gh-50333: Deprecate support of non-tuple sequences in PyArg_ParseTuple() (GH-128374)

Non-tuple sequences are deprecated as argument for the "(items)" format unit
in PyArg_ParseTuple() and other argument parsing functions if items contains
format units which store borrowed buffer or reference (e.g. "s" and "O").

str and bytearray are no longer accepted as valid sequences.

Author: serhiy-storchaka

Doc/c-api/arg.rst

@@ -357,11 +357,26 @@ Other objects
 
    .. versionadded:: 3.3
 
-``(items)`` (:class:`tuple`) [*matching-items*]
-   The object must be a Python sequence whose length is the number of format units
+``(items)`` (sequence) [*matching-items*]
+   The object must be a Python sequence (except :class:`str`, :class:`bytes`
+   or :class:`bytearray`) whose length is the number of format units
    in *items*.  The C arguments must correspond to the individual format units in
    *items*.  Format units for sequences may be nested.
 
+   If *items* contains format units which store a :ref:`borrowed buffer
+   <c-arg-borrowed-buffer>` (``s``, ``s#``, ``z``, ``z#``, ``y``, or ``y#``)
+   or a :term:`borrowed reference` (``S``, ``Y``, ``U``, ``O``, or ``O!``),
+   the object must be a Python tuple.
+   The *converter* for the ``O&`` format unit in *items* must not store
+   a borrowed buffer or a borrowed reference.
+
+   .. versionchanged:: next
+      :class:`str` and :class:`bytearray` objects no longer accepted as a sequence.
+
+   .. deprecated:: next
+      Non-tuple sequences are deprecated if *items* contains format units
+      which store a borrowed buffer or a borrowed reference.
+
 A few other characters have a meaning in a format string.  These may not occur
 inside nested parentheses.  They are:
 

Doc/whatsnew/3.14.rst

@@ -1938,6 +1938,13 @@ Deprecated
   :c:macro:`!isfinite` available from :file:`math.h`
   since C99.  (Contributed by Sergey B Kirpichev in :gh:`119613`.)
 
+* Non-tuple sequences are deprecated as argument for the ``(items)``
+  format unit in :c:func:`PyArg_ParseTuple` and other
+  :ref:`argument parsing <arg-parsing>` functions if *items* contains
+  format units which store a :ref:`borrowed buffer <c-arg-borrowed-buffer>`
+  or a :term:`borrowed reference`.
+  (Contributed by Serhiy Storchaka in :gh:`50333`.)
+
 * The previously undocumented function :c:func:`PySequence_In` is :term:`soft deprecated`.
   Use :c:func:`PySequence_Contains` instead.
   (Contributed by Yuki Kobayashi in :gh:`127896`.)

Lib/test/test_capi/test_getargs.py

@@ -63,6 +63,9 @@
 
 NULL = None
 
+class CustomError(Exception):
+    pass
+
 class Index:
     def __index__(self):
         return 99
@@ -586,13 +589,13 @@ def test_tuple(self):
         ret = getargs_tuple(1, (2, 3))
         self.assertEqual(ret, (1,2,3))
 
-        # make sure invalid tuple arguments are handled correctly
-        class seq:
+        # make sure invalid sequence arguments are handled correctly
+        class TestSeq:
             def __len__(self):
                 return 2
             def __getitem__(self, n):
-                raise ValueError
-        self.assertRaises(TypeError, getargs_tuple, 1, seq())
+                raise CustomError
+        self.assertRaises(CustomError, getargs_tuple, 1, TestSeq())
 
 class Keywords_TestCase(unittest.TestCase):
     def test_kwargs(self):
@@ -1320,33 +1323,69 @@ def test_nonascii_keywords(self):
                             f"this function got an unexpected keyword argument '{name2}'"):
                         parse((), {name2: 1, name3: 2}, '|OO', [name, name3])
 
