Sync pre-release CPython main branch from GitHub (2026-09-27)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`421c411`](https://www.github.com/python/cpython/commit/421c411672710e29df4c027b6824df17586c9d51) (committed 2026-09-27 04:03:50+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`ee1bbf0`](https://www.github.com/python/cpython/commit/ee1bbf037ff74ff3c5e7b95623d78aa34744cd49) (commit date: 2026-09-26 02:05:24+00:00)
- Imported: (`3.16.0a0`) - [`421c411`](https://www.github.com/python/cpython/commit/421c411672710e29df4c027b6824df17586c9d51) (commit date: 2026-09-27 04:03:50+00:00)

# Noteworthy file changes

- Test files (2 added)
- Low-signal files (8 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GKfbqTB6GlsETeIDAEbVqqEtqdA9br0LAAAz

Differential Revision: D122023959

fbshipit-source-id: 4c123df45309c968f045f86e92d638ec298da8a5

Author: generatedunixname1734921407115435

Doc/conf.py

@@ -469,6 +469,10 @@
 # https://github.com/sphinx-doc/sphinx/issues/12359
 epub_use_index = False
 
+# The default depth of 3 lists over a thousand entries, which makes the
+# table of contents hard to navigate in e-book readers
+epub_tocdepth = 2
+
 # translation tag
 # ---------------
 

Doc/library/dis.rst

@@ -1899,32 +1899,38 @@ iterations of the loop.
 
    The operand determines which intrinsic function is called:
 
-   +------------------------------------------+-----------------------------------+
-   | Operand                                  | Description                       |
-   +==========================================+===================================+
-   | ``INTRINSIC_2_INVALID``                  | Not valid                         |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_PREP_RERAISE_STAR``          | Calculates the                    |
-   |                                          | :exc:`ExceptionGroup` to raise    |
-   |                                          | from a ``try-except*``.           |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_TYPEVAR_WITH_BOUND``         | Creates a :class:`typing.TypeVar` |
-   |                                          | with a bound.                     |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_TYPEVAR_WITH_CONSTRAINTS``   | Creates a                         |
-   |                                          | :class:`typing.TypeVar` with      |
-   |                                          | constraints.                      |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_SET_FUNCTION_TYPE_PARAMS``   | Sets the ``__type_params__``      |
-   |                                          | attribute of a function.          |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_ADD_CONDITIONAL_ANNOTATION`` | Adds an annotation index to the   |
-   |                                          | ``__conditional_annotations__``   |
-   |                                          | set.                              |
-   +------------------------------------------+-----------------------------------+
+   +------------------------------------------+-----------------------------------------+
+   | Operand                                  | Description                             |
+   +==========================================+=========================================+
+   | ``INTRINSIC_2_INVALID``                  | Not valid                               |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_PREP_RERAISE_STAR``          | Calculates the                          |
+   |                                          | :exc:`ExceptionGroup` to raise          |
+   |                                          | from a ``try-except*``.                 |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_TYPEVAR_WITH_BOUND``         | Creates a :class:`typing.TypeVar`       |
+   |                                          | with a bound.                           |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_TYPEVAR_WITH_CONSTRAINTS``   | Creates a                               |
+   |                                          | :class:`typing.TypeVar` with            |
+   |                                          | constraints.                            |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_SET_FUNCTION_TYPE_PARAMS``   | Sets the ``__type_params__``            |
+   |                                          | attribute of a function.                |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_ADD_CONDITIONAL_ANNOTATION`` | Adds an annotation index to the         |
+   |                                          | ``__conditional_annotations__``         |
+   |                                          | set.                                    |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_MATCH_CLASS_ISINSTANCE``     | Do :func:`isinstance` checks for        |
+   |                                          | :ref:`Class patterns <class-patterns>`. |
+   +------------------------------------------+-----------------------------------------+
 
    .. versionadded:: 3.12
 
+   .. versionchanged:: 3.16
+      Added ``INTRINSIC_MATCH_CLASS_ISINSTANCE``.
+
 
 .. opcode:: LOAD_SPECIAL
 

Doc/library/optparse.rst

@@ -16,15 +16,12 @@ Choosing an argument parsing library
 The standard library includes three argument parsing libraries:
 
 * :mod:`getopt`: a module that closely mirrors the procedural C ``getopt`` API.
-  Included in the standard library since before the initial Python 1.0 release.
 * :mod:`!optparse`: a declarative replacement for ``getopt`` that
   provides equivalent functionality without requiring each application
-  to implement its own procedural option parsing logic. Included
-  in the standard library since the Python 2.3 release.
+  to implement its own procedural option parsing logic.
 * :mod:`argparse`: a more opinionated alternative to ``optparse`` that
   provides more functionality by default, at the expense of reduced application
-  flexibility in controlling exactly how arguments are processed. Included in
-  the standard library since the Python 2.7 and Python 3.2 releases.
+  flexibility in controlling exactly how arguments are processed.
 
