gh-139772: Add PyDict_FromItems() function

Author: vstinner

Doc/c-api/dict.rst

@@ -36,6 +36,15 @@ Dictionary Objects
    Return a new empty dictionary, or ``NULL`` on failure.
 
 
+.. c:function:: PyObject* PyDict_FromItems(PyObject *const *keys, PyObject *const *values, Py_ssize_t length)
+
+   Create a dictionary from *keys* and *values* of *length* items.
+
+   Return a new empty dictionary, or ``NULL`` on failure.
+
+   .. versionadded:: next
+
+
 .. c:function:: PyObject* PyDictProxy_New(PyObject *mapping)
 
    Return a :class:`types.MappingProxyType` object for a mapping which

Doc/whatsnew/3.15.rst

@@ -852,6 +852,10 @@ New features
 
   (Contributed by Victor Stinner in :gh:`129813`.)
 
+* Add :c:func:`PyDict_FromItems(keys, values, length) <PyDict_FromItems>`
+  to create a dictionary from *keys* and *values* of *length* items.
+  (Contributed by Victor Stinner in :gh:`139772`.)
+
 * Add :c:func:`PyTuple_FromArray` to create a :class:`tuple` from an array.
   (Contributed by Victor Stinner in :gh:`111489`.)
 

Include/cpython/dictobject.h

@@ -103,3 +103,8 @@ PyAPI_FUNC(int) PyDict_ClearWatcher(int watcher_id);
 // Mark given dictionary as "watched" (callback will be called if it is modified)
 PyAPI_FUNC(int) PyDict_Watch(int watcher_id, PyObject* dict);
 PyAPI_FUNC(int) PyDict_Unwatch(int watcher_id, PyObject* dict);
+
+PyAPI_FUNC(PyObject *) PyDict_FromItems(
+    PyObject *const *keys,
+    PyObject *const *values,
+    Py_ssize_t length);

Lib/test/test_capi/test_dict.py

@@ -545,6 +545,23 @@ def test_dict_popstring(self):
         # CRASHES dict_popstring({}, NULL)
         # CRASHES dict_popstring({"a": 1}, NULL)
 
+    def test_dict_fromitems(self):
+        dict_fromitems = _testcapi.dict_fromitems
+
+        d = dict_fromitems((), ())
+        self.assertEqual(d, {})
+
+        d = dict_fromitems(tuple(range(1, 4)), tuple('abc'))
+        self.assertEqual(d, {1: 'a', 2: 'b', 3: 'c'})
+
+        # test unicode keys
+        d = dict_fromitems(tuple('abc'), tuple(range(1, 4)))
+        self.assertEqual(d, {'a': 1, 'b': 2, 'c': 3})
+
+        # test "large" dict (1024 items)
+        d = dict_fromitems(tuple(range(1024)), tuple(map(str, range(1024))))
+        self.assertEqual(d, {i: str(i) for i in range(1024)})
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/C_API/2025-10-11-18-44-36.gh-issue-139772.GmNHrN.rst

@@ -0,0 +1,3 @@
+Add :c:func:`PyDict_FromItems(keys, values, length) <PyDict_FromItems>` to
+create a dictionary from *keys* and *values* of *length* items. Patch by
+Victor Stinner.

Modules/_testcapi/dict.c

@@ -258,6 +258,29 @@ test_dict_iteration(PyObject* self, PyObject *Py_UNUSED(ignored))
 }
 
 
+static PyObject*
+dict_fromitems(PyObject* self, PyObject *args)
+{
+    PyObject *keys_obj, *values_obj;
+    if (!PyArg_ParseTuple(args, "O!O!",
+                          &PyTuple_Type, &keys_obj,
+                          &PyTuple_Type, &values_obj)) {
+        return NULL;
+    }
+
+    Py_ssize_t length = PyTuple_GET_SIZE(keys_obj);
+    if (PyTuple_GET_SIZE(values_obj) != length) {
+        PyErr_SetString(PyExc_ValueError,
+                        "keys and values must have the same length");
+        return NULL;
+    }
+
+    PyObject **keys = &PyTuple_GET_ITEM(keys_obj, 0);
+    PyObject **values = &PyTuple_GET_ITEM(values_obj, 0);
+    return PyDict_FromItems(keys, values, length);
+}
+
+
 static PyMethodDef test_methods[] = {
     {"dict_containsstring", dict_containsstring, METH_VARARGS},
     {"dict_getitemref", dict_getitemref, METH_VARARGS},
@@ -268,7 +291,8 @@ static PyMethodDef test_methods[] = {
     {"dict_pop_null", dict_pop_null, METH_VARARGS},
     {"dict_popstring", dict_popstring, METH_VARARGS},
     {"dict_popstring_null", dict_popstring_null, METH_VARARGS},
-    {"test_dict_iteration",     test_dict_iteration,             METH_NOARGS},
+    {"test_dict_iteration", test_dict_iteration, METH_NOARGS},
+    {"dict_fromitems", dict_fromitems, METH_VARARGS},
     {NULL},
 };
 

Objects/dictobject.c

@@ -2263,6 +2263,15 @@ _PyDict_FromItems(PyObject *const *keys, Py_ssize_t keys_offset,
     return dict;
 }
 
+
+PyObject *
+PyDict_FromItems(PyObject *const *keys, PyObject *const *values,
+                 Py_ssize_t length)
+{
+    return _PyDict_FromItems(keys, 1, values, 1, length);
+}
+
+
 /* Note that, for historical reasons, PyDict_GetItem() suppresses all errors
  * that may occur (originally dicts supported only string keys, and exceptions
  * weren't possible).  So, while the original intent was that a NULL return