Sync pre-release CPython 3.15 branch from GitHub (2026-06-29)

Summary:
Imported python/cpython `3.15.0b3+dev` from upstream rev [`404113b`](https://www.github.com/python/cpython/commit/404113bd37625215d03545e51f8caa9fb7f1eea8) (committed 2026-06-29 02:34:20+00:00).

# Commit Info

- Base: (`3.15.0b3+dev`) - [`0290166`](https://www.github.com/python/cpython/commit/029016654ec08142f59d4f46113b3c1ec0830387) (commit date: 2026-06-26 23:31:46+00:00)
- Imported: (`3.15.0b3+dev`) - [`404113b`](https://www.github.com/python/cpython/commit/404113bd37625215d03545e51f8caa9fb7f1eea8) (commit date: 2026-06-29 02:34:20+00:00)

# Noteworthy file changes

- Low-signal files (13 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GFSTOyRnpqSSPY8DABLcuAMJrccJbr0LAAAz

Reviewed By: fried

Differential Revision: D110015284

fbshipit-source-id: af9a090a36f40dc0efa3cbdf783f6912668d3650

Author: ambv

Doc/c-api/type.rst

@@ -639,7 +639,7 @@ but need extra remarks for use as slots:
    in the following situations:
 
    - The base is not variable-sized (its
-     :c:member:`~PyTypeObject.tp_itemsize`).
+     :c:member:`~PyTypeObject.tp_itemsize` is zero).
    - The requested :c:member:`PyType_Spec.basicsize` is positive,
      suggesting that the memory layout of the base class is known.
    - The requested :c:member:`PyType_Spec.basicsize` is zero,

Doc/howto/curses.rst

@@ -52,8 +52,8 @@ code, all the functions described here will probably be available.  The older
 versions of curses carried by some proprietary Unixes may not support
 everything, though.
 
-The Windows version of Python doesn't include the :mod:`curses`
-module.  A ported version called :pypi:`UniCurses` is available.
+The Windows version of Python doesn't include the :mod:`curses` module.
+The third-party :pypi:`windows-curses` package provides the same interface on Windows.
 
 
 The Python curses module

Doc/library/curses.rst

@@ -975,6 +975,7 @@ Window objects
 .. method:: window.getbkgd()
 
    Return the given window's current background character/attribute pair.
+   Its components can be extracted like those of :meth:`inch`.
 
 
 .. method:: window.getch([y, x])
@@ -1065,8 +1066,10 @@ Window objects
 
 .. method:: window.inch([y, x])
 
-   Return the character at the given position in the window. The bottom 8 bits are
-   the character proper, and upper bits are the attributes.
+   Return the character at the given position in the window.
+   The bottom 8 bits are the character proper and the upper bits are the attributes;
+   extract them with the :data:`A_CHARTEXT` and :data:`A_ATTRIBUTES` bit-masks,
+   and the color pair with :func:`pair_number`.
 
 
 .. method:: window.insch(ch[, attr])

Doc/library/http.client.rst

@@ -433,6 +433,7 @@ HTTPConnection Objects
 
    The maximum number of allowed response headers to help prevent denial-of-service
    attacks. By default, the maximum number of allowed headers is set to 100.
+   The same limit applies to the trailer section of a chunked response.
 
    .. versionadded:: 3.15
 

Doc/library/itertools.rst

@@ -197,6 +197,10 @@ loops that truncate the stream.
           for iterable in iterables:
               yield from iterable
 
+   Note that :ref:`unpacking in comprehensions <unpacking-comprehensions>`
+   provides similar functionality so that ``list(chain(p, q))`` could be
+   written as ``[*s for s in (p, q)]``.
+
 
 .. classmethod:: chain.from_iterable(iterable)
 
@@ -208,6 +212,10 @@ loops that truncate the stream.
           for iterable in iterables:
               yield from iterable
 
+   Note that :ref:`unpacking in comprehensions <unpacking-comprehensions>`
+   provides similar functionality so that ``list(chain.from_iterable(iterables))``
+   could be written as ``[*s for s in iterables]``.
+
 
 .. function:: combinations(iterable, r)
 

Doc/library/tkinter.messagebox.rst

@@ -113,7 +113,7 @@ Common message box styles and layouts include but are not limited to:
 .. function:: askretrycancel(title=None, message=None, **options)
 
    Ask if operation should be retried. Shows buttons :data:`RETRY` and :data:`CANCEL`.
-   Return ``True`` if the answer is yes and ``False`` otherwise.
+   Return ``True`` if the answer is retry and ``False`` otherwise.
 
 .. function:: askyesno(title=None, message=None, **options)
 

Doc/library/tkinter.rst

@@ -770,6 +770,8 @@ cursor
    The standard X cursor names from :file:`cursorfont.h` can be used, without the
    ``XC_`` prefix.  For example to get a hand cursor (``XC_hand2``), use the
    string ``"hand2"``.  You can also specify a bitmap and mask file of your own.
+   On Windows a cursor file (:file:`.cur` or :file:`.ani`) may be used directly,
+   giving its path preceded with an ``@``, as in ``"@C:/cursors/bart.ani"``.
    See page 179 of Ousterhout's book.
 
 distance
@@ -883,6 +885,20 @@ they are denoted in Tk, which can be useful when referring to the Tk man pages.
 | %d | detail              | %D | delta               |
 +----+---------------------+----+---------------------+
 
+The ``add`` parameter above only affects the bindings you make yourself.
+Every widget also inherits *class bindings*
+that implement its standard behavior --
+for example a :class:`Text` widget binds :kbd:`Control-t`
+to transpose two characters.
+These are described in the bindings section of the widget's Tk man page
+(such as :manpage:`text(3tk)` or :manpage:`entry(3tk)`).
+
+Class bindings are processed separately from your own,
+so binding an event yourself does not replace the default; both run.
+To suppress an unwanted default binding,
+bind the event on the widget
+and return the string ``"break"`` from your callback.
+
 
 The index parameter
 ^^^^^^^^^^^^^^^^^^^

Doc/reference/expressions.rst

@@ -848,6 +848,8 @@ appear directly in a class definition.
    ``yield`` and ``yield from`` prohibited in the implicitly nested scope.
 
 
+.. _unpacking-comprehensions:
+
 Unpacking in comprehensions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

Include/cpython/pystate.h

@@ -143,6 +143,7 @@ struct _ts {
     struct _PyInterpreterFrame *base_frame;
 
     struct _PyInterpreterFrame *last_profiled_frame;
+    uintptr_t last_profiled_frame_seq;
 
     Py_tracefunc c_profilefunc;
     Py_tracefunc c_tracefunc;

Include/internal/pycore_debug_offsets.h

@@ -104,6 +104,7 @@ typedef struct _Py_DebugOffsets {
         uint64_t current_frame;
         uint64_t base_frame;
         uint64_t last_profiled_frame;
+        uint64_t last_profiled_frame_seq;
         uint64_t thread_id;
         uint64_t native_thread_id;
         uint64_t datastack_chunk;
@@ -294,6 +295,7 @@ typedef struct _Py_DebugOffsets {
         .current_frame = offsetof(PyThreadState, current_frame), \
         .base_frame = offsetof(PyThreadState, base_frame), \
         .last_profiled_frame = offsetof(PyThreadState, last_profiled_frame), \
+        .last_profiled_frame_seq = offsetof(PyThreadState, last_profiled_frame_seq), \
         .thread_id = offsetof(PyThreadState, thread_id), \
         .native_thread_id = offsetof(PyThreadState, native_thread_id), \
         .datastack_chunk = offsetof(PyThreadState, datastack_chunk), \