@ BaseExceptionGroup_repr(PyObject *op)
         if (!exceptions_str) {
             return NULL;
         }
-    } else {
+    }
+    else {
         exceptions_str = Py_NewRef(self->excs_str);
     }
 

From b5fcfa78c9890c9a7b7068b168341f1902ca2a32 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Thu, 27 Nov 2025 09:22:27 +1030
Subject: [PATCH 38/41] Keep lines less than 80 chars

---
 Lib/test/test_exception_group.py | 20 ++++++++++++++++----
 Objects/exceptions.c             |  9 ++++-----
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index 6f8a84350bc6ce..488889cde41437 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -213,17 +213,26 @@ class MyEG(ExceptionGroup):
         eg = BaseExceptionGroup('test', excs)
 
         # Ensure that immutable sequences still work fine.
-        self.assertEqual(repr(eg), "BaseExceptionGroup('test', (ValueError(1), KeyboardInterrupt(2)))")
+        self.assertEqual(
+            repr(eg),
+            "BaseExceptionGroup('test', (ValueError(1), KeyboardInterrupt(2)))"
+        )
 
         # Test non-standard custom sequences.
         excs = collections.deque([ValueError(1), TypeError(2)])
         eg = ExceptionGroup('test', excs)
 
-        self.assertEqual(repr(eg), "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
+        self.assertEqual(
+            repr(eg),
+            "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))"
+        )
         excs.clear()
 
         # Ensure that clearing the exceptions sequence doesn't change the repr.
-        self.assertEqual(repr(eg), "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))")
+        self.assertEqual(
+            repr(eg),
+            "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))"
+        )
 
     def test_repr_raises(self):
         class MySeq(collections.abc.Sequence):
@@ -243,7 +252,10 @@ def __repr__(self):
                     raise self.raises
                 return None
 
-        with self.assertRaisesRegex(TypeError, r".*MySeq\.__repr__\(\) must return a str, not NoneType"):
+        with self.assertRaisesRegex(
+            TypeError,
+            r".*MySeq\.__repr__\(\) must return a str, not NoneType"
+        ):
             ExceptionGroup("test", MySeq(None))
 
         with self.assertRaises(ValueError):
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 3435a11814a0a6..507b1166b87bec 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1092,11 +1092,10 @@ BaseExceptionGroup_repr(PyObject *op)
     if (!self->excs_str) {
         assert(self->excs);
 
-        /* Older versions of this code delegated to BaseException's repr, inserting
-         * the current value of self.args[1]. However, mutating that sequence makes
-         * the repr appear as if the ExceptionGroup itself has changed, which it hasn't.
-         * So we use the actual exceptions tuple for accuracy, but make it look like the
-         * original exception sequence if possible, for backwards compatibility. */
+        /* Older versions delegated to BaseException, inserting the current
+         * value of self.args[1]; but this can be mutable and go out-of-sync
+         * with self.exceptions. Instead, use self.exceptions for accuracy,
+         * making it look like self.args[1] for backwards compatibility. */
         if (PyList_Check(PyTuple_GET_ITEM(self->args, 1))) {
             PyObject *exceptions_list = PySequence_List(self->excs);
             if (!exceptions_list) {

From 57f8bf62984cb86953c05ee7751c0853fe2a838e Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Fri, 28 Nov 2025 08:15:00 +1030
Subject: [PATCH 39/41] Revert "Fix formatting of if-else in `exceptions.c`"

This reverts commit 5feb9700b773495c493dbb2b495dd6799fc630a5.
---
 Objects/exceptions.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 507b1166b87bec..f0af2bbad9dcb1 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2912,8 +2912,7 @@ SyntaxError_str(PyObject *op)
         filename = my_basename(self->filename);
         if (filename == NULL)
             return NULL;
-    }
-    else {
+    } else {
         filename = NULL;
     }
     have_lineno = (self->lineno != NULL) && PyLong_CheckExact(self->lineno);

From 9cba6b64ab0815b727ee1a08ae6ea390117bf5b3 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Fri, 28 Nov 2025 08:16:39 +1030
Subject: [PATCH 40/41] Construct custom sequence outside of `assertRaises`
 context manager in `test_repr_raises()`

---
 Lib/test/test_exception_group.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_exception_group.py b/Lib/test/test_exception_group.py
index 488889cde41437..ace7ec72917934 100644
--- a/Lib/test/test_exception_group.py
+++ b/Lib/test/test_exception_group.py
@@ -252,14 +252,16 @@ def __repr__(self):
                     raise self.raises
                 return None
 
+        seq = MySeq(None)
         with self.assertRaisesRegex(
             TypeError,
             r".*MySeq\.__repr__\(\) must return a str, not NoneType"
         ):
-            ExceptionGroup("test", MySeq(None))
+            ExceptionGroup("test", seq)
 
+        seq = MySeq(ValueError)
         with self.assertRaises(ValueError):
-            BaseExceptionGroup("test", MySeq(ValueError))
+            BaseExceptionGroup("test", seq)
 
 
 

From d61e6b9b3e006834b92a58e27a0ef3767d014704 Mon Sep 17 00:00:00 2001
From: dr-carlos <dr_steven_carlos@outlook.com>
Date: Fri, 28 Nov 2025 08:19:04 +1030
Subject: [PATCH 41/41] Swap order of if-else branches and clarify comment in
 `BaseExceptionGroup_repr()`

---
 Objects/exceptions.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index f0af2bbad9dcb1..9a43057b383d29 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1088,8 +1088,11 @@ BaseExceptionGroup_repr(PyObject *op)
 
     PyObject *exceptions_str = NULL;
 
-    /* If the initial exceptions string was not saved in the constructor. */
-    if (!self->excs_str) {
+    /* Use the saved exceptions string for custom sequences. */
+    if (self->excs_str) {
+        exceptions_str = Py_NewRef(self->excs_str);
+    }
+    else {
         assert(self->excs);
 
         /* Older versions delegated to BaseException, inserting the current
@@ -1113,9 +1116,6 @@ BaseExceptionGroup_repr(PyObject *op)
             return NULL;
         }
     }
-    else {
-        exceptions_str = Py_NewRef(self->excs_str);
-    }
 
     assert(exceptions_str != NULL);