GH-146096: Fix segfault in BaseExceptionGroup repr (GH-146141)

(cherry picked from commit ced6460)

Co-authored-by: Sergey Miryanov <sergey.miryanov@gmail.com>

Author: sergey-miryanov

Lib/test/test_exception_group.py

@@ -236,6 +236,18 @@ class MyEG(ExceptionGroup):
             "ExceptionGroup('test', deque([ValueError(1), TypeError(2)]))"
         )
 
+    def test_repr_small_size_args(self):
+        eg = ExceptionGroup("msg", [ValueError()])
+        eg.args = ()
+        # repr of the ExceptionGroup with empty args should not crash
+        self.assertEqual(repr(eg), "ExceptionGroup('msg', (ValueError(),))")
+
+        eg.args = (1,)
+        # repr of the ExceptionGroup with 1-size args should not crash
+        self.assertEqual(repr(eg), "ExceptionGroup('msg', (ValueError(),))")
+
+
+
     def test_repr_raises(self):
         class MySeq(collections.abc.Sequence):
             def __init__(self, raises):

Misc/NEWS.d/next/Core_and_Builtins/2026-03-19-01-19-34.gh-issue-146096.R9tkJX.rst

@@ -0,0 +1,2 @@
+Fixed segmentation fault when called repr for BaseExceptionGroup with empty
+or 1-size tuple args.

Objects/exceptions.c

@@ -1104,7 +1104,8 @@ BaseExceptionGroup_repr(PyObject *op)
          * 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))) {
+        assert(PyTuple_Check(self->args));
+        if (PyTuple_GET_SIZE(self->args) == 2 && PyList_Check(PyTuple_GET_ITEM(self->args, 1))) {
             PyObject *exceptions_list = PySequence_List(self->excs);
             if (!exceptions_list) {
                 return NULL;