changeset:   102749:c3498187f998
user:        Berker Peksag <berker.peksag@gmail.com>
date:        Fri Aug 19 11:04:07 2016 +0300
files:       Doc/library/functions.rst Lib/test/test_types.py Misc/NEWS Objects/typeobject.c
description:
Issue #27157: Make only type() itself accept the one-argument form

Patch by Eryk Sun and Emanuel Barry.


diff -r dd0f1fa809c5 -r c3498187f998 Doc/library/functions.rst
--- a/Doc/library/functions.rst	Thu Aug 18 21:45:12 2016 -0400
+++ b/Doc/library/functions.rst	Fri Aug 19 11:04:07 2016 +0300
@@ -1463,6 +1463,9 @@
 
    See also :ref:`bltin-type-objects`.
 
+   .. versionchanged:: 3.6
+      Subclasses of :class:`type` which don't override ``type.__new__`` may no
+      longer use the one-argument form to get the type of an object.
 
 .. function:: vars([object])
 
diff -r dd0f1fa809c5 -r c3498187f998 Lib/test/test_types.py
--- a/Lib/test/test_types.py	Thu Aug 18 21:45:12 2016 -0400
+++ b/Lib/test/test_types.py	Fri Aug 19 11:04:07 2016 +0300
@@ -1000,6 +1000,24 @@
         with self.assertRaises(TypeError):
             X = types.new_class("X", (int(), C))
 
+    def test_one_argument_type(self):
+        expected_message = 'type.__new__() takes exactly 3 arguments (1 given)'
+
+        # Only type itself can use the one-argument form (#27157)
+        self.assertIs(type(5), int)
+
+        class M(type):
+            pass
+        with self.assertRaises(TypeError) as cm:
+            M(5)
+        self.assertEqual(str(cm.exception), expected_message)
+
+        class N(type, metaclass=M):
+            pass
+        with self.assertRaises(TypeError) as cm:
+            N(5)
+        self.assertEqual(str(cm.exception), expected_message)
+
 
 class SimpleNamespaceTests(unittest.TestCase):
 
diff -r dd0f1fa809c5 -r c3498187f998 Misc/NEWS
--- a/Misc/NEWS	Thu Aug 18 21:45:12 2016 -0400
+++ b/Misc/NEWS	Fri Aug 19 11:04:07 2016 +0300
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #27157: Make only type() itself accept the one-argument form.
+  Patch by Eryk Sun and Emanuel Barry.
+
 - Issue #27558: Fix a SystemError in the implementation of "raise" statement.
   In a brand new thread, raise a RuntimeError since there is no active
   exception to reraise. Patch written by Xiang Zhang.
diff -r dd0f1fa809c5 -r c3498187f998 Objects/typeobject.c
--- a/Objects/typeobject.c	Thu Aug 18 21:45:12 2016 -0400
+++ b/Objects/typeobject.c	Fri Aug 19 11:04:07 2016 +0300
@@ -2287,11 +2287,13 @@
     assert(kwds == NULL || PyDict_Check(kwds));
 
     /* Special case: type(x) should return x->ob_type */
-    {
+    /* We only want type itself to accept the one-argument form (#27157)
+       Note: We don't call PyType_CheckExact as that also allows subclasses */
+    if (metatype == &PyType_Type) {
         const Py_ssize_t nargs = PyTuple_GET_SIZE(args);
         const Py_ssize_t nkwds = kwds == NULL ? 0 : PyDict_Size(kwds);
 
-        if (PyType_CheckExact(metatype) && nargs == 1 && nkwds == 0) {
+        if (nargs == 1 && nkwds == 0) {
             PyObject *x = PyTuple_GET_ITEM(args, 0);
             Py_INCREF(Py_TYPE(x));
             return (PyObject *) Py_TYPE(x);
@@ -2308,8 +2310,8 @@
     }
 
     /* Check arguments: (name, bases, dict) */
-    if (!PyArg_ParseTuple(args, "UO!O!:type", &name, &PyTuple_Type, &bases,
-                          &PyDict_Type, &orig_dict))
+    if (!PyArg_ParseTuple(args, "UO!O!:type.__new__", &name, &PyTuple_Type,
+                          &bases, &PyDict_Type, &orig_dict))
         return NULL;
 
     /* Determine the proper metatype to deal with this: */