diff -r ebf189626763 Python/ceval.c
--- a/Python/ceval.c	Mon Sep 19 22:20:19 2016 -0700
+++ b/Python/ceval.c	Wed Sep 21 00:54:20 2016 +0800
@@ -5200,9 +5200,9 @@
     _Py_IDENTIFIER(__all__);
     _Py_IDENTIFIER(__dict__);
     PyObject *all = _PyObject_GetAttrId(v, &PyId___all__);
-    PyObject *dict, *name, *value;
-    int skip_leading_underscores = 0;
-    int pos, err;
+    PyObject *dict, *name, *value, **items;
+    Py_ssize_t i, size;
+    int skip_leading_underscores = 0, err;
 
     if (all == NULL) {
         if (!PyErr_ExceptionMatches(PyExc_AttributeError))
@@ -5221,34 +5221,35 @@
         if (all == NULL)
             return -1;
         skip_leading_underscores = 1;
+    } else if (!(PyList_CheckExact(all) || PyTuple_CheckExact(all))){
+        PyObject *seq = PySequence_Fast(all, "__all__ is not iterable");
+        if (seq == NULL) {
+            return -1;
+        }
+        Py_SETREF(all, seq);
     }
 
-    for (pos = 0, err = 0; ; pos++) {
-        name = PySequence_GetItem(all, pos);
-        if (name == NULL) {
-            if (!PyErr_ExceptionMatches(PyExc_IndexError))
-                err = -1;
-            else
-                PyErr_Clear();
-            break;
-        }
+    size = PySequence_Fast_GET_SIZE(all);
+    items = PySequence_Fast_ITEMS(all);
+    for (i = 0, err = 0; i < size; i++) {
+        name = items[i];                  // borrowed
         if (skip_leading_underscores &&
             PyUnicode_Check(name) &&
             PyUnicode_READY(name) != -1 &&
             PyUnicode_READ_CHAR(name, 0) == '_')
         {
-            Py_DECREF(name);
             continue;
         }
         value = PyObject_GetAttr(v, name);
-        if (value == NULL)
+        if (value == NULL) {
             err = -1;
-        else if (PyDict_CheckExact(locals))
+            break;
+        }
+        if (PyDict_Check(locals))
             err = PyDict_SetItem(locals, name, value);
         else
             err = PyObject_SetItem(locals, name, value);
-        Py_DECREF(name);
-        Py_XDECREF(value);
+        Py_DECREF(value);
         if (err != 0)
             break;
     }