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

4 files changed, 87 insertions, 6 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)
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index e483353..bffc03e 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -443,6 +443,33 @@ class TracebackFormatTests(unittest.TestCase):
             '    return traceback.format_stack()\n' % (__file__, lineno+1),
         ])
 
+    @cpython_only
+    def test_unhashable(self):
+        from _testcapi import exception_print
+
+        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:
+                exc_type, exc_val, exc_tb = sys.exc_info()
+
+        with captured_output("stderr") as stderr_f:
+            exception_print(exc_val)
+
+        tb = stderr_f.getvalue().strip().splitlines()
+        self.assertEqual(11, len(tb))
+        self.assertEqual(context_message.strip(), tb[5])
+        self.assertIn('UnhashableException: ex2', tb[3])
+        self.assertIn('UnhashableException: ex1', tb[10])
+
 
 cause_message = (
     "\nThe above exception was the direct cause "
@@ -994,6 +1021,25 @@ class TestTracebackException(unittest.TestCase):
         self.assertEqual(exc_info[0], exc.exc_type)
         self.assertEqual(str(exc_info[1]), str(exc))
 
+    def test_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:
+                exc_info = sys.exc_info()
+        exc = traceback.TracebackException(*exc_info)
+        formatted = list(exc.format())
+        self.assertIn('UnhashableException: ex2\n', formatted[2])
+        self.assertIn('UnhashableException: ex1\n', formatted[6])
+
     def test_limit(self):
         def recurse(n):
             if n:
diff --git a/Lib/traceback.py b/Lib/traceback.py
index fb3bce1..ee8c739 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -458,11 +458,11 @@ class TracebackException:
         # Handle loops in __cause__ or __context__.
         if _seen is None:
             _seen = set()
-        _seen.add(exc_value)
+        _seen.add(id(exc_value))
         # Gracefully handle (the way Python 2.4 and earlier did) the case of
         # being called with no type or value (None, None, None).
         if (exc_value and exc_value.__cause__ is not None
-            and exc_value.__cause__ not in _seen):
+            and id(exc_value.__cause__) not in _seen):
             cause = TracebackException(
                 type(exc_value.__cause__),
                 exc_value.__cause__,
@@ -474,7 +474,7 @@ class TracebackException:
         else:
             cause = None
         if (exc_value and exc_value.__context__ is not None
-            and exc_value.__context__ not in _seen):
+            and id(exc_value.__context__) not in _seen):
             context = TracebackException(
                 type(exc_value.__context__),
                 exc_value.__context__,