Sync pre-release CPython 3.15 branch from GitHub (2026-07-15)

Summary:
Imported python/cpython `3.15.0b3+dev` from upstream rev [`fd4c7a8`](https://www.github.com/python/cpython/commit/fd4c7a8d4d46c9b7db920a6b766d367ab22e6a1c) (committed 2026-07-15 18:15:24+00:00).

# Commit Info

- Base: (`3.15.0b3+dev`) - [`accfc34`](https://www.github.com/python/cpython/commit/accfc342e792d461eecf6bcbdd242f126822f325) (commit date: 2026-07-15 03:37:16+00:00)
- Imported: (`3.15.0b3+dev`) - [`fd4c7a8`](https://www.github.com/python/cpython/commit/fd4c7a8d4d46c9b7db920a6b766d367ab22e6a1c) (commit date: 2026-07-15 18:15:24+00:00)

# Noteworthy file changes

- Test files (2 added)
- Low-signal files (3 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GOxmXyM1WLxq4yoDAOMZpIIvNw0Fbr0LAAAz

Differential Revision: D112268579

fbshipit-source-id: 89259863e9f676ea44781004760957b20142122a

Author: generatedunixname1734921407115435

Doc/library/stdtypes.rst

@@ -1720,7 +1720,11 @@ category.
 |                          |  :meth:`str.strip`                        |  :meth:`bytes.strip`                              |
 |                          +--------------------+----------------------+----------------------+----------------------------+
 |                          | :meth:`str.lstrip` | :meth:`str.rstrip`   | :meth:`bytes.lstrip` | :meth:`bytes.rstrip`       |
-+--------------------------+--------------------+----------------------+----------------------+----------------------------+
+|                          +--------------------+----------------------+----------------------+----------------------------+
+|                          |  :meth:`str.removeprefix`                 |  :meth:`bytes.removeprefix`                       |
+|                          +-------------------------------------------+---------------------------------------------------+
+|                          |  :meth:`str.removesuffix`                 |  :meth:`bytes.removesuffix`                       |
++--------------------------+-------------------------------------------+---------------------------------------------------+
 | Translation and Encoding |  :meth:`str.translate`                    |  :meth:`bytes.translate`                          |
 |                          +-------------------------------------------+---------------------------------------------------+
 |                          |  :meth:`str.maketrans`                    |  :meth:`bytes.maketrans`                          |

Doc/library/struct.rst

@@ -68,6 +68,7 @@ The module defines the following exception and functions:
    Pack the values *v1*, *v2*, ... according to the format string *format* and
    write the packed bytes into the writable buffer *buffer* starting at
    position *offset*.  Note that *offset* is a required argument.
+   A negative *offset* counts from the end of *buffer*.
 
 
 .. function:: unpack(format, buffer)
@@ -84,6 +85,7 @@ The module defines the following exception and functions:
    string *format*.  The result is a tuple even if it contains exactly one
    item.  The buffer's size in bytes, starting at position *offset*, must be at
    least the size required by the format, as reflected by :func:`calcsize`.
+   A negative *offset* counts from the end of *buffer*.
 
 
 .. function:: iter_unpack(format, buffer)

Doc/library/tkinter.dnd.rst

@@ -16,21 +16,22 @@ a single application, within the same window or between windows. To enable an
 object to be dragged, you must create an event binding for it that starts the
 drag-and-drop process. Typically, you bind a ButtonPress event to a callback
 function that you write (see :ref:`Bindings-and-Events`). The function should
-call :func:`dnd_start`, where 'source' is the object to be dragged, and 'event'
+call :func:`dnd_start`, where *source* is the object to be dragged, and *event*
 is the event that invoked the call (the argument to your callback function).
 
 Selection of a target object occurs as follows:
 
-#. Top-down search of area under mouse for target widget
+#. Top-down search of the area under the mouse for a target widget:
 
- * Target widget should have a callable *dnd_accept* attribute
- * If *dnd_accept* is not present or returns ``None``, search moves to parent widget
- * If no target widget is found, then the target object is ``None``
+   * the target widget should have a callable *dnd_accept* attribute;
+   * if *dnd_accept* is not present or returns ``None``,
+     the search moves to the parent widget;
+   * if no target widget is found, the target object is ``None``.
 
-2. Call to *<old_target>.dnd_leave(source, event)*
-#. Call to *<new_target>.dnd_enter(source, event)*
-#. Call to *<target>.dnd_commit(source, event)* to notify of drop
-#. Call to *<source>.dnd_end(target, event)* to signal end of drag-and-drop
+#. Call to ``<old_target>.dnd_leave(source, event)``.
+#. Call to ``<new_target>.dnd_enter(source, event)``.
+#. Call to ``<target>.dnd_commit(source, event)`` to notify of the drop.
+#. Call to ``<source>.dnd_end(target, event)`` to signal the end of drag-and-drop.
 
 
 .. class:: DndHandler(source, event)