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jdemeyermarkshannon
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encukou
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bpo-36922: implement PEP-590 Py_TPFLAGS_METHOD_DESCRIPTOR (GH-13338)
Co-authored-by: Mark Shannon <mark@hotpy.org>
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‎Doc/c-api/typeobj.rst

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@@ -1045,6 +1045,32 @@ and :c:type:`PyType_Type` effectively act as defaults.)
10451045

10461046
???
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.. data:: Py_TPFLAGS_METHOD_DESCRIPTOR
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This bit indicates that objects behave like unbound methods.
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If this flag is set for ``type(meth)``, then:
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- ``meth.__get__(obj, cls)(*args, **kwds)`` (with ``obj`` not None)
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must be equivalent to ``meth(obj, *args, **kwds)``.
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- ``meth.__get__(None, cls)(*args, **kwds)``
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must be equivalent to ``meth(*args, **kwds)``.
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This flag enables an optimization for typical method calls like
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``obj.meth()``: it avoids creating a temporary "bound method" object for
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``obj.meth``.
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.. versionadded:: 3.8
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**Inheritance:**
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This flag is never inherited by heap types.
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For extension types, it is inherited whenever
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:c:member:`~PyTypeObject.tp_descr_get` is inherited.
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.. XXX Document more flags here?
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10501076

‎Include/object.h

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@@ -307,6 +307,9 @@ given type object has a specified feature.
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#define Py_TPFLAGS_HAVE_STACKLESS_EXTENSION 0
308308
#endif
309309

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/* Objects behave like an unbound method */
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#define Py_TPFLAGS_METHOD_DESCRIPTOR (1UL << 17)
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310313
/* Objects support type attribute cache */
311314
#define Py_TPFLAGS_HAVE_VERSION_TAG (1UL << 18)
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#define Py_TPFLAGS_VALID_VERSION_TAG (1UL << 19)

‎Lib/test/test_capi.py

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@@ -27,6 +27,8 @@
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# Were we compiled --with-pydebug or with #define Py_DEBUG?
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Py_DEBUG = hasattr(sys, 'gettotalrefcount')
2929

30+
Py_TPFLAGS_METHOD_DESCRIPTOR = 1 << 17
31+
3032

3133
def testfunction(self):
3234
"""some doc"""
@@ -456,6 +458,28 @@ def test_pendingcalls_non_threaded(self):
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self.pendingcalls_wait(l, n)
457459

458460

461+
class TestPEP590(unittest.TestCase):
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def test_method_descriptor_flag(self):
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import functools
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cached = functools.lru_cache(1)(testfunction)
466+
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self.assertFalse(type(repr).__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertTrue(type(list.append).__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertTrue(type(list.__add__).__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertTrue(type(testfunction).__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertTrue(type(cached).__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertTrue(_testcapi.MethodDescriptorBase.__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertTrue(_testcapi.MethodDescriptorDerived.__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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self.assertFalse(_testcapi.MethodDescriptorNopGet.__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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# Heap type should not inherit Py_TPFLAGS_METHOD_DESCRIPTOR
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class MethodDescriptorHeap(_testcapi.MethodDescriptorBase):
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pass
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self.assertFalse(MethodDescriptorHeap.__flags__ & Py_TPFLAGS_METHOD_DESCRIPTOR)
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482+
459483
class SubinterpreterTest(unittest.TestCase):
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461485
def test_subinterps(self):

‎Misc/NEWS.d/next/C API/2019-05-15-10-46-55.bpo-36922.J3EFK_.rst

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@@ -0,0 +1,3 @@
1+
Add new type flag ``Py_TPFLAGS_METHOD_DESCRIPTOR`` for objects behaving like
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unbound methods. These are objects supporting the optimization given by the
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``LOAD_METHOD``/``CALL_METHOD`` opcodes. See PEP 590.

‎Modules/_functoolsmodule.c

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1333,7 +1333,8 @@ static PyTypeObject lru_cache_type = {
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0, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
1336-
Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE|Py_TPFLAGS_HAVE_GC,
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
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Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_METHOD_DESCRIPTOR,
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/* tp_flags */
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lru_cache_doc, /* tp_doc */
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(traverseproc)lru_cache_tp_traverse,/* tp_traverse */

‎Modules/_testcapimodule.c

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Original file line numberDiff line numberDiff line change
@@ -5787,6 +5787,46 @@ static PyTypeObject Generic_Type = {
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};
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57895789

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/* Test PEP 590 */
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static PyObject *
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func_descr_get(PyObject *func, PyObject *obj, PyObject *type)
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{
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if (obj == Py_None || obj == NULL) {
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Py_INCREF(func);
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return func;
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}
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return PyMethod_New(func, obj);
5800+
}
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5802+
static PyObject *
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nop_descr_get(PyObject *func, PyObject *obj, PyObject *type)
5804+
{
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Py_INCREF(func);
5806+
return func;
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}
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5809+
static PyTypeObject MethodDescriptorBase_Type = {
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PyVarObject_HEAD_INIT(NULL, 0)
5811+
"MethodDescriptorBase",
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_METHOD_DESCRIPTOR,
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.tp_descr_get = func_descr_get,
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};
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5816+
static PyTypeObject MethodDescriptorDerived_Type = {
5817+
PyVarObject_HEAD_INIT(NULL, 0)
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"MethodDescriptorDerived",
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
5820+
};
5821+
5822+
static PyTypeObject MethodDescriptorNopGet_Type = {
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PyVarObject_HEAD_INIT(NULL, 0)
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"MethodDescriptorNopGet",
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
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.tp_descr_get = nop_descr_get,
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};
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5829+
57905830
static struct PyModuleDef _testcapimodule = {
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PyModuleDef_HEAD_INIT,
57925832
"_testcapi",
@@ -5834,6 +5874,23 @@ PyInit__testcapi(void)
58345874
Py_INCREF(&MyList_Type);
58355875
PyModule_AddObject(m, "MyList", (PyObject *)&MyList_Type);
58365876

