Fixed #25186 -- Improved migration's serialization of builtins on Python 2.

django/db/migrations/writer.py

@@ -472,6 +472,9 @@ class MigrationWriter(object):
                     "For more information, see "
                     "https://docs.djangoproject.com/en/%s/topics/migrations/#serializing-values"
                     % (value.__name__, module_name, get_docs_version()))
+            # Needed on Python 2 only
+            if module_name == '__builtin__':
+                return value.__name__, set()
             return "%s.%s" % (module_name, value.__name__), {"import %s" % module_name}
         # Other iterables
         elif isinstance(value, collections.Iterable):

tests/migrations/test_writer.py

@@ -359,6 +359,11 @@ class WriterTests(SimpleTestCase):
         self.assertSerializedEqual(one_item_tuple)
         self.assertSerializedEqual(many_items_tuple)
 
+    def test_serialize_builtins(self):
+        string, imports = MigrationWriter.serialize(range)
+        self.assertEqual(string, 'range')
+        self.assertEqual(imports, set())
+
     @unittest.skipUnless(six.PY2, "Only applies on Python 2")
     def test_serialize_direct_function_reference(self):
         """