-    def test_nested_tuple(self):
+    def test_nested_sequence(self):
         parse = _testcapi.parse_tuple_and_keywords
 
         self.assertEqual(parse(((1, 2, 3),), {}, '(OOO)', ['a']), (1, 2, 3))
         self.assertEqual(parse((1, (2, 3), 4), {}, 'O(OO)O', ['a', 'b', 'c']),
                          (1, 2, 3, 4))
         parse(((1, 2, 3),), {}, '(iii)', ['a'])
+        parse(([1, 2, 3],), {}, '(iii)', ['a'])
 
         with self.assertRaisesRegex(TypeError,
-                "argument 1 must be sequence of length 2, not 3"):
+                "argument 1 must be tuple of length 2, not 3"):
             parse(((1, 2, 3),), {}, '(ii)', ['a'])
         with self.assertRaisesRegex(TypeError,
-                "argument 1 must be sequence of length 2, not 1"):
+                "argument 1 must be tuple of length 2, not 1"):
             parse(((1,),), {}, '(ii)', ['a'])
         with self.assertRaisesRegex(TypeError,
-                "argument 1 must be 2-item sequence, not int"):
+                "argument 1 must be sequence of length 2, not 3"):
+            parse(([1, 2, 3],), {}, '(ii)', ['a'])
+        with self.assertRaisesRegex(TypeError,
+                "argument 1 must be sequence of length 2, not 1"):
+            parse(([1,],), {}, '(ii)', ['a'])
+        with self.assertRaisesRegex(TypeError,
+                "argument 1 must be 2-item tuple, not int"):
             parse((1,), {}, '(ii)', ['a'])
         with self.assertRaisesRegex(TypeError,
-                "argument 1 must be 2-item sequence, not bytes"):
+                "argument 1 must be 2-item tuple, not None$"):
+            parse((None,), {}, '(ii)', ['a'])
+        with self.assertRaisesRegex(TypeError,
+                "argument 1 must be 2-item tuple, not str"):
+            parse(('ab',), {}, '(CC)', ['a'])
+        with self.assertRaisesRegex(TypeError,
+                "argument 1 must be 2-item tuple, not bytes"):
             parse((b'ab',), {}, '(ii)', ['a'])
+        with self.assertRaisesRegex(TypeError,
+                "argument 1 must be 2-item tuple, not bytearray"):
+            parse((bytearray(b'ab'),), {}, '(ii)', ['a'])
+        with self.assertRaisesRegex(TypeError,
+                "argument 1 must be 2-item tuple, not dict"):
+            parse(({},), {}, '(ii)', ['a'])
+
+        with self.assertWarnsRegex(DeprecationWarning,
+                "argument must be 3-item tuple, not list"):
+            self.assertEqual(parse(([1, 2, 3],), {}, '(OOO)', ['a']), (1, 2, 3))
+        with self.assertWarnsRegex(DeprecationWarning,
+                "argument must be 2-item tuple, not list"):
+            with self.assertRaisesRegex(TypeError,
+                    "argument 1 must be tuple of length 2, not 3"):
+                parse(([1, 2, 3],), {}, '(OO)', ['a'])
+        with self.assertWarnsRegex(DeprecationWarning,
+                "argument must be 2-item tuple, not list"):
+            with self.assertRaisesRegex(TypeError,
+                    "argument 1 must be tuple of length 2, not 1"):
+                parse(([1,],), {}, '(OO)', ['a'])
 
         for f in 'es', 'et', 'es#', 'et#':
             with self.assertRaises(LookupError):  # empty encoding ""
                 parse((('a',),), {}, '(' + f + ')', ['a'])
             with self.assertRaisesRegex(TypeError,
-                    "argument 1 must be sequence of length 1, not 0"):
+                    "argument 1 must be tuple of length 1, not 0"):
                 parse(((),), {}, '(' + f + ')', ['a'])
+            with self.assertRaisesRegex(TypeError,
+                    "argument 1 must be sequence of length 1, not 0"):
+                parse(([],), {}, '(' + f + ')', ['a'])
 
     @unittest.skipIf(_testinternalcapi is None, 'needs _testinternalcapi')
     def test_gh_119213(self):

Misc/NEWS.d/next/C_API/2024-12-31-15-28-14.gh-issue-50333.KxQUXa.rst

@@ -0,0 +1,5 @@
+Non-tuple sequences are deprecated as argument for the ``(items)`` format
+unit in :c:func:`PyArg_ParseTuple` and other :ref:`argument parsing
+<arg-parsing>` functions if *items* contains format units which store
+a :ref:`borrowed buffer <c-arg-borrowed-buffer>` or
+a :term:`borrowed reference`.

