gh-112068: C API: Add support of nullable arguments in PyArg_Parse (GH-121303)

serhiy-storchaka · web-flow · commit f5f1ac84b3b9 · 2025-04-08T22:08:00.000+03:00
diff --git a/Doc/c-api/arg.rst b/Doc/c-api/arg.rst
@@ -113,14 +113,18 @@ There are three ways strings and buffers can be converted to C:
 ``z`` (:class:`str` or ``None``) [const char \*]
    Like ``s``, but the Python object may also be ``None``, in which case the C
    pointer is set to ``NULL``.
+   It is the same as ``s?`` with the C pointer was initialized to ``NULL``.
 
 ``z*`` (:class:`str`, :term:`bytes-like object` or ``None``) [Py_buffer]
    Like ``s*``, but the Python object may also be ``None``, in which case the
    ``buf`` member of the :c:type:`Py_buffer` structure is set to ``NULL``.
+   It is the same as ``s*?`` with the ``buf`` member of the :c:type:`Py_buffer`
+   structure was initialized to ``NULL``.
 
 ``z#`` (:class:`str`, read-only :term:`bytes-like object` or ``None``) [const char \*, :c:type:`Py_ssize_t`]
    Like ``s#``, but the Python object may also be ``None``, in which case the C
    pointer is set to ``NULL``.
+   It is the same as ``s#?`` with the C pointer was initialized to ``NULL``.
 
 ``y`` (read-only :term:`bytes-like object`) [const char \*]
    This format converts a bytes-like object to a C pointer to a
@@ -377,6 +381,17 @@ Other objects
       Non-tuple sequences are deprecated if *items* contains format units
       which store a borrowed buffer or a borrowed reference.
 
+``unit?`` (anything or ``None``) [*matching-variable(s)*]
+   ``?`` modifies the behavior of the preceding format unit.
+   The C variable(s) corresponding to that parameter should be initialized
+   to their default value --- when the argument is ``None``,
+   :c:func:`PyArg_ParseTuple` does not touch the contents of the corresponding
+   C variable(s).
+   If the argument is not ``None``, it is parsed according to the specified
+   format unit.
+
+   .. versionadded:: next
+
 A few other characters have a meaning in a format string.  These may not occur
 inside nested parentheses.  They are:
 
diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
@@ -1846,6 +1846,11 @@ New features
   file.
   (Contributed by Victor Stinner in :gh:`127350`.)
 
+* Add support of nullable arguments in :c:func:`PyArg_ParseTuple` and
+  similar functions.
+  Adding ``?`` after any format unit makes ``None`` be accepted as a value.
+  (Contributed by Serhiy Storchaka in :gh:`112068`.)
+
 * Add macros :c:func:`Py_PACK_VERSION` and :c:func:`Py_PACK_FULL_VERSION` for
   bit-packing Python version numbers.
   (Contributed by Petr Viktorin in :gh:`128629`.)
diff --git a/Lib/test/test_capi/test_getargs.py b/Lib/test/test_capi/test_getargs.py
@@ -1387,6 +1387,123 @@ def test_nested_sequence(self):
                     "argument 1 must be sequence of length 1, not 0"):
                 parse(([],), {}, '(' + f + ')', ['a'])
 