5877+
if (PyType_Ready(&MethodDescriptorBase_Type) < 0)
5878+
return NULL;
5879+
Py_INCREF(&MethodDescriptorBase_Type);
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PyModule_AddObject(m, "MethodDescriptorBase", (PyObject *)&MethodDescriptorBase_Type);
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5882+
MethodDescriptorDerived_Type.tp_base = &MethodDescriptorBase_Type;
5883+
if (PyType_Ready(&MethodDescriptorDerived_Type) < 0)
5884+
return NULL;
5885+
Py_INCREF(&MethodDescriptorDerived_Type);
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PyModule_AddObject(m, "MethodDescriptorDerived", (PyObject *)&MethodDescriptorDerived_Type);
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5888+
MethodDescriptorNopGet_Type.tp_base = &MethodDescriptorBase_Type;
5889+
if (PyType_Ready(&MethodDescriptorNopGet_Type) < 0)
5890+
return NULL;
5891+
Py_INCREF(&MethodDescriptorNopGet_Type);
5892+
PyModule_AddObject(m, "MethodDescriptorNopGet", (PyObject *)&MethodDescriptorNopGet_Type);
5893+
58375894
if (PyType_Ready(&GenericAlias_Type) < 0)
58385895
return NULL;
58395896
Py_INCREF(&GenericAlias_Type);

‎Objects/descrobject.c

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Original file line numberDiff line numberDiff line change
@@ -556,7 +556,8 @@ PyTypeObject PyMethodDescr_Type = {
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PyObject_GenericGetAttr, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
559-
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
559+
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
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Py_TPFLAGS_METHOD_DESCRIPTOR, /* tp_flags */
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0, /* tp_doc */
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descr_traverse, /* tp_traverse */
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0, /* tp_clear */
@@ -705,7 +706,8 @@ PyTypeObject PyWrapperDescr_Type = {
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PyObject_GenericGetAttr, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
708-
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
709+
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
710+
Py_TPFLAGS_METHOD_DESCRIPTOR, /* tp_flags */
709711
0, /* tp_doc */
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descr_traverse, /* tp_traverse */
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0, /* tp_clear */

‎Objects/funcobject.c

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@@ -663,7 +663,8 @@ PyTypeObject PyFunction_Type = {
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0, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
666-
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
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Py_TPFLAGS_METHOD_DESCRIPTOR, /* tp_flags */
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func_new__doc__, /* tp_doc */
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(traverseproc)func_traverse, /* tp_traverse */
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(inquiry)func_clear, /* tp_clear */

‎Objects/object.c

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@@ -1155,8 +1155,7 @@ _PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
11551155
descr = _PyType_Lookup(tp, name);
11561156
if (descr != NULL) {
11571157
Py_INCREF(descr);
1158-
if (PyFunction_Check(descr) ||
1159-
(Py_TYPE(descr) == &PyMethodDescr_Type)) {
1158+
if (PyType_HasFeature(Py_TYPE(descr), Py_TPFLAGS_METHOD_DESCRIPTOR)) {
11601159
meth_found = 1;
11611160
} else {
11621161
f = descr->ob_type->tp_descr_get;

‎Objects/typeobject.c

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@@ -4950,7 +4950,7 @@ static void
49504950
inherit_special(PyTypeObject *type, PyTypeObject *base)
49514951
{
49524952

4953-
/* Copying basicsize is connected to the GC flags */
4953+
/* Copying tp_traverse and tp_clear is connected to the GC flags */
49544954
if (!(type->tp_flags & Py_TPFLAGS_HAVE_GC) &&
49554955
(base->tp_flags & Py_TPFLAGS_HAVE_GC) &&
49564956
(!type->tp_traverse && !type->tp_clear)) {
@@ -5165,6 +5165,15 @@ inherit_slots(PyTypeObject *type, PyTypeObject *base)
51655165
}
51665166
{
51675167
COPYSLOT(tp_descr_get);
5168+
/* Inherit Py_TPFLAGS_METHOD_DESCRIPTOR if tp_descr_get was inherited,
5169+
* but only for extension types */
5170+
if (base->tp_descr_get &&
5171+
type->tp_descr_get == base->tp_descr_get &&
5172+
!(type->tp_flags & Py_TPFLAGS_HEAPTYPE) &&
5173+
(base->tp_flags & Py_TPFLAGS_METHOD_DESCRIPTOR))
5174+
{
5175+
type->tp_flags |= Py_TPFLAGS_METHOD_DESCRIPTOR;
5176+
}
51685177
COPYSLOT(tp_descr_set);
51695178
COPYSLOT(tp_dictoffset);
51705179
COPYSLOT(tp_init);

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