 In the absence of more specific argument parsing design constraints, :mod:`argparse`
 is the recommended choice for implementing command line applications, as it offers

Include/internal/pycore_intrinsics.h

@@ -31,8 +31,9 @@
 #define INTRINSIC_SET_FUNCTION_TYPE_PARAMS       4
 #define INTRINSIC_SET_TYPEPARAM_DEFAULT          5
 #define INTRINSIC_ADD_CONDITIONAL_ANNOTATION     6
+#define INTRINSIC_MATCH_CLASS_ISINSTANCE         7
 
-#define MAX_INTRINSIC_2                          6
+#define MAX_INTRINSIC_2                          7
 
 typedef PyObject *(*intrinsic_func1)(PyThreadState* tstate, PyObject *value);
 typedef PyObject *(*intrinsic_func2)(PyThreadState* tstate, PyObject *value1, PyObject *value2);

Include/internal/pycore_magic_number.h

@@ -303,6 +303,7 @@ Known values:
     Python 3.16a1 3703 (Replace DELETE_GLOBAL with PUSH_NULL; STORE_GLOBAL)
     Python 3.16a1 3704 (Replace DELETE_ATTR with PUSH_NULL; STORE_ATTR)
     Python 3.16a1 3705 (Add INTRINSIC_ADD_CONDITIONAL_ANNOTATION)
+    Python 3.16a1 3706 (Add INTRINSIC_MATCH_CLASS_ISINSTANCE)
 
     Python 3.17 will start with 3750
 
@@ -312,7 +313,7 @@ Known values:
 
 */
 
-#define PYC_MAGIC_NUMBER 3705
+#define PYC_MAGIC_NUMBER 3706
 /* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
    (little-endian) and then appending b'\r\n'. */
 #define PYC_MAGIC_NUMBER_TOKEN \

Lib/_ast_unparse.py

@@ -925,7 +925,11 @@ def visit_Attribute(self, node):
         # Special case: 3.__abs__() is a syntax error, so if node.value
         # is an integer literal then we need to either parenthesize
         # it or add an extra space to get 3 .__abs__().
-        if isinstance(node.value, Constant) and isinstance(node.value.value, int):
+        # bool is a subclass of int, but True.real and False.real are
+        # valid without a space.
+        if (isinstance(node.value, Constant)
+                and isinstance(node.value.value, int)
+                and not isinstance(node.value.value, bool)):
             self.write(" ")
         self.write(".")
         self.write(node.attr)

Lib/idlelib/editor.py

@@ -1120,19 +1120,50 @@ def _close(self):
 
     def last_mtime(self):
         file = self.io.filename
-        return os.path.getmtime(file) if file else 0
+        if not file:
+            return None
+        try:
+            return os.path.getmtime(file)
+        except OSError:
+            # File is gone or cannot be stat'ed.
+            return None
 
     def focus_in_event(self, event):
         mtime = self.last_mtime()
-        if self.mtime != mtime:
+        if mtime == self.mtime:
+            return
+        if self.mtime is not None and mtime is None:
+            # The file was there and is now gone; reloading cannot work.
+            self.deleted_file_event(event)
+        else:
             self.mtime = mtime
-            if self. askyesno(
+            if self.askyesno(
               'Reload', '"%s"\n\nThis script has been modified by another program.'
               '\nDo you want to reload it?' % self.io.filename, parent=self.text):
                 self.io.loadfile(self.io.filename)
             else:
                 self.set_saved(False)
 
+    def deleted_file_event(self, event):
+        # The file was deleted or renamed while open; ask what to do with the
+        # buffer instead of offering a reload that could only fail.  Forget the
+        # old mtime before showing the dialog so a FocusIn delivered while this
+        # dialog (or a Close/Save As sub-dialog) is open does not reopen it; a
+        # successful Save As restores it via set_saved(True).
+        self.mtime = None
+        dialog = simpledialog.SimpleDialog(
+            self.text,
+            title='File Deleted',
+            text='"%s"\n\nThis file no longer exists.' % self.io.filename,
+            buttons=('Close', 'Save As', 'Ignore'),
+            default=1,
+            cancel=2)
+        choice = dialog.go()
+        if choice == 0:
+            self.close()
+        elif choice == 1:
+            self.io.save_as(event)
+
     def load_extensions(self):
         self.extensions = {}
         self.load_standard_extensions()

Lib/idlelib/idle_test/test_editor.py

@@ -1,7 +1,11 @@
 "Test editor, coverage 53%."
 
 from idlelib import editor
+import os
+import tempfile
+import types
 import unittest
+from pathlib import Path
 from collections import namedtuple
 from unittest import mock
 from test.support import requires
@@ -321,5 +325,81 @@ def test_rmenu_check_copy(self):
         eq(self.window.rmenu_check_cut(), 'normal')
 
