Sync pre-release CPython main branch from GitHub (2026-08-20)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`04242c0`](https://www.github.com/python/cpython/commit/04242c027feeff726acb15b6463422897b489bcf) (committed 2026-08-20 19:24:45+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`bf95881`](https://www.github.com/python/cpython/commit/bf95881b84662d3dcd35143495b9880962164fee) (commit date: 2026-08-19 20:28:43+00:00)
- Imported: (`3.16.0a0`) - [`04242c0`](https://www.github.com/python/cpython/commit/04242c027feeff726acb15b6463422897b489bcf) (commit date: 2026-08-20 19:24:45+00:00)

# Noteworthy file changes

- Test files (2 added)
- Low-signal files (5 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GAvQeh7fKKlvDfsPAESrXTtu_sU9br0LAAAz

Differential Revision: D116894938

fbshipit-source-id: 01e8d19fc5e4199a6d78729c15b52933029fd6c2

Author: generatedunixname1734921407115435

Doc/about.rst

@@ -10,7 +10,7 @@ and now maintained as an independent project.
 .. _reStructuredText: https://docutils.sourceforge.io/rst.html
 .. _Sphinx: https://www.sphinx-doc.org/
 
-.. In the online version of these documents, you can submit comments and suggest
+.. In the online version of this documentation, you can submit comments and suggest
    changes directly on the documentation pages.
 
 Development of the documentation and its toolchain is an entirely volunteer

Doc/c-api/import.rst

@@ -146,7 +146,7 @@ Importing Modules
       alternatives.
 
    .. versionchanged:: 3.15
-      ``__cached__`` is no longer set.
+      The ``__cached__`` attribute is no longer set.
 
 
 .. c:function:: PyObject* PyImport_ExecCodeModuleEx(const char *name, PyObject *co, const char *pathname)
@@ -170,7 +170,7 @@ Importing Modules
       :class:`~importlib.machinery.ModuleSpec` for alternatives.
 
    .. versionchanged:: 3.15
-      ``__cached__`` no longer set.
+      The ``__cached__`` attribute no longer set.
 
 
 .. c:function:: PyObject* PyImport_ExecCodeModuleWithPathnames(const char *name, PyObject *co, const char *pathname, const char *cpathname)

Doc/library/runpy.rst

@@ -97,7 +97,7 @@ The :mod:`!runpy` module provides two functions:
       :class:`~importlib.machinery.ModuleSpec` for alternatives.
 
    .. versionchanged:: 3.15
-      ``__cached__`` is no longer set.
+      The global variable ``__cached__`` is no longer set.
 
 .. function:: run_path(path_name, init_globals=None, run_name=None)
 
@@ -175,7 +175,7 @@ The :mod:`!runpy` module provides two functions:
       ``__package__`` are deprecated.
 
    .. versionchanged:: 3.15
-      ``__cached__`` is no longer set.
+      The global variable ``__cached__`` is no longer set.
 
 .. seealso::
 

Doc/reference/datamodel.rst

@@ -1099,14 +1099,9 @@ this approach.
    :ref:`import system <importsystem>` may opt to leave it unset if it
    has no semantic meaning (for example, a module loaded from a database).
 
-   .. deprecated-removed:: 3.13 3.15
-      Setting ``__cached__`` on a module while failing to set
-      :attr:`!__spec__.cached` is deprecated. In Python 3.15,
-      ``__cached__`` will cease to be set or taken into consideration by
-      the import system or standard library.
-
-   .. versionchanged:: 3.15
-      ``__cached__`` is no longer set.
+.. versionchanged:: 3.15
+   The ``__cached__`` attribute is no longer set on modules or taken into
+   consideration by the import system or standard library.
 
 Other writable attributes on module objects
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Doc/tools/templates/indexsidebar.html

@@ -1,5 +1,5 @@
 <h3>{% trans %}Download{% endtrans %}</h3>
-<p><a href="{{ pathto('download') }}">{% trans %}Download these documents{% endtrans %}</a></p>
+<p><a href="{{ pathto('download') }}">{% trans %}Download the documentation{% endtrans %}</a></p>
 <h3>{% trans %}Docs by version{% endtrans %}</h3>
 <ul>
   {# _docs_by_version.html is overwritten by build_docs.py for non-EOL versions #}

