From 40b92f1cc06f9aaba813ae38266f424e0969b089 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Fri, 4 Dec 2020 12:57:31 -0800
Subject: [PATCH] [3.9] bpo-42482: remove reference to exc_traceback from
 TracebackException (GH-23531) (GH-23578)

(cherry picked from commit 427613f005f0f412d12f0d775d2b609bae0ae1ad)


Co-authored-by: Irit Katriel <iritkatriel@yahoo.com>
---
 Lib/test/test_traceback.py                    | 22 +++++++++++++++++++
 Lib/traceback.py                              |  5 ++---
 .../2020-11-27-16-46-58.bpo-42482.EJC3sd.rst  |  1 +
 3 files changed, 25 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-11-27-16-46-58.bpo-42482.EJC3sd.rst

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index d564f3040ea..8549ba2b75a 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -1103,6 +1103,18 @@ class TestTracebackException(unittest.TestCase):
         self.assertEqual(exc_info[0], exc.exc_type)
         self.assertEqual(str(exc_info[1]), str(exc))
 
+    def test_no_refs_to_exception_and_traceback_objects(self):
+        try:
+            1/0
+        except Exception:
+            exc_info = sys.exc_info()
+
+        refcnt1 = sys.getrefcount(exc_info[1])
+        refcnt2 = sys.getrefcount(exc_info[2])
+        exc = traceback.TracebackException(*exc_info)
+        self.assertEqual(sys.getrefcount(exc_info[1]), refcnt1)
+        self.assertEqual(sys.getrefcount(exc_info[2]), refcnt2)
+
     def test_comparison_basic(self):
         try:
             1/0
@@ -1152,6 +1164,16 @@ class TestTracebackException(unittest.TestCase):
         exc7 = traceback.TracebackException(*exc_info, limit=-2, capture_locals=True)
         self.assertNotEqual(exc6, exc7)
 
+    def test_comparison_equivalent_exceptions_are_equal(self):
+        excs = []
+        for _ in range(2):
+            try:
+                1/0
+            except:
+                excs.append(traceback.TracebackException(*sys.exc_info()))
+        self.assertEqual(excs[0], excs[1])
+        self.assertEqual(list(excs[0].format()), list(excs[1].format()))
+
     def test_unhashable(self):
         class UnhashableException(Exception):
             def __eq__(self, other):
diff --git a/Lib/traceback.py b/Lib/traceback.py
index a19e38718b1..fb34de94893 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -500,7 +500,6 @@ class TracebackException:
                 _seen=_seen)
         else:
             context = None
-        self.exc_traceback = exc_traceback
         self.__cause__ = cause
         self.__context__ = context
         self.__suppress_context__ = \
@@ -617,7 +616,7 @@ class TracebackException:
                 not self.__suppress_context__):
                 yield from self.__context__.format(chain=chain)
                 yield _context_message
-        if self.exc_traceback is not None:
+        if self.stack:
             yield 'Traceback (most recent call last):\n'
-        yield from self.stack.format()
+            yield from self.stack.format()
         yield from self.format_exception_only()
diff --git a/Misc/NEWS.d/next/Library/2020-11-27-16-46-58.bpo-42482.EJC3sd.rst b/Misc/NEWS.d/next/Library/2020-11-27-16-46-58.bpo-42482.EJC3sd.rst
new file mode 100644
index 00000000000..79afa654f35
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-11-27-16-46-58.bpo-42482.EJC3sd.rst
@@ -0,0 +1 @@
+:class:`~traceback.TracebackException` no longer holds a reference to the exception's traceback object. Consequently, instances of TracebackException for equivalent but non-equal exceptions now compare as equal.
\ No newline at end of file