Python/getargs.c

@@ -466,6 +466,8 @@ converttuple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
     const char *format = *p_format;
     int i;
     Py_ssize_t len;
+    int istuple = PyTuple_Check(arg);
+    int mustbetuple = istuple;
 
     for (;;) {
         int c = *format++;
@@ -481,51 +483,104 @@ converttuple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
         }
         else if (c == ':' || c == ';' || c == '\0')
             break;
-        else if (level == 0 && Py_ISALPHA(c) && c != 'e')
-            n++;
+        else {
+            if (level == 0 && Py_ISALPHA(c)) {
+                n++;
+            }
+            if (c == 'e' && (*format == 's' || *format == 't')) {
+                format++;
+                continue;
+            }
+            if (!mustbetuple) {
+                switch (c) {
+                    case 'y':
+                    case 's':
+                    case 'z':
+                        if (*format != '*') {
+                            mustbetuple = 1;
+                        }
+                        break;
+                    case 'S':
+                    case 'Y':
+                    case 'U':
+                        mustbetuple = 1;
+                        break;
+                    case 'O':
+                        if (*format != '&') {
+                            mustbetuple = 1;
+                        }
+                        break;
+                }
+            }
+        }
     }
 
-    if (!PySequence_Check(arg) || PyBytes_Check(arg)) {
+    if (istuple) {
+        /* fallthrough */
+    }
+    else if (!PySequence_Check(arg) ||
+        PyUnicode_Check(arg) || PyBytes_Check(arg) || PyByteArray_Check(arg))
+    {
         levels[0] = 0;
         PyOS_snprintf(msgbuf, bufsize,
-                      "must be %d-item sequence, not %.50s",
+                      "must be %d-item tuple, not %.50s",
                   n,
                   arg == Py_None ? "None" : Py_TYPE(arg)->tp_name);
         return msgbuf;
     }
+    else {
+        if (mustbetuple) {
+            if (PyErr_WarnFormat(PyExc_DeprecationWarning, 0,
+                    "argument must be %d-item tuple, not %T", n, arg))
+            {
+                return msgbuf;
+            }
+        }
+        len = PySequence_Size(arg);
+        if (len != n) {
+            levels[0] = 0;
+            PyOS_snprintf(msgbuf, bufsize,
+                          "must be %s of length %d, not %zd",
+                          mustbetuple ? "tuple" : "sequence", n, len);
+            return msgbuf;
+        }
+        arg = PySequence_Tuple(arg);
+        if (arg == NULL) {
+            return msgbuf;
+        }
+    }
 
-    len = PySequence_Size(arg);
+    len = PyTuple_GET_SIZE(arg);
     if (len != n) {
         levels[0] = 0;
         PyOS_snprintf(msgbuf, bufsize,
-                      "must be sequence of length %d, not %zd",
+                      "must be tuple of length %d, not %zd",
                       n, len);
+        if (!istuple) {
+            Py_DECREF(arg);
+        }
         return msgbuf;
     }
 
     format = *p_format;
     for (i = 0; i < n; i++) {
         const char *msg;
-        PyObject *item;
-        item = PySequence_GetItem(arg, i);
-        if (item == NULL) {
-            PyErr_Clear();
-            levels[0] = i+1;
-            levels[1] = 0;
-            strncpy(msgbuf, "is not retrievable", bufsize);
-            return msgbuf;
-        }
+        PyObject *item = PyTuple_GET_ITEM(arg, i);
         msg = convertitem(item, &format, p_va, flags, levels+1,
                           msgbuf, bufsize, freelist);
-        /* PySequence_GetItem calls tp->sq_item, which INCREFs */
-        Py_XDECREF(item);
         if (msg != NULL) {
             levels[0] = i+1;
+            if (!istuple) {
+                Py_DECREF(arg);
+            }
             return msg;
         }
     }
 
     *p_format = format;
+    if (!istuple) {
+        Py_DECREF(arg);
+    }
     return NULL;
 }