bpo-28603: Fix formatting tracebacks for unhashable exceptions (#4014)

2 files changed, 38 insertions, 3 deletions

diff --git a/Lib/idlelib/idle_test/test_run.py b/Lib/idlelib/idle_test/test_run.py
new file mode 100644
index 0000000..d7e627d
--- /dev/null
+++ b/Lib/idlelib/idle_test/test_run.py
@@ -0,0 +1,35 @@
+import unittest
+from unittest import mock
+
+from test.support import captured_stderr
+import idlelib.run as idlerun
+
+
+class RunTest(unittest.TestCase):
+    def test_print_exception_unhashable(self):
+        class UnhashableException(Exception):
+            def __eq__(self, other):
+                return True
+
+        ex1 = UnhashableException('ex1')
+        ex2 = UnhashableException('ex2')
+        try:
+            raise ex2 from ex1
+        except UnhashableException:
+            try:
+                raise ex1
+            except UnhashableException:
+                with captured_stderr() as output:
+                    with mock.patch.object(idlerun,
+                                           'cleanup_traceback') as ct:
+                        ct.side_effect = lambda t, e: t
+                        idlerun.print_exception()
+
+        tb = output.getvalue().strip().splitlines()
+        self.assertEqual(11, len(tb))
+        self.assertIn('UnhashableException: ex2', tb[3])
+        self.assertIn('UnhashableException: ex1', tb[10])
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)
diff --git a/Lib/idlelib/run.py b/Lib/idlelib/run.py
index 39e0c11..6440e67 100644
--- a/Lib/idlelib/run.py
+++ b/Lib/idlelib/run.py
@@ -203,16 +203,16 @@ def print_exception():
     seen = set()
 
     def print_exc(typ, exc, tb):
-        seen.add(exc)
+        seen.add(id(exc))
         context = exc.__context__
         cause = exc.__cause__
-        if cause is not None and cause not in seen:
+        if cause is not None and id(cause) not in seen:
             print_exc(type(cause), cause, cause.__traceback__)
             print("\nThe above exception was the direct cause "
                   "of the following exception:\n", file=efile)
         elif (context is not None and
               not exc.__suppress_context__ and
-              context not in seen):
+              id(context) not in seen):
             print_exc(type(context), context, context.__traceback__)
             print("\nDuring handling of the above exception, "
                   "another exception occurred:\n", file=efile)