From 7e8b153fef71e464246827bf563923e2991290c6 Mon Sep 17 00:00:00 2001
From: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
Date: Tue, 29 Apr 2025 22:18:06 -0700
Subject: gh-116436: Improve error message when TypeError occurs during dict
 update (#116443)

---
 Lib/test/test_dict.py                              | 25 ++++++++++++++++++++++
 .../2024-03-06-22-33-33.gh-issue-116436.y8Thkt.rst |  1 +
 Objects/dictobject.c                               |  9 ++++----
 3 files changed, 31 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2024-03-06-22-33-33.gh-issue-116436.y8Thkt.rst

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 9485ef2..3104cbc 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -266,6 +266,31 @@ class DictTest(unittest.TestCase):
 
         self.assertRaises(ValueError, {}.update, [(1, 2, 3)])
 
+    def test_update_type_error(self):
+        with self.assertRaises(TypeError) as cm:
+            {}.update([object() for _ in range(3)])
+
+        self.assertEqual(str(cm.exception), "object is not iterable")
+        self.assertEqual(
+            cm.exception.__notes__,
+            ['Cannot convert dictionary update sequence element #0 to a sequence'],
+        )
+
+        def badgen():
+            yield "key"
+            raise TypeError("oops")
+            yield "value"
+
+        with self.assertRaises(TypeError) as cm:
+            dict([badgen() for _ in range(3)])
+
+        self.assertEqual(str(cm.exception), "oops")
+        self.assertEqual(
+            cm.exception.__notes__,
+            ['Cannot convert dictionary update sequence element #0 to a sequence'],
+        )
+
+
     def test_fromkeys(self):
         self.assertEqual(dict.fromkeys('abc'), {'a':None, 'b':None, 'c':None})
         d = {}
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-03-06-22-33-33.gh-issue-116436.y8Thkt.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-03-06-22-33-33.gh-issue-116436.y8Thkt.rst
new file mode 100644
index 0000000..f9c3ab1
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-03-06-22-33-33.gh-issue-116436.y8Thkt.rst
@@ -0,0 +1 @@
+Improve error message when :exc:`TypeError` occurs during :meth:`dict.update`
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 4fdfd63..b6f623b 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -3730,13 +3730,14 @@ merge_from_seq2_lock_held(PyObject *d, PyObject *seq2, int override)
         }
 
         /* Convert item to sequence, and verify length 2. */
-        fast = PySequence_Fast(item, "");
+        fast = PySequence_Fast(item, "object is not iterable");
         if (fast == NULL) {
-            if (PyErr_ExceptionMatches(PyExc_TypeError))
-                PyErr_Format(PyExc_TypeError,
-                    "cannot convert dictionary update "
+            if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+                _PyErr_FormatNote(
+                    "Cannot convert dictionary update "
                     "sequence element #%zd to a sequence",
                     i);
+            }
             goto Fail;
         }
         n = PySequence_Fast_GET_SIZE(fast);
-- 
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