Issue #18776: atexit callbacks now display their full traceback when they raise an exception.

Lib/test/test_atexit.py

@@ -74,6 +74,25 @@ class TestCase(unittest.TestCase):
         self.assertRaises(ZeroDivisionError, atexit._run_exitfuncs)
         self.assertIn("ZeroDivisionError", self.stream.getvalue())
 
+    def test_print_tracebacks(self):
+        # Issue #18776: the tracebacks should be printed when errors occur.
+        def f():
+            1/0  # one
+        def g():
+            1/0  # two
+        def h():
+            1/0  # three
+        atexit.register(f)
+        atexit.register(g)
+        atexit.register(h)
+
+        self.assertRaises(ZeroDivisionError, atexit._run_exitfuncs)
+        stderr = self.stream.getvalue()
+        self.assertEqual(stderr.count("ZeroDivisionError"), 3)
+        self.assertIn("# one", stderr)
+        self.assertIn("# two", stderr)
+        self.assertIn("# three", stderr)
+
     def test_stress(self):
         a = [0]
         def inc():