Doc/tutorial/stdlib.rst

@@ -36,7 +36,7 @@ aids for working with large modules like :mod:`os`::
    <returns an extensive manual page created from the module's docstrings>
 
 For daily file and directory management tasks, the :mod:`shutil` module provides
-a higher level interface that is easier to use::
+a higher-level interface that is easier to use::
 
    >>> import shutil
    >>> shutil.copyfile('data.db', 'archive.db')
@@ -63,7 +63,7 @@ wildcard searches::
 Command-line arguments
 ======================
 
-Common utility scripts often need to process command line arguments. These
+Common utility scripts often need to process command-line arguments. These
 arguments are stored in the :mod:`sys` module's *argv* attribute as a list.  For
 instance, let's take the following :file:`demo.py` file::
 
@@ -77,7 +77,7 @@ line::
    ['demo.py', 'one', 'two', 'three']
 
 The :mod:`argparse` module provides a more sophisticated mechanism to process
-command line arguments.  The following script extracts one or more filenames
+command-line arguments.  The following script extracts one or more filenames
 and an optional number of lines to be displayed::
 
     import argparse

Doc/whatsnew/3.15.rst

@@ -880,6 +880,14 @@ Other language changes
   other, as regular dynamic extensions do.
   (Contributed by Stefano Rivera in :gh:`122931`.)
 
+* The ``__cached__`` attribute on modules, which was deprecated since version
+  3.13, is no longer set or taken into consideration by the import system or
+  standard library.
+  Use :attr:`__spec__.cached <importlib.machinery.ModuleSpec.cached>` instead.
+  (Contributed by Brett Cannon in :gh:`97879`)
+
+  Note that the :attr:`~module.__loader__` and :attr:`~module.__package__`
+  attributes are also deprecated and scheduled for removal.
 
 
 Default interactive shell

Lib/test/test_curses.py

@@ -895,6 +895,21 @@ def test_output_string_embedded_null_chars(self):
                 self.assertRaises(ValueError, stdscr.insstr, arg)
                 self.assertRaises(ValueError, stdscr.insnstr, arg, 1)
 
+    def test_output_string_attr_restored(self):
+        # A write with an attr restores the window rendition afterwards,
+        # whether it succeeded or failed.
+        win = curses.newwin(2, 10, 0, 0)
+        for func, args in [(win.addstr, ('x',)), (win.addnstr, ('x', 1)),
+                           (win.insstr, ('x',)), (win.insnstr, ('x', 1))]:
+            with self.subTest(func.__qualname__):
+                win.attrset(curses.A_UNDERLINE)
+                # y=100 is outside the window, so the write fails.
+                self.assertRaises(curses.error, func, 100, 0, *args,
+                                  curses.A_BOLD)
+                self.assertEqual(win.getattrs(), curses.A_UNDERLINE)
+                func(0, 0, *args, curses.A_BOLD)
+                self.assertEqual(win.getattrs(), curses.A_UNDERLINE)
+
     def test_add_string_behavior(self):
         # addstr() advances the cursor past the written text; addnstr()
         # writes at most n characters.

Lib/test/test_free_threading/test_gc.py

@@ -2,6 +2,7 @@
 
 import threading
 from threading import Thread
+import time
 from unittest import TestCase
 import gc
 
@@ -94,6 +95,26 @@ def evil():
         thread.start()
         thread.join()
 
+    def test_gc_callbacks_race_with_mutation(self):
+        def collect():
+            b.wait()
+            while not stop.is_set():
+                gc.collect()
+
+        def mutate():
+            b.wait()
+            while not stop.is_set():
+                gc.callbacks[:] = [lambda *_: _ for _ in range(16)]
+                time.sleep(0)
+                gc.callbacks.clear()
+
+        threads = [threading.Thread(target=f) for f in (collect, mutate) * 4]
+        b = threading.Barrier(len(threads) + 1)
+        stop = threading.Event()
+
+        with threading_helper.start_threads(threads, stop.set):
+            b.wait()
+            time.sleep(0.2)
     def test_set_threshold(self):
         # GH-148613: Setting the GC threshold from another thread could cause a
         # race between the `gc_should_collect` and `gc_set_threshold` functions.

Lib/test/test_tools/i18n_data/noheader.pot

@@ -0,0 +1,8 @@
+#: noheader.py:3
+msgid "Foo"
+msgstr ""
+
+#: noheader.py:5
+msgid "Bar"
+msgstr ""
+