+    def test_specific_type_errors(self):
+        parse = _testcapi.parse_tuple_and_keywords
+
+        def check(format, arg, expected, got='list'):
+            errmsg = f'must be {expected}, not {got}'
+            with self.assertRaisesRegex(TypeError, errmsg):
+                parse((arg,), {}, format, ['a'])
+
+        check('k', [], 'int')
+        check('k?', [], 'int or None')
+        check('K', [], 'int')
+        check('K?', [], 'int or None')
+        check('c', [], 'a byte string of length 1')
+        check('c?', [], 'a byte string of length 1 or None')
+        check('c', b'abc', 'a byte string of length 1',
+              'a bytes object of length 3')
+        check('c?', b'abc', 'a byte string of length 1 or None',
+              'a bytes object of length 3')
+        check('c', bytearray(b'abc'), 'a byte string of length 1',
+              'a bytearray object of length 3')
+        check('c?', bytearray(b'abc'), 'a byte string of length 1 or None',
+              'a bytearray object of length 3')
+        check('C', [], 'a unicode character')
+        check('C?', [], 'a unicode character or None')
+        check('C', 'abc', 'a unicode character',
+              'a string of length 3')
+        check('C?', 'abc', 'a unicode character or None',
+              'a string of length 3')
+        check('s', [], 'str')
+        check('s?', [], 'str or None')
+        check('z', [], 'str or None')
+        check('z?', [], 'str or None')
+        check('es', [], 'str')
+        check('es?', [], 'str or None')
+        check('es#', [], 'str')
+        check('es#?', [], 'str or None')
+        check('et', [], 'str, bytes or bytearray')
+        check('et?', [], 'str, bytes, bytearray or None')
+        check('et#', [], 'str, bytes or bytearray')
+        check('et#?', [], 'str, bytes, bytearray or None')
+        check('w*', [], 'read-write bytes-like object')
+        check('w*?', [], 'read-write bytes-like object or None')
+        check('S', [], 'bytes')
+        check('S?', [], 'bytes or None')
+        check('U', [], 'str')
+        check('U?', [], 'str or None')
+        check('Y', [], 'bytearray')
+        check('Y?', [], 'bytearray or None')
+        check('(OO)', 42, '2-item tuple', 'int')
+        check('(OO)?', 42, '2-item tuple or None', 'int')
+        check('(OO)', (1, 2, 3), 'tuple of length 2', '3')
+
+    def test_nullable(self):
+        parse = _testcapi.parse_tuple_and_keywords
+
+        def check(format, arg, allows_none=False):
+            # Because some format units (such as y*) require cleanup,
+            # we force the parsing code to perform the cleanup by adding
+            # an argument that always fails.
+            # By checking for an exception, we ensure that the parsing
+            # of the first argument was successful.
+            self.assertRaises(OverflowError, parse,
+                              (arg, 256), {}, format + '?b', ['a', 'b'])
+            self.assertRaises(OverflowError, parse,
+                              (None, 256), {}, format + '?b', ['a', 'b'])
+            self.assertRaises(OverflowError, parse,
+                              (arg, 256), {}, format + 'b', ['a', 'b'])
+            self.assertRaises(OverflowError if allows_none else TypeError, parse,
+                              (None, 256), {}, format + 'b', ['a', 'b'])
+
+        check('b', 42)
+        check('B', 42)
+        check('h', 42)
+        check('H', 42)
+        check('i', 42)
+        check('I', 42)
+        check('n', 42)
+        check('l', 42)
+        check('k', 42)
+        check('L', 42)
+        check('K', 42)
+        check('f', 2.5)
+        check('d', 2.5)
+        check('D', 2.5j)
+        check('c', b'a')
+        check('C', 'a')
+        check('p', True, allows_none=True)
+        check('y', b'buffer')
+        check('y*', b'buffer')
+        check('y#', b'buffer')
+        check('s', 'string')
+        check('s*', 'string')
+        check('s#', 'string')
+        check('z', 'string', allows_none=True)
+        check('z*', 'string', allows_none=True)
+        check('z#', 'string', allows_none=True)
+        check('w*', bytearray(b'buffer'))
+        check('U', 'string')
+        check('S', b'bytes')
+        check('Y', bytearray(b'bytearray'))
+        check('O', object, allows_none=True)
+
+        check('(OO)', (1, 2))
+        self.assertEqual(parse((((1, 2), 3),), {}, '((OO)?O)', ['a']), (1, 2, 3))
+        self.assertEqual(parse(((None, 3),), {}, '((OO)?O)', ['a']), (NULL, NULL, 3))
+        self.assertEqual(parse((((1, 2), 3),), {}, '((OO)O)', ['a']), (1, 2, 3))
+        self.assertRaises(TypeError, parse, ((None, 3),), {}, '((OO)O)', ['a'])
+
+        parse((None,), {}, 'es?', ['a'])
+        parse((None,), {}, 'es#?', ['a'])
+        parse((None,), {}, 'et?', ['a'])
+        parse((None,), {}, 'et#?', ['a'])
+        parse((None,), {}, 'O!?', ['a'])
+        parse((None,), {}, 'O&?', ['a'])
+
+        # TODO: More tests for es?, es#?, et?, et#?, O!, O&
+
     @unittest.skipIf(_testinternalcapi is None, 'needs _testinternalcapi')
     def test_gh_119213(self):
         rc, out, err = script_helper.assert_python_ok("-c", """if True:
diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
@@ -732,7 +732,7 @@ def test_tagname(self):
         m2.close()
         m1.close()
 
-        with self.assertRaisesRegex(TypeError, 'tagname'):
+        with self.assertRaisesRegex(TypeError, 'must be str or None'):
             mmap.mmap(-1, 8, tagname=1)
 
