Add PyObject_GetOptionalAttr() function

Author: vstinner

Diff for: docs/api.rst

@@ -35,6 +35,15 @@ Python 3.13
 
    See `PyWeakref_GetRef() documentation <https://docs.python.org/dev/c-api/weakref.html#c.PyWeakref_GetRef>`__.
 
+.. c:function:: int PyObject_GetOptionalAttr(PyObject *obj, PyObject *attr_name, PyObject **result)
+
+   See `PyObject_GetOptionalAttr() documentation <https://docs.python.org/dev/c-api/object.html#c.PyObject_GetOptionalAttr>`__.
+
+.. c:function:: int PyObject_GetOptionalAttrString(PyObject *obj, const char *name, PyObject **result)
+
+   See `PyObject_GetOptionalAttrString() documentation <https://docs.python.org/dev/c-api/object.html#c.PyObject_GetOptionalAttrString>`__.
+
+
 Python 3.12
 -----------
 

Diff for: docs/changelog.rst

@@ -1,6 +1,8 @@
 Changelog
 =========
 
+* 2023-07-12: Add ``PyObject_GetOptionalAttr()`` and
+  ``PyObject_GetOptionalAttrString()`` functions.
 * 2023-07-05: Add ``PyObject_Vectorcall()`` function.
 * 2023-06-21: Add ``PyWeakref_GetRef()`` function.
 * 2023-06-20: Add ``PyImport_AddModuleRef()`` function.

Diff for: pythoncapi_compat.h

@@ -698,6 +698,49 @@ PyObject_Vectorcall(PyObject *callable, PyObject *const *args,
 #endif
 
 
+// gh-106521 added PyObject_GetOptionalAttr() to Python 3.13.0a1
+#if PY_VERSION_HEX < 0x030D00A1
+PYCAPI_COMPAT_STATIC_INLINE(int)
+PyObject_GetOptionalAttr(PyObject *obj, PyObject *name, PyObject **result)
+{
+    // bpo-32571 added _PyObject_LookupAttr() to Python 3.7.0b1
+#if PY_VERSION_HEX >= 0x030700B1 && !defined(PYPY_VERSION)
+    return _PyObject_LookupAttr(obj, name, result);
+#else
+    *result = PyObject_GetAttr(obj, name);
+    if (*result != NULL) {
+        return 1;
+    }
+    if (!PyErr_Occurred()) {
+        return 0;
+    }
+    if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+        PyErr_Clear();
+        return 0;
+    }
+    return -1;
+#endif
+}
+
+PYCAPI_COMPAT_STATIC_INLINE(int)
+PyObject_GetOptionalAttrString(PyObject *obj, const char *name, PyObject **presult)
+{
+    PyObject *name_obj;
+#if PY_VERSION_HEX >= 0x03000000
+    name_obj = PyUnicode_FromString(name);
+#else
+    name_obj = PyString_FromString(name);
+#endif
+    if (name_obj == NULL) {
+        return -1;
+    }
+    int res = PyObject_GetOptionalAttr(obj, name_obj, presult);
+    Py_DECREF(name_obj);
+    return res;
+}
+#endif
+
+
 #ifdef __cplusplus
 }
 #endif

Diff for: tests/test_pythoncapi_compat_cext.c

@@ -50,6 +50,21 @@
 #  define ASSERT_REFCNT(expr)
 #endif
 
+
+static PyObject*
+create_string(const char *str)
+{
+    PyObject *obj;
+#ifdef PYTHON3
+    obj = PyUnicode_FromString(str);
+#else
+    obj = PyString_FromString(str);
+#endif
+    assert(obj != NULL);
+    return obj;
+}
+
+
 static PyObject *
 test_object(PyObject *Py_UNUSED(module), PyObject* Py_UNUSED(ignored))
 {
@@ -930,6 +945,51 @@ test_vectorcall(PyObject *module, PyObject *Py_UNUSED(args))
 }
 
 
+static PyObject *
+test_getattr(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
+{
+    assert(!PyErr_Occurred());
+
+    PyObject *obj = PyImport_ImportModule("sys");
+    if (obj == NULL) {
+        return NULL;
+    }
+    PyObject *attr_name;
+    PyObject *value;
+
+    // test PyObject_GetOptionalAttr(): attribute exists
+    attr_name = create_string("version");
+    value = Py_True;  // marker value
+    assert(PyObject_GetOptionalAttr(obj, attr_name, &value) == 1);
+    assert(value != NULL);
+    Py_DECREF(value);
+    Py_DECREF(attr_name);
+
+    // test PyObject_GetOptionalAttrString(): attribute exists
+    value = Py_True;  // marker value
+    assert(PyObject_GetOptionalAttrString(obj, "version", &value) == 1);
+    assert(value != NULL);
+    Py_DECREF(value);
+
+    // test PyObject_GetOptionalAttr(): attribute doesn't exist
+    attr_name = create_string("nonexistant_attr_name");
+    value = Py_True;  // marker value
+    assert(PyObject_GetOptionalAttr(obj, attr_name, &value) == 0);
+    assert(value == NULL);
+    Py_DECREF(attr_name);
+    assert(!PyErr_Occurred());
+
+    // test PyObject_GetOptionalAttrString(): attribute doesn't exist
+    value = Py_True;  // marker value
+    assert(PyObject_GetOptionalAttrString(obj, "nonexistant_attr_name", &value) == 0);
+    assert(value == NULL);
+    assert(!PyErr_Occurred());
+
+    Py_DECREF(obj);
+    Py_RETURN_NONE;
+}
+
+
 static struct PyMethodDef methods[] = {
     {"test_object", test_object, METH_NOARGS, _Py_NULL},
     {"test_py_is", test_py_is, METH_NOARGS, _Py_NULL},
@@ -952,6 +1012,7 @@ static struct PyMethodDef methods[] = {
     {"test_weakref", test_weakref, METH_NOARGS, _Py_NULL},
     {"func_varargs", (PyCFunction)(void*)func_varargs, METH_VARARGS | METH_KEYWORDS, _Py_NULL},
     {"test_vectorcall", test_vectorcall, METH_NOARGS, _Py_NULL},
+    {"test_getattr", test_getattr, METH_NOARGS, _Py_NULL},
     {_Py_NULL, _Py_NULL, 0, _Py_NULL}
 };