bpo-40792: Make the result of PyNumber_Index() always having exact type int. (GH-20443)

Previously, the result could have been an instance of a subclass of int.

Also revert bpo-26202 and make attributes start, stop and step of the range
object having exact type int.

Add private function _PyNumber_Index() which preserves the old behavior
of PyNumber_Index() for performance to use it in the conversion functions
like PyLong_AsLong().

Author: serhiy-storchaka

Doc/c-api/number.rst

@@ -256,6 +256,10 @@ Number Protocol
    Returns the *o* converted to a Python int on success or ``NULL`` with a
    :exc:`TypeError` exception raised on failure.
 
+   .. versionchanged:: 3.10
+      The result always has exact type :class:`int`.  Previously, the result
+      could have been an instance of a subclass of ``int``.
+
 
 .. c:function:: PyObject* PyNumber_ToBase(PyObject *n, int base)
 

Doc/library/operator.rst

@@ -112,6 +112,10 @@ The mathematical and bitwise operations are the most numerous:
 
    Return *a* converted to an integer.  Equivalent to ``a.__index__()``.
 
+   .. versionchanged:: 3.10
+      The result always has exact type :class:`int`.  Previously, the result
+      could have been an instance of a subclass of ``int``.
+
 
 .. function:: inv(obj)
               invert(obj)

Doc/whatsnew/3.10.rst

@@ -129,6 +129,10 @@ C API Changes
 New Features
 ------------
 
+  The result of :c:func:`PyNumber_Index` now always has exact type :class:`int`.
+  Previously, the result could have been an instance of a subclass of ``int``.
+  (Contributed by Serhiy Storchaka in :issue:`40792`.)
+
 
 Porting to Python 3.10
 ----------------------

Include/cpython/abstract.h

@@ -379,6 +379,9 @@ PyAPI_FUNC(void) _Py_add_one_to_index_C(int nd, Py_ssize_t *index,
 /* Convert Python int to Py_ssize_t. Do nothing if the argument is None. */
 PyAPI_FUNC(int) _Py_convert_optional_to_ssize_t(PyObject *, void *);
 
+/* Same as PyNumber_Index but can return an instance of a subclass of int. */
+PyAPI_FUNC(PyObject *) _PyNumber_Index(PyObject *o);
+
 #ifdef __cplusplus
 }
 #endif

Lib/copy.py

@@ -192,6 +192,7 @@ def _deepcopy_atomic(x, memo):
 d[str] = _deepcopy_atomic
 d[types.CodeType] = _deepcopy_atomic
 d[type] = _deepcopy_atomic
+d[range] = _deepcopy_atomic
 d[types.BuiltinFunctionType] = _deepcopy_atomic
 d[types.FunctionType] = _deepcopy_atomic
 d[weakref.ref] = _deepcopy_atomic

Lib/test/clinic.test

@@ -1332,7 +1332,7 @@ test_Py_ssize_t_converter(PyObject *module, PyObject *const *args, Py_ssize_t na
     }
     {
         Py_ssize_t ival = -1;
-        PyObject *iobj = PyNumber_Index(args[0]);
+        PyObject *iobj = _PyNumber_Index(args[0]);
         if (iobj != NULL) {
             ival = PyLong_AsSsize_t(iobj);
             Py_DECREF(iobj);
@@ -1347,7 +1347,7 @@ test_Py_ssize_t_converter(PyObject *module, PyObject *const *args, Py_ssize_t na
     }
     {
         Py_ssize_t ival = -1;
-        PyObject *iobj = PyNumber_Index(args[1]);
+        PyObject *iobj = _PyNumber_Index(args[1]);
         if (iobj != NULL) {
             ival = PyLong_AsSsize_t(iobj);
             Py_DECREF(iobj);
@@ -1373,7 +1373,7 @@ exit:
 static PyObject *
 test_Py_ssize_t_converter_impl(PyObject *module, Py_ssize_t a, Py_ssize_t b,
                                Py_ssize_t c)
-/*[clinic end generated code: output=ea781bb7169b3436 input=3855f184bb3f299d]*/
+/*[clinic end generated code: output=3bf73f9fdfeab468 input=3855f184bb3f299d]*/
 
 
 /*[clinic input]

Lib/test/test_copy.py

@@ -357,7 +357,7 @@ def f():
             pass
         tests = [None, 42, 2**100, 3.14, True, False, 1j,
                  "hello", "hello\u1234", f.__code__,
-                 NewStyle, Classic, max, property()]
+                 NewStyle, range(10), Classic, max, property()]
         for x in tests:
             self.assertIs(copy.deepcopy(x), x)
 
@@ -579,17 +579,6 @@ class C:
         self.assertIsNot(y, x)
         self.assertIs(y.foo, y)
 
-    def test_deepcopy_range(self):
-        class I(int):
-            pass
-        x = range(I(10))
-        y = copy.deepcopy(x)
-        self.assertIsNot(y, x)
-        self.assertEqual(y, x)
-        self.assertIsNot(y.stop, x.stop)
-        self.assertEqual(y.stop, x.stop)
-        self.assertIsInstance(y.stop, I)
-
     # _reconstruct()
 
     def test_reconstruct_string(self):

Lib/test/test_range.py

@@ -648,11 +648,17 @@ def test_attributes(self):
         self.assert_attrs(range(0, 10, 3), 0, 10, 3)
         self.assert_attrs(range(10, 0, -1), 10, 0, -1)
         self.assert_attrs(range(10, 0, -3), 10, 0, -3)
+        self.assert_attrs(range(True), 0, 1, 1)
+        self.assert_attrs(range(False, True), 0, 1, 1)
+        self.assert_attrs(range(False, True, True), 0, 1, 1)
 
     def assert_attrs(self, rangeobj, start, stop, step):
         self.assertEqual(rangeobj.start, start)
         self.assertEqual(rangeobj.stop, stop)
         self.assertEqual(rangeobj.step, step)
+        self.assertIs(type(rangeobj.start), int)
+        self.assertIs(type(rangeobj.stop), int)
+        self.assertIs(type(rangeobj.step), int)
 
         with self.assertRaises(AttributeError):
             rangeobj.start = 0

Misc/NEWS.d/next/C API/2020-05-27-11-02-15.bpo-40792.pBw2Bb.rst

@@ -0,0 +1,2 @@
+The result of :c:func:`PyNumber_Index` now always has exact type :class:`int`.
+Previously, the result could have been an instance of a subclass of ``int``.

Misc/NEWS.d/next/Core and Builtins/2020-05-27-22-37-58.bpo-40792.WEDqqU.rst

@@ -0,0 +1,3 @@
+Attributes ``start``, ``stop`` and ``step`` of the :class:`range` object now
+always has exact type :class:`int`.  Previously, they could have been an
+instance of a subclass of ``int``.