gh-130821: Add type info to error message in Modules/_abc.c

When an item yielded by a class namespace's items() is not iterable
during abstract-method computation, include the type of the offending
item in the raised TypeError, matching the type-information convention
established in gh-130835.

This targets the same _abc.c hunk that gh-144737 (now stale) proposed,
using PyErr_ExceptionMatches to only replace the message on a genuine
TypeError instead of passing NULL through PySequence_Fast, which risks
a NULL PyErr_SetString call if that path is ever reached with a
different underlying error.

Author: JMak-Security

Misc/NEWS.d/next/Core_and_Builtins/2026-08-20-15-00-00.gh-issue-130821.abc-item-type.rst

@@ -0,0 +1,3 @@
+Include the type name in the :exc:`TypeError` raised when an item yielded by
+``items()`` is not iterable during abstract method computation in
+:mod:`abc`. Patch by Jason Mak.

Modules/_abc.c

@@ -383,10 +383,17 @@ compute_abstract_methods(PyObject *self)
     }
     assert(PyList_Check(items));
     for (Py_ssize_t pos = 0; pos < PyList_GET_SIZE(items); pos++) {
+        PyObject *item = PyList_GET_ITEM(items, pos);
         PyObject *it = PySequence_Fast(
-                PyList_GET_ITEM(items, pos),
+                item,
                 "items() returned non-iterable");
         if (!it) {
+            if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+                PyErr_Format(PyExc_TypeError,
+                             "items() must yield iterable (key, value) "
+                             "pairs, not %T",
+                             item);
+            }
             goto error;
         }
         if (PySequence_Fast_GET_SIZE(it) != 2) {