     @cpython_only
diff --git a/Misc/NEWS.d/next/C_API/2025-01-08-18-55-57.gh-issue-112068.ofI5Fl.rst b/Misc/NEWS.d/next/C_API/2025-01-08-18-55-57.gh-issue-112068.ofI5Fl.rst
@@ -0,0 +1,3 @@
+Add support of nullable arguments in :c:func:`PyArg_Parse` and similar
+functions. Adding ``?`` after any format unit makes ``None`` be accepted as
+a value.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
@@ -3848,9 +3848,7 @@ _validate_paramflags(ctypes_state *st, PyTypeObject *type, PyObject *paramflags)
         PyObject *name = Py_None;
         PyObject *defval;
         PyObject *typ;
-        if (!PyArg_ParseTuple(item, "i|OO", &flag, &name, &defval) ||
-            !(name == Py_None || PyUnicode_Check(name)))
-        {
+        if (!PyArg_ParseTuple(item, "i|U?O", &flag, &name, &defval)) {
             PyErr_SetString(PyExc_TypeError,
                    "paramflags must be a sequence of (int [,string [,value]]) tuples");
             return 0;
@@ -3915,10 +3913,8 @@ PyCFuncPtr_FromDll(PyTypeObject *type, PyObject *args, PyObject *kwds)
     void *handle;
     PyObject *paramflags = NULL;
 
-    if (!PyArg_ParseTuple(args, "O|O", &ftuple, &paramflags))
+    if (!PyArg_ParseTuple(args, "O|O?", &ftuple, &paramflags))
         return NULL;
-    if (paramflags == Py_None)
-        paramflags = NULL;
 
     ftuple = PySequence_Tuple(ftuple);
     if (!ftuple)
@@ -4050,10 +4046,8 @@ PyCFuncPtr_FromVtblIndex(PyTypeObject *type, PyObject *args, PyObject *kwds)
     GUID *iid = NULL;
     Py_ssize_t iid_len = 0;
 
-    if (!PyArg_ParseTuple(args, "is|Oz#", &index, &name, &paramflags, &iid, &iid_len))
+    if (!PyArg_ParseTuple(args, "is|O?z#", &index, &name, &paramflags, &iid, &iid_len))
         return NULL;
-    if (paramflags == Py_None)
-        paramflags = NULL;
 
     ctypes_state *st = get_module_state_by_def(Py_TYPE(type));
     if (!_validate_paramflags(st, type, paramflags)) {
diff --git a/Modules/_interpretersmodule.c b/Modules/_interpretersmodule.c
@@ -1252,14 +1252,11 @@ interp_get_config(PyObject *self, PyObject *args, PyObject *kwds)
     PyObject *idobj = NULL;
     int restricted = 0;
     if (!PyArg_ParseTupleAndKeywords(args, kwds,
-                                     "O|$p:get_config", kwlist,
+                                     "O?|$p:get_config", kwlist,
                                      &idobj, &restricted))
     {
         return NULL;
     }
-    if (idobj == Py_None) {
-        idobj = NULL;
-    }
 
     int reqready = 0;
     PyInterpreterState *interp = \
@@ -1376,14 +1373,14 @@ capture_exception(PyObject *self, PyObject *args, PyObject *kwds)
     static char *kwlist[] = {"exc", NULL};
     PyObject *exc_arg = NULL;
     if (!PyArg_ParseTupleAndKeywords(args, kwds,
-                                     "|O:capture_exception", kwlist,
+                                     "|O?:capture_exception", kwlist,
                                      &exc_arg))
     {
         return NULL;
     }
 
     PyObject *exc = exc_arg;
-    if (exc == NULL || exc == Py_None) {
+    if (exc == NULL) {
         exc = PyErr_GetRaisedException();
         if (exc == NULL) {
             Py_RETURN_NONE;
diff --git a/Modules/_json.c b/Modules/_json.c
@@ -1228,23 +1228,16 @@ encoder_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     static char *kwlist[] = {"markers", "default", "encoder", "indent", "key_separator", "item_separator", "sort_keys", "skipkeys", "allow_nan", NULL};
 
     PyEncoderObject *s;
-    PyObject *markers, *defaultfn, *encoder, *indent, *key_separator;
+    PyObject *markers = Py_None, *defaultfn, *encoder, *indent, *key_separator;
     PyObject *item_separator;
     int sort_keys, skipkeys, allow_nan;
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "OOOOUUppp:make_encoder", kwlist,
-        &markers, &defaultfn, &encoder, &indent,
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!?OOOUUppp:make_encoder", kwlist,
+        &PyDict_Type, &markers, &defaultfn, &encoder, &indent,
         &key_separator, &item_separator,
         &sort_keys, &skipkeys, &allow_nan))
         return NULL;
 
