gh-108444: Add PyLong_AsInt() public function

* Rename _PyLong_AsInt() to PyLong_AsInt().
* Add documentation.
* Add test.
* For now, keep _PyLong_AsInt() as an alias to PyLong_AsInt().

Author: vstinner

Doc/c-api/long.rst

@@ -136,6 +136,14 @@ distinguished from a number.  Use :c:func:`PyErr_Occurred` to disambiguate.
       This function will no longer use :meth:`~object.__int__`.
 
 
+.. c:function:: int PyLong_AsInt(PyObject *obj)
+
+   Similar to :c:func:`PyLong_AsLong`, but store the result in a C
+   :c:type:`int` instead of a C :c:type:`long`.
+
+   .. versionadded:: 3.13
+
+
 .. c:function:: long PyLong_AsLongAndOverflow(PyObject *obj, int *overflow)
 
    Return a C :c:expr:`long` representation of *obj*.  If *obj* is not an

Doc/whatsnew/3.13.rst

@@ -871,6 +871,12 @@ New Features
   :term:`shutting down <interpreter shutdown>`.
   (Contributed by Victor Stinner in :gh:`108014`.)
 
+* Add :c:func:`PyLong_AsInt` function: similar to :c:func:`PyLong_AsLong`, but
+  store the result in a C :c:type:`int` instead of a C :c:type:`long`.
+  Previously, it was known as the the private function :c:func:`!_PyLong_AsInt`
+  (with an underscore prefix).
+  (Contributed by Victor Stinner in :gh:`108014`.)
+
 Porting to Python 3.13
 ----------------------
 

Include/cpython/longobject.h

@@ -2,7 +2,8 @@
 #  error "this header file must not be included directly"
 #endif
 
-PyAPI_FUNC(int) _PyLong_AsInt(PyObject *);
+// Alias for backport compatibility
+#define _PyLong_AsInt PyLong_AsInt
 
 PyAPI_FUNC(int) _PyLong_UnsignedShort_Converter(PyObject *, void *);
 PyAPI_FUNC(int) _PyLong_UnsignedInt_Converter(PyObject *, void *);

Include/longobject.h

@@ -18,6 +18,7 @@ PyAPI_FUNC(PyObject *) PyLong_FromUnsignedLong(unsigned long);
 PyAPI_FUNC(PyObject *) PyLong_FromSize_t(size_t);
 PyAPI_FUNC(PyObject *) PyLong_FromSsize_t(Py_ssize_t);
 PyAPI_FUNC(PyObject *) PyLong_FromDouble(double);
+PyAPI_FUNC(int) PyLong_AsInt(PyObject *);
 PyAPI_FUNC(long) PyLong_AsLong(PyObject *);
 PyAPI_FUNC(long) PyLong_AsLongAndOverflow(PyObject *, int *);
 PyAPI_FUNC(Py_ssize_t) PyLong_AsSsize_t(PyObject *);

Lib/test/test_capi/test_long.py

@@ -34,6 +34,28 @@ def test_compact_known(self):
         self.assertEqual(_testcapi.call_long_compact_api(sys.maxsize),
                          (False, -1))
 
+    def test_long_asint(self):
+        PyLong_AsInt = _testcapi.PyLong_AsInt
+        INT_MIN = _testcapi.INT_MIN
+        INT_MAX = _testcapi.INT_MAX
+
+        # round trip (object -> int -> object)
+        for value in (INT_MIN, INT_MAX, -1, 0, 1, 123):
+            with self.subTest(value=value):
+                self.assertEqual(PyLong_AsInt(value), value)
+
+        # bound checking
+        with self.assertRaises(OverflowError):
+            PyLong_AsInt(INT_MIN - 1)
+        with self.assertRaises(OverflowError):
+            PyLong_AsInt(INT_MAX + 1)
+
+        # invalid type
+        for value in (1.0, b'2', '3'):
+            with self.subTest(value=value):
+                with self.assertRaises(TypeError):
+                    PyLong_AsInt(value)
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/C API/2023-08-24-20-08-02.gh-issue-108014.20DOSS.rst

@@ -0,0 +1,5 @@
+Add :c:func:`PyLong_AsInt` function: similar to :c:func:`PyLong_AsLong`, but
+store the result in a C :c:type:`int` instead of a C :c:type:`long`.
+Previously, it was known as the the private function
+:c:func:`!_PyLong_AsInt` (with an underscore prefix). Patch by by Victor
+Stinner.

Modules/_testcapi/clinic/long.c.h

@@ -37,6 +37,9 @@ raise_test_long_error(const char* msg)
     return raiseTestError("test_long_api", msg);
 }
 
+// Test PyLong_FromLong()/PyLong_AsLong()
+// and PyLong_FromUnsignedLong()/PyLong_AsUnsignedLong().
+
 #define TESTNAME        test_long_api_inner
 #define TYPENAME        long
 #define F_S_TO_PY       PyLong_FromLong
@@ -64,6 +67,9 @@ _testcapi_test_long_api_impl(PyObject *module)
 #undef F_U_TO_PY
 #undef F_PY_TO_U
 
+// Test PyLong_FromLongLong()/PyLong_AsLongLong()
+// and PyLong_FromUnsignedLongLong()/PyLong_AsUnsignedLongLong().
+
 static PyObject *
 raise_test_longlong_error(const char* msg)
 {
@@ -595,6 +601,24 @@ _testcapi_call_long_compact_api(PyObject *module, PyObject *arg)
     return Py_BuildValue("in", is_compact, value);
 }
 
+/*[clinic input]
+_testcapi.PyLong_AsInt
+    arg: object
+    /
+[clinic start generated code]*/
+
+static PyObject *
+_testcapi_PyLong_AsInt(PyObject *module, PyObject *arg)
+/*[clinic end generated code: output=0df9f19de5fa575b input=9561b97105493a67]*/
+{
+    assert(!PyErr_Occurred());
+    int value = PyLong_AsInt(arg);
+    if (value == -1 && PyErr_Occurred()) {
+        return NULL;
+    }
+    return PyLong_FromLong(value);
+}
+
 static PyMethodDef test_methods[] = {
     _TESTCAPI_TEST_LONG_AND_OVERFLOW_METHODDEF
     _TESTCAPI_TEST_LONG_API_METHODDEF
@@ -605,6 +629,7 @@ static PyMethodDef test_methods[] = {
     _TESTCAPI_TEST_LONG_NUMBITS_METHODDEF
     _TESTCAPI_TEST_LONGLONG_API_METHODDEF
     _TESTCAPI_CALL_LONG_COMPACT_API_METHODDEF
+    _TESTCAPI_PYLONG_ASINT_METHODDEF
     {NULL},
 };
 

Modules/_testcapi/long.c

@@ -549,7 +549,7 @@ PyLong_AsLong(PyObject *obj)
    method.  Return -1 and set an error if overflow occurs. */
 
 int
-_PyLong_AsInt(PyObject *obj)
+PyLong_AsInt(PyObject *obj)
 {
     int overflow;
     long result = PyLong_AsLongAndOverflow(obj, &overflow);