gh-106004: Add PyDict_GetItemRef() function (#106005)

* Add PyDict_GetItemRef() and PyDict_GetItemStringRef() functions.
  Add these functions to the stable ABI version 3.13.
* Add unit tests on the PyDict C API in test_capi.

Doc/c-api/dict.rst

@@ -93,10 +93,26 @@ Dictionary Objects
    Return ``0`` on success or ``-1`` on failure.
 
 
+.. c:function:: int PyDict_GetItemRef(PyObject *p, PyObject *key, PyObject **result)
+
+   Return a new :term:`strong reference` to the object from dictionary *p*
+   which has a key *key*:
+
+   * If the key is present, set *\*result* to a new :term:`strong reference`
+     to the value and return ``1``.
+   * If the key is missing, set *\*result* to ``NULL`` and return ``0``.
+   * On error, raise an exception and return ``-1``.
+
+   .. versionadded:: 3.13
+
+   See also the :c:func:`PyObject_GetItem` function.
+
+
 .. c:function:: PyObject* PyDict_GetItem(PyObject *p, PyObject *key)
 
-   Return the object from dictionary *p* which has a key *key*.  Return ``NULL``
-   if the key *key* is not present, but *without* setting an exception.
+   Return a :term:`borrowed reference` to the object from dictionary *p* which
+   has a key *key*.  Return ``NULL`` if the key *key* is missing *without*
+   setting an exception.
 
    .. note::
 
@@ -131,6 +147,14 @@ Dictionary Objects
       :c:func:`PyUnicode_FromString` *key* instead.
 
 
+.. c:function:: int PyDict_GetItemStringRef(PyObject *p, const char *key, PyObject **result)
+
+   Similar than :c:func:`PyDict_GetItemRef`, but *key* is specified as a
+   :c:expr:`const char*`, rather than a :c:expr:`PyObject*`.
+
+   .. versionadded:: 3.13
+
+
 .. c:function:: PyObject* PyDict_SetDefault(PyObject *p, PyObject *key, PyObject *defaultobj)
 
    This is the same as the Python-level :meth:`dict.setdefault`.  If present, it

Doc/whatsnew/3.13.rst

@@ -786,6 +786,13 @@ New Features
   always steals a reference to the value.
   (Contributed by Serhiy Storchaka in :gh:`86493`.)
 
+* Added :c:func:`PyDict_GetItemRef` and :c:func:`PyDict_GetItemStringRef`
+  functions: similar to :c:func:`PyDict_GetItemWithError` but returning a
+  :term:`strong reference` instead of a :term:`borrowed reference`. Moreover,
+  these functions return -1 on error and so checking ``PyErr_Occurred()`` is
+  not needed.
+  (Contributed by Victor Stinner in :gh:`106004`.)
+
 Porting to Python 3.13
 ----------------------
 

Include/dictobject.h

@@ -57,6 +57,15 @@ PyAPI_FUNC(int) PyDict_MergeFromSeq2(PyObject *d,
 PyAPI_FUNC(PyObject *) PyDict_GetItemString(PyObject *dp, const char *key);
 PyAPI_FUNC(int) PyDict_SetItemString(PyObject *dp, const char *key, PyObject *item);
 PyAPI_FUNC(int) PyDict_DelItemString(PyObject *dp, const char *key);
+
+// Return the object from dictionary *op* which has a key *key*.
+// - If the key is present, set *result to a new strong reference to the value
+//   and return 1.
+// - If the key is missing, set *result to NULL and return 0 .
+// - On error, raise an exception and return -1.
+PyAPI_FUNC(int) PyDict_GetItemRef(PyObject *mp, PyObject *key, PyObject **result);
+PyAPI_FUNC(int) PyDict_GetItemStringRef(PyObject *mp, const char *key, PyObject **result);
+
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030A0000
 PyAPI_FUNC(PyObject *) PyObject_GenericGetDict(PyObject *, void *);
 #endif

Misc/NEWS.d/next/C API/2023-06-23-02-57-15.gh-issue-106004.-OToh6.rst

@@ -0,0 +1,4 @@
+Adds :c:func:`PyDict_GetItemRef` and :c:func:`PyDict_GetItemStringRef`
+functions: similar to :c:func:`PyDict_GetItemWithError` but returning a
+:term:`strong reference` instead of a :term:`borrowed reference`. Patch by
+Victor Stinner.

