PR feedback

Author: csm10495

Lib/test/list_tests.py

@@ -228,6 +228,30 @@ def infinite_gen():
             a[::-2] = infinite_gen()
         self.assertEqual(a, self.type2test(range(6)))
 
+        # Explicit start and stop with infinite iterator
+        a = self.type2test(range(10))
+        with self.assertRaises(ValueError):
+            a[1:8:2] = infinite_gen()
+        self.assertEqual(a, self.type2test(range(10)))
+
+        # Explicit start only
+        a = self.type2test(range(10))
+        with self.assertRaises(ValueError):
+            a[2::3] = infinite_gen()
+        self.assertEqual(a, self.type2test(range(10)))
+
+        # Explicit stop only
+        a = self.type2test(range(10))
+        with self.assertRaises(ValueError):
+            a[:7:2] = infinite_gen()
+        self.assertEqual(a, self.type2test(range(10)))
+
+        # Negative step with explicit start and stop
+        a = self.type2test(range(10))
+        with self.assertRaises(ValueError):
+            a[8:1:-2] = infinite_gen()
+        self.assertEqual(a, self.type2test(range(10)))
+
     def test_extended_slice_assign_iterator(self):
         # Assigning a finite iterator with the correct length to an
         # extended slice should work.

Objects/listobject.c

@@ -3845,9 +3845,11 @@ list_ass_subscript_lock_held(PyObject *_self, PyObject *item, PyObject *value)
                 PyObject *it = PyObject_GetIter(value);
                 if (it == NULL) {
                     if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+                        PyObject *exc = PyErr_GetRaisedException();
                         PyErr_SetString(PyExc_TypeError,
                                         "must assign iterable "
                                         "to extended slice");
+                        _PyErr_ChainExceptions1(exc);
                     }
                     return -1;
                 }