From f73377d57c5272390de63cccc3c292c44689310a Mon Sep 17 00:00:00 2001
From: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
Date: Thu, 17 Jun 2021 17:14:30 +0100
Subject: [PATCH] =?UTF-8?q?bpo-43024:=20improve=20signature=20(in=20help,?=
 =?UTF-8?q?=20etc)=20for=20functions=20taking=20sent=E2=80=A6=20(GH-24331)?=
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…inel defaults
---
 Lib/test/test_traceback.py                       | 16 ++++++++++++++++
 Lib/traceback.py                                 |  5 ++++-
 .../2021-01-25-21-24-55.bpo-43024.vAUrIi.rst     |  1 +
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-01-25-21-24-55.bpo-43024.vAUrIi.rst

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index e9df1ce9c79..78b2851d384 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -4,6 +4,7 @@ from collections import namedtuple
 from io import StringIO
 import linecache
 import sys
+import inspect
 import unittest
 import re
 from test import support
@@ -255,6 +256,21 @@ class TracebackCases(unittest.TestCase):
         self.assertEqual(
             traceback.format_exception_only(None, None), [NONE_EXC_STRING])
 
+    def test_signatures(self):
+        self.assertEqual(
+            str(inspect.signature(traceback.print_exception)),
+            ('(exc, /, value=<implicit>, tb=<implicit>, '
+             'limit=None, file=None, chain=True)'))
+
+        self.assertEqual(
+            str(inspect.signature(traceback.format_exception)),
+            ('(exc, /, value=<implicit>, tb=<implicit>, limit=None, '
+             'chain=True)'))
+
+        self.assertEqual(
+            str(inspect.signature(traceback.format_exception_only)),
+            '(exc, /, value=<implicit>)')
+
 
 class TracebackFormatTests(unittest.TestCase):
 
diff --git a/Lib/traceback.py b/Lib/traceback.py
index e19745df6de..b4c7641adde 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -84,8 +84,11 @@ _context_message = (
     "another exception occurred:\n\n")
 
 
-_sentinel = object()
+class _Sentinel:
+    def __repr__(self):
+        return "<implicit>"
 
+_sentinel = _Sentinel()
 
 def _parse_value_tb(exc, value, tb):
     if (value is _sentinel) != (tb is _sentinel):
diff --git a/Misc/NEWS.d/next/Library/2021-01-25-21-24-55.bpo-43024.vAUrIi.rst b/Misc/NEWS.d/next/Library/2021-01-25-21-24-55.bpo-43024.vAUrIi.rst
new file mode 100644
index 00000000000..56596ce3c2a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-01-25-21-24-55.bpo-43024.vAUrIi.rst
@@ -0,0 +1 @@
+Improve the help signature of :func:`traceback.print_exception`, :func:`traceback.format_exception` and :func:`traceback.format_exception_only`.