add support for 3.13

Author: kumaraditya303

docs/api.rst

@@ -74,7 +74,7 @@ Python 3.15
 
    See `PyUnstable_SetImmortal() documentation  <https://docs.python.org/dev/c-api/object.html#c.PyUnstable_SetImmortal>`__.
 
-   Availability: Python 3.14 and newer, not available on PyPy.
+   Availability: Python 3.13 and newer, not available on PyPy.
 
 Python 3.14
 -----------

pythoncapi_compat.h

@@ -2659,11 +2659,11 @@ PyUnstable_Unicode_GET_CACHED_HASH(PyObject *op)
 }
 #endif
 
-#if 0x030E0000 <= PY_VERSION_HEX && PY_VERSION_HEX < 0x030F00A7 && !defined(PYPY_VERSION)
+#if 0x030D0000 <= PY_VERSION_HEX && PY_VERSION_HEX < 0x030F00A7 && !defined(PYPY_VERSION)
 // Immortal objects were implemented in Python 3.12, however there is no easy API
 // to make objects immortal until 3.14 which has _Py_SetImmortal(). Since
 // immortal objects are primarily needed for free-threading, this API is implemented
-// for 3.14 and above.
+// for 3.14 using _Py_SetImmortal() and uses private macros on 3.13.
 static inline int
 PyUnstable_SetImmortal(PyObject *op)
 {
@@ -2673,7 +2673,21 @@ PyUnstable_SetImmortal(PyObject *op)
     if (!PyUnstable_Object_IsUniquelyReferenced(op) || PyUnicode_Check(op)) {
         return 0;
     }
-    _Py_SetImmortal(op);
+#if 0x030E0000 <= PY_VERSION_HEX
+     _Py_SetImmortal(op);
+#else
+    // Python 3.13 doesn't export _Py_SetImmortal() function
+    if (PyObject_GC_IsTracked(op)) {
+        PyObject_GC_UnTrack(op);
+    }
+#ifdef Py_GIL_DISABLED
+    op->ob_tid = _Py_UNOWNED_TID;
+    op->ob_ref_local = _Py_IMMORTAL_REFCNT_LOCAL;
+    op->ob_ref_shared = 0;
+#else
+    op->ob_refcnt = _Py_IMMORTAL_REFCNT;
+#endif
+#endif
     return 1;
 }
 #endif

tests/test_pythoncapi_compat_cext.c

@@ -2489,7 +2489,7 @@ test_try_incref(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     Py_RETURN_NONE;
 }
 
-#if 0x030E0000 <= PY_VERSION_HEX && !defined(PYPY_VERSION)
+#if 0x030D0000 <= PY_VERSION_HEX && !defined(PYPY_VERSION)
 static PyObject *
 test_set_immortal(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
 {
@@ -2579,7 +2579,7 @@ static struct PyMethodDef methods[] = {
     {"test_byteswriter", test_byteswriter, METH_NOARGS, _Py_NULL},
     {"test_tuple", test_tuple, METH_NOARGS, _Py_NULL},
     {"test_try_incref", test_try_incref, METH_NOARGS, _Py_NULL},
-#if 0x030E0000 <= PY_VERSION_HEX && !defined(PYPY_VERSION)
+#if 0x030D0000 <= PY_VERSION_HEX && !defined(PYPY_VERSION)
     {"test_set_immortal", test_set_immortal, METH_NOARGS, _Py_NULL},
 #endif
     {_Py_NULL, _Py_NULL, 0, _Py_NULL}