Misc/stable_abi.toml

@@ -2446,3 +2446,7 @@
     added = '3.13'
 [function.PyModule_Add]
     added = '3.13'
+[function.PyDict_GetItemRef]
+    added = '3.13'
+[function.PyDict_GetItemStringRef]
+    added = '3.13'

Modules/_testcapimodule.c

@@ -3464,6 +3464,196 @@ test_weakref_capi(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
 }
 
 
+static PyObject *
+test_dict_capi(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
+{
+    assert(!PyErr_Occurred());
+
+    PyObject *dict= NULL, *key = NULL, *missing_key = NULL, *value = NULL;
+    PyObject *invalid_key = NULL;
+    int res;
+
+    // test PyDict_New()
+    dict = PyDict_New();
+    if (dict == NULL) {
+        goto error;
+    }
+
+    key = PyUnicode_FromString("key");
+    if (key == NULL) {
+        goto error;
+    }
+
+    missing_key = PyUnicode_FromString("missing_key");
+    if (missing_key == NULL) {
+        goto error;
+    }
+
+    value = PyUnicode_FromString("value");
+    if (value == NULL) {
+        goto error;
+    }
+
+    // test PyDict_SetItem()
+    Py_ssize_t key_refcnt = Py_REFCNT(key);
+    Py_ssize_t value_refcnt = Py_REFCNT(value);
+    res = PyDict_SetItem(dict, key, value);
+    if (res < 0) {
+        goto error;
+    }
+    assert(res == 0);
+    assert(Py_REFCNT(key) == (key_refcnt + 1));
+    assert(Py_REFCNT(value) == (value_refcnt + 1));
+
+    // test PyDict_SetItemString()
+    res = PyDict_SetItemString(dict, "key", value);
+    if (res < 0) {
+        goto error;
+    }
+    assert(res == 0);
+    assert(Py_REFCNT(key) == (key_refcnt + 1));
+    assert(Py_REFCNT(value) == (value_refcnt + 1));
+
+    // test PyDict_Size()
+    assert(PyDict_Size(dict) == 1);
+
+    // test PyDict_Contains(), key is present
+    assert(PyDict_Contains(dict, key) == 1);
+
+    // test PyDict_GetItem(), key is present
+    assert(PyDict_GetItem(dict, key) == value);
+
+    // test PyDict_GetItemString(), key is present
+    assert(PyDict_GetItemString(dict, "key") == value);
+
+    // test PyDict_GetItemWithError(), key is present
+    assert(PyDict_GetItemWithError(dict, key) == value);
+    assert(!PyErr_Occurred());
+
+    // test PyDict_GetItemRef(), key is present
+    PyObject *get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemRef(dict, key, &get_value) == 1);
+    assert(get_value == value);
+    Py_DECREF(get_value);
+
+    // test PyDict_GetItemStringRef(), key is present
+    get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemStringRef(dict, "key", &get_value) == 1);
+    assert(get_value == value);
+    Py_DECREF(get_value);
+
+    // test PyDict_Contains(), missing key
+    assert(PyDict_Contains(dict, missing_key) == 0);
+
+    // test PyDict_GetItem(), missing key
+    assert(PyDict_GetItem(dict, missing_key) == NULL);
+    assert(!PyErr_Occurred());
+
+    // test PyDict_GetItemString(), missing key
+    assert(PyDict_GetItemString(dict, "missing_key") == NULL);
+    assert(!PyErr_Occurred());
+
+    // test PyDict_GetItemWithError(), missing key
+    assert(PyDict_GetItem(dict, missing_key) == NULL);
+    assert(!PyErr_Occurred());
+
+    // test PyDict_GetItemRef(), missing key
+    get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemRef(dict, missing_key, &get_value) == 0);
+    assert(!PyErr_Occurred());
+    assert(get_value == NULL);
+
+    // test PyDict_GetItemStringRef(), missing key
