gh-94510: Raise on re-entrant calls to sys.setprofile and sys.settrace (GH-94511)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Lib/test/test_sys_settrace.py

@@ -2,6 +2,7 @@
 
 from test import support
 import unittest
+from unittest.mock import MagicMock
 import sys
 import difflib
 import gc
@@ -2684,5 +2685,43 @@ class TestExtendedArgs(unittest.TestCase):
         self.assertEqual(counts, {'call': 1, 'line': 2000, 'return': 1})
 
 
+class TestEdgeCases(unittest.TestCase):
+
+    def setUp(self):
+        self.addCleanup(sys.settrace, sys.gettrace())
+        sys.settrace(None)
+
+    def test_reentrancy(self):
+        def foo(*args):
+            ...
+
+        def bar(*args):
+            ...
+
+        class A:
+            def __call__(self, *args):
+                pass
+
+            def __del__(self):
+                sys.settrace(bar)
+
+        sys.settrace(A())
+        with support.catch_unraisable_exception() as cm:
+            sys.settrace(foo)
+            self.assertEqual(cm.unraisable.object, A.__del__)
+            self.assertIsInstance(cm.unraisable.exc_value, RuntimeError)
+
+        self.assertEqual(sys.gettrace(), foo)
+
+
+    def test_same_object(self):
+        def foo(*args):
+            ...
+
+        sys.settrace(foo)
+        del foo
+        sys.settrace(sys.gettrace())
+
+
 if __name__ == "__main__":
     unittest.main()