-    if (markers != Py_None && !PyDict_Check(markers)) {
-        PyErr_Format(PyExc_TypeError,
-                     "make_encoder() argument 1 must be dict or None, "
-                     "not %.200s", Py_TYPE(markers)->tp_name);
-        return NULL;
-    }
-
     s = (PyEncoderObject *)type->tp_alloc(type, 0);
     if (s == NULL)
         return NULL;
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
@@ -651,12 +651,12 @@ PyThreadHandleObject_join(PyObject *op, PyObject *args)
     PyThreadHandleObject *self = PyThreadHandleObject_CAST(op);
 
     PyObject *timeout_obj = NULL;
-    if (!PyArg_ParseTuple(args, "|O:join", &timeout_obj)) {
+    if (!PyArg_ParseTuple(args, "|O?:join", &timeout_obj)) {
         return NULL;
     }
 
     PyTime_t timeout_ns = -1;
-    if (timeout_obj != NULL && timeout_obj != Py_None) {
+    if (timeout_obj != NULL) {
         if (_PyTime_FromSecondsObject(&timeout_ns, timeout_obj,
                                       _PyTime_ROUND_TIMEOUT) < 0) {
             return NULL;
@@ -1919,10 +1919,10 @@ thread_PyThread_start_joinable_thread(PyObject *module, PyObject *fargs,
     PyObject *func = NULL;
     int daemon = 1;
     thread_module_state *state = get_thread_state(module);
-    PyObject *hobj = NULL;
+    PyObject *hobj = Py_None;
     if (!PyArg_ParseTupleAndKeywords(fargs, fkwargs,
-                                     "O|Op:start_joinable_thread", keywords,
-                                     &func, &hobj, &daemon)) {
+                                     "O|O!?p:start_joinable_thread", keywords,
+                                     &func, state->thread_handle_type, &hobj, &daemon)) {
         return NULL;
     }
 
@@ -1932,14 +1932,6 @@ thread_PyThread_start_joinable_thread(PyObject *module, PyObject *fargs,
         return NULL;
     }
 
-    if (hobj == NULL) {
-        hobj = Py_None;
-    }
-    else if (hobj != Py_None && !Py_IS_TYPE(hobj, state->thread_handle_type)) {
-        PyErr_SetString(PyExc_TypeError, "'handle' must be a _ThreadHandle");
-        return NULL;
-    }
-
     if (PySys_Audit("_thread.start_joinable_thread", "OiO", func, daemon,
                     hobj) < 0) {
         return NULL;
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
@@ -23,7 +23,6 @@
 #endif
 
 #include <Python.h>
-#include "pycore_abstract.h"      // _Py_convert_optional_to_ssize_t()
 #include "pycore_bytesobject.h"   // _PyBytes_Find()
 #include "pycore_fileutils.h"     // _Py_stat_struct
 
@@ -516,7 +515,7 @@ mmap_read_method(PyObject *op, PyObject *args)
     mmap_object *self = mmap_object_CAST(op);
 
     CHECK_VALID(NULL);
-    if (!PyArg_ParseTuple(args, "|O&:read", _Py_convert_optional_to_ssize_t, &num_bytes))
+    if (!PyArg_ParseTuple(args, "|n?:read", &num_bytes))
         return NULL;
     CHECK_VALID(NULL);
 
@@ -1710,7 +1709,7 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
     DWORD off_lo;       /* lower 32 bits of offset */
     DWORD size_hi;      /* upper 32 bits of size */
     DWORD size_lo;      /* lower 32 bits of size */
-    PyObject *tagname = Py_None;
+    PyObject *tagname = NULL;
     DWORD dwErr = 0;
     int fileno;
     HANDLE fh = 0;
@@ -1720,7 +1719,7 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
                                 "tagname",
                                 "access", "offset", NULL };
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwdict, "in|OiL", keywords,
+    if (!PyArg_ParseTupleAndKeywords(args, kwdict, "in|U?iL", keywords,
                                      &fileno, &map_size,
                                      &tagname, &access, &offset)) {
         return NULL;
@@ -1853,13 +1852,7 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
     m_obj->weakreflist = NULL;
     m_obj->exports = 0;
     /* set the tag name */
-    if (!Py_IsNone(tagname)) {
-        if (!PyUnicode_Check(tagname)) {
-            Py_DECREF(m_obj);
-            return PyErr_Format(PyExc_TypeError, "expected str or None for "
-                                "'tagname', not %.200s",
-                                Py_TYPE(tagname)->tp_name);
-        }
+    if (tagname != NULL) {
         m_obj->tagname = PyUnicode_AsWideCharString(tagname, NULL);
         if (m_obj->tagname == NULL) {
             Py_DECREF(m_obj);
diff --git a/Python/getargs.c b/Python/getargs.c
