gh-129068: allow concurrent iteration over range iterators

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`.)

Include/internal/pycore_range.h

@@ -10,11 +10,26 @@ extern "C" {
 
 typedef struct {
     PyObject_HEAD
-    long start;
-    long step;
     long len;
+    long end;
+    long step;
+    long stop;
 } _PyRangeIterObject;
 
+static inline long
+_PyRangeIter_GetLengthAndStart(_PyRangeIterObject *r, long *value)
+{
+    long len = FT_ATOMIC_LOAD_LONG_RELAXED(r->len);
+    *value = r->end - r->step * len;
+    return len;
+}
+
+static inline void
+_PyRangeIter_SetLength(_PyRangeIterObject *r, long len)
+{
+    FT_ATOMIC_STORE_LONG_RELAXED(r->len, len);
+}
+
 #ifdef __cplusplus
 }
 #endif