gh-132987: Support __index__() for "k" and "K" formats in PyArg_Parse

Doc/c-api/arg.rst

@@ -274,13 +274,19 @@ small to receive the value.
    Convert a Python integer to a C :c:expr:`unsigned long` without
    overflow checking.
 
+   .. versionchanged:: next
+      Use :meth:`~object.__index__` if available.
+
 ``L`` (:class:`int`) [long long]
    Convert a Python integer to a C :c:expr:`long long`.
 
 ``K`` (:class:`int`) [unsigned long long]
    Convert a Python integer to a C :c:expr:`unsigned long long`
    without overflow checking.
 
+   .. versionchanged:: next
+      Use :meth:`~object.__index__` if available.
+
 ``n`` (:class:`int`) [:c:type:`Py_ssize_t`]
    Convert a Python integer to a C :c:type:`Py_ssize_t`.
 

Doc/whatsnew/3.14.rst

@@ -2073,6 +2073,11 @@ New features
   Adding ``?`` after any format unit makes ``None`` be accepted as a value.
   (Contributed by Serhiy Storchaka in :gh:`112068`.)
 
+* The ``k`` and ``K`` formats in :c:func:`PyArg_ParseTuple` and
+  similar functions use now :meth:`~object.__index__` if available,
+  as all other integer formats.
+  (Contributed by Serhiy Storchaka in :gh:`112068`.)
+
 * Add macros :c:func:`Py_PACK_VERSION` and :c:func:`Py_PACK_FULL_VERSION` for
   bit-packing Python version numbers.
   (Contributed by Petr Viktorin in :gh:`128629`.)

Lib/test/test_capi/test_getargs.py

@@ -267,12 +267,12 @@ def test_I(self):
     def test_k(self):
         from _testcapi import getargs_k
         # k returns 'unsigned long', no range checking
-        # it does not accept float, or instances with __int__
         self.assertRaises(TypeError, getargs_k, 3.14)
-        self.assertRaises(TypeError, getargs_k, Index())
+        self.assertEqual(99, getargs_k(Index()))
         self.assertEqual(0, getargs_k(IndexIntSubclass()))
         self.assertRaises(TypeError, getargs_k, BadIndex())
-        self.assertRaises(TypeError, getargs_k, BadIndex2())
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(1, getargs_k(BadIndex2()))
         self.assertEqual(0, getargs_k(BadIndex3()))
         self.assertRaises(TypeError, getargs_k, Int())
         self.assertEqual(0, getargs_k(IntSubclass()))
@@ -419,10 +419,11 @@ def test_K(self):
         from _testcapi import getargs_K
         # K return 'unsigned long long', no range checking
         self.assertRaises(TypeError, getargs_K, 3.14)
-        self.assertRaises(TypeError, getargs_K, Index())
+        self.assertEqual(99, getargs_K(Index()))
         self.assertEqual(0, getargs_K(IndexIntSubclass()))
         self.assertRaises(TypeError, getargs_K, BadIndex())
-        self.assertRaises(TypeError, getargs_K, BadIndex2())
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(1, getargs_K(BadIndex2()))
         self.assertEqual(0, getargs_K(BadIndex3()))
         self.assertRaises(TypeError, getargs_K, Int())
         self.assertEqual(0, getargs_K(IntSubclass()))
@@ -432,6 +433,7 @@ def test_K(self):
 
         self.assertEqual(ULLONG_MAX, getargs_K(ULLONG_MAX))
         self.assertEqual(0, getargs_K(0))
+        self.assertEqual(ULLONG_MAX, getargs_K(ULLONG_MAX))
         self.assertEqual(0, getargs_K(ULLONG_MAX+1))
 
         self.assertEqual(42, getargs_K(42))

Misc/NEWS.d/next/C_API/2025-04-26-12-00-52.gh-issue-132987.vykZGN.rst

@@ -0,0 +1,2 @@
+The ``k`` and ``K`` formats in :c:func:`PyArg_Parse` support now the
+:meth:`~object.__index__` special method, as all other integer formats.

Python/getargs.c

@@ -839,10 +839,13 @@ convertsimple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
         unsigned long *p = va_arg(*p_va, unsigned long *);
         HANDLE_NULLABLE;
         unsigned long ival;
-        if (PyLong_Check(arg))
-            ival = PyLong_AsUnsignedLongMask(arg);
-        else
+        if (!PyIndex_Check(arg)) {
             return converterr(nullable, "int", arg, msgbuf, bufsize);
+        }
+        ival = PyLong_AsUnsignedLongMask(arg);
+        if (ival == (unsigned long)(long)-1 && PyErr_Occurred()) {
+            RETURN_ERR_OCCURRED;
+        }
         *p = ival;
         break;
     }
@@ -862,10 +865,13 @@ convertsimple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
         unsigned long long *p = va_arg(*p_va, unsigned long long *);
         HANDLE_NULLABLE;
         unsigned long long ival;
-        if (PyLong_Check(arg))
-            ival = PyLong_AsUnsignedLongLongMask(arg);
-        else
+        if (!PyIndex_Check(arg)) {
             return converterr(nullable, "int", arg, msgbuf, bufsize);
+        }
+        ival = PyLong_AsUnsignedLongLongMask(arg);
+        if (ival == (unsigned long long)(long long)-1 && PyErr_Occurred()) {
+            RETURN_ERR_OCCURRED;
+        }
         *p = ival;
         break;
     }

Tools/clinic/libclinic/converters.py

@@ -386,7 +386,7 @@ def use_converter(self) -> None:
     def parse_arg(self, argname: str, displayname: str, *, limited_capi: bool) -> str | None:
         if self.format_unit == 'k':
             return self.format_code("""
-                if (!PyLong_Check({argname})) {{{{
+                if (!PyIndex_Check({argname})) {{{{
                     {bad_argument}
                     goto exit;
                 }}}}
@@ -444,7 +444,7 @@ def use_converter(self) -> None:
     def parse_arg(self, argname: str, displayname: str, *, limited_capi: bool) -> str | None:
         if self.format_unit == 'K':
             return self.format_code("""
-                if (!PyLong_Check({argname})) {{{{
+                if (!PyIndex_Check({argname})) {{{{
                     {bad_argument}
                     goto exit;
                 }}}}