[2.7] bpo-35441: Remove dead and buggy code related to PyList_SetItem(). (GH-11033) (GH-11234)

In _localemodule.c and selectmodule.c, remove dead code that would
cause double decrefs if run.

In addition, replace PyList_SetItem() with PyList_SET_ITEM() in cases
where a new list is populated and there is no possibility of an error.

In addition, check if the list changed size in the loop in array_array_fromlist().
(cherry picked from commit 99d56b53560b3867844472ae381fb3f858760621)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/Modules/arraymodule.c b/Modules/arraymodule.c
index 5bd3a42..8d4eb09 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -1344,7 +1344,7 @@ array_fromlist(arrayobject *self, PyObject *list)
         Py_SIZE(self) += n;
         self->allocated = Py_SIZE(self);
         for (i = 0; i < n; i++) {
-            PyObject *v = PyList_GetItem(list, i);
+            PyObject *v = PyList_GET_ITEM(list, i);
             if ((*self->ob_descr->setitem)(self,
                             Py_SIZE(self) - n + i, v) != 0) {
                 Py_SIZE(self) -= n;
@@ -1357,6 +1357,19 @@ array_fromlist(arrayobject *self, PyObject *list)
                 self->allocated = Py_SIZE(self);
                 return NULL;
             }
+            if (n != PyList_GET_SIZE(list)) {
+                PyErr_SetString(PyExc_RuntimeError,
+                                "list changed size during iteration");
+                Py_SIZE(self) -= n;
+                if (itemsize && (Py_SIZE(self) > PY_SSIZE_T_MAX / itemsize)) {
+                    return PyErr_NoMemory();
+                }
+                PyMem_RESIZE(item, char,
+                                  Py_SIZE(self) * itemsize);
+                self->ob_item = item;
+                self->allocated = Py_SIZE(self);
+                return NULL;
+            }
         }
     }
     Py_INCREF(Py_None);
@@ -1383,7 +1396,7 @@ array_tolist(arrayobject *self, PyObject *unused)
             Py_DECREF(list);
             return NULL;
         }
-        PyList_SetItem(list, i, v);
+        PyList_SET_ITEM(list, i, v);
     }
     return list;
 }