+    get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemStringRef(dict, "missing_key", &get_value) == 0);
+    assert(!PyErr_Occurred());
+    assert(get_value == NULL);
+
+    // test PyDict_GetItem(), invalid dict
+    PyObject *invalid_dict = key;  // borrowed reference
+    assert(PyDict_GetItem(invalid_dict, key) == NULL);
+    assert(!PyErr_Occurred());
+
+    // test PyDict_GetItemWithError(), invalid dict
+    assert(PyDict_GetItemWithError(invalid_dict, key) == NULL);
+    assert(PyErr_ExceptionMatches(PyExc_SystemError));
+    PyErr_Clear();
+
+    // test PyDict_GetItemRef(), invalid dict
+    get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemRef(invalid_dict, key, &get_value) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_SystemError));
+    PyErr_Clear();
+    assert(get_value == NULL);
+
+    // test PyDict_GetItemStringRef(), invalid dict
+    get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemStringRef(invalid_dict, "key", &get_value) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_SystemError));
+    PyErr_Clear();
+    assert(get_value == NULL);
+
+    invalid_key = PyList_New(0);
+    if (invalid_key == NULL) {
+        goto error;
+    }
+
+    // test PyDict_Contains(), invalid key
+    assert(PyDict_Contains(dict, invalid_key) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_TypeError));
+    PyErr_Clear();
+
+    // test PyDict_GetItem(), invalid key
+    assert(PyDict_GetItem(dict, invalid_key) == NULL);
+    assert(!PyErr_Occurred());
+
+    // test PyDict_GetItemWithError(), invalid key
+    assert(PyDict_GetItemWithError(dict, invalid_key) == NULL);
+    assert(PyErr_ExceptionMatches(PyExc_TypeError));
+    PyErr_Clear();
+
+    // test PyDict_GetItemRef(), invalid key
+    get_value = Py_Ellipsis;  // marker value
+    assert(PyDict_GetItemRef(dict, invalid_key, &get_value) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_TypeError));
+    PyErr_Clear();
+    assert(get_value == NULL);
+
+    // test PyDict_DelItem(), key is present
+    assert(PyDict_DelItem(dict, key) == 0);
+    assert(PyDict_Size(dict) == 0);
+
+    // test PyDict_DelItem(), missing key
+    assert(PyDict_DelItem(dict, missing_key) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_KeyError));
+    PyErr_Clear();
+
+    // test PyDict_DelItem(), invalid key
+    assert(PyDict_DelItem(dict, invalid_key) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_TypeError));
+    PyErr_Clear();
+
+    // test PyDict_Clear()
+    PyDict_Clear(dict);
+
+    Py_DECREF(dict);
+    Py_DECREF(key);
+    Py_DECREF(missing_key);
+    Py_DECREF(value);
+    Py_DECREF(invalid_key);
+
+    Py_RETURN_NONE;
+
+error:
+    Py_XDECREF(dict);
+    Py_XDECREF(key);
+    Py_XDECREF(missing_key);
+    Py_XDECREF(value);
+    Py_XDECREF(invalid_key);
+    return NULL;
+}
+
+
 static PyMethodDef TestMethods[] = {
     {"set_errno",               set_errno,                       METH_VARARGS},
     {"test_config",             test_config,                     METH_NOARGS},
@@ -3609,6 +3799,7 @@ static PyMethodDef TestMethods[] = {
     {"function_set_kw_defaults", function_set_kw_defaults, METH_VARARGS, NULL},
     {"check_pyimport_addmodule", check_pyimport_addmodule, METH_VARARGS},
     {"test_weakref_capi", test_weakref_capi, METH_NOARGS},
+    {"test_dict_capi", test_dict_capi, METH_NOARGS},
     {NULL, NULL} /* sentinel */
 };