 
+class LastMtimeTest(unittest.TestCase):
+    # Exercise last_mtime as an unbound method on a stub; no GUI needed.
+
+    def test_existing_file_returns_mtime(self):
+        with tempfile.TemporaryDirectory() as d:
+            p = os.path.join(d, 'f.py')
+            Path(p).touch()
+            stub = types.SimpleNamespace(io=types.SimpleNamespace(filename=p))
+            self.assertEqual(Editor.last_mtime(stub), os.path.getmtime(p))
+
+    def test_deleted_file_returns_none(self):
+        with tempfile.TemporaryDirectory() as d:
+            p = os.path.join(d, 'gone.py')
+            Path(p).touch()
+            os.remove(p)
+            stub = types.SimpleNamespace(io=types.SimpleNamespace(filename=p))
+            self.assertIsNone(Editor.last_mtime(stub))
+
+    def test_not_yet_created_filename(self):
+        # __init__ calls last_mtime() before self.mtime is set, so last_mtime()
+        # must not read self.mtime (the stub has no mtime attribute).
+        stub = types.SimpleNamespace(
+            io=types.SimpleNamespace(filename='/no/such/file.py'))
+        self.assertIsNone(Editor.last_mtime(stub))
+
+    def test_no_filename_returns_none(self):
+        stub = types.SimpleNamespace(io=types.SimpleNamespace(filename=None))
+        self.assertIsNone(Editor.last_mtime(stub))
+
+
+class DeletedFileEventTest(unittest.TestCase):
+    # Exercise the deleted-file handling as unbound methods; dialog is mocked.
+
+    def make_stub(self):
+        return types.SimpleNamespace(
+            mtime=1.0,
+            text=None,
+            io=types.SimpleNamespace(filename='/gone.py', save_as=mock.Mock()),
+            close=mock.Mock(),
+            set_saved=mock.Mock(),
+            deleted_file_event=mock.Mock(),
+            askyesno=mock.Mock(),
+            last_mtime=lambda: None)
+
+    def test_focus_in_routes_deleted_to_dialog(self):
+        stub = self.make_stub()
+        Editor.focus_in_event(stub, 'event')
+        stub.deleted_file_event.assert_called_once_with('event')
+        stub.askyesno.assert_not_called()
+
+    def _run_choice(self, choice):
+        stub = self.make_stub()
+        with mock.patch.object(editor.simpledialog, 'SimpleDialog') as SD:
+            SD.return_value.go.return_value = choice
+            Editor.deleted_file_event(stub, 'event')
+        return stub
+
+    def test_close_choice_closes_window(self):
+        stub = self._run_choice(0)
+        self.assertTrue(stub.close.called)
+        # mtime is cleared before Close so the queued FocusIn does not reprompt.
+        self.assertIsNone(stub.mtime)
+
+    def test_save_as_choice_clears_mtime_and_saves(self):
+        stub = self._run_choice(1)
+        stub.io.save_as.assert_called_once_with('event')
+        # A cancelled Save As leaves mtime None so it does not reprompt.
+        self.assertIsNone(stub.mtime)
+
+    def test_ignore_choice_clears_mtime(self):
+        stub = self._run_choice(2)
+        self.assertIsNone(stub.mtime)
+        stub.io.save_as.assert_not_called()
+        stub.set_saved.assert_not_called()
+
+
 if __name__ == '__main__':
     unittest.main(verbosity=2)

Lib/idlelib/idle_test/test_run.py

@@ -49,14 +49,15 @@ def __eq__(self, other):
             ('int.reel', AttributeError,
                  "type object 'int' has no attribute 'reel'. "
                  "Did you mean '.real' instead of '.reel'?\n"),  # More in 3.15.
+            (r'raise NameError("123\n456")', NameError, "123\n456\n"),
             )
 
     @force_not_colorized
     def test_get_message(self):
         for code, exc, msg in self.data:
             with self.subTest(code=code):
                 try:
-                    eval(compile(code, '', 'eval'))
+                    exec(compile(code, '', 'exec'))
                 except exc:
                     typ, val, tb = sys.exc_info()
                     actual = run.get_message_lines(typ, val, tb)[0]
@@ -68,15 +69,20 @@ def test_get_message(self):
                        new_callable=lambda: (lambda t, e: None))
     def test_get_multiple_message(self, mock):
         d = self.data
-        data2 = ((d[0], d[1]), (d[1], d[2]), (d[2], d[0]))
+        data2 = ((d[0], d[1]),
+                 (d[1], d[2]),
+                 (d[2], d[3]),
+                 (d[3], d[0]),
+                 (d[1], d[3]),
+                 (d[0], d[2]))
         subtests = 0
         for (code1, exc1, msg1), (code2, exc2, msg2) in data2:
             with self.subTest(codes=(code1,code2)):
                 try:
-                    eval(compile(code1, '', 'eval'))
+                    exec(compile(code1, '', 'exec'))
                 except exc1:
                     try:
-                        eval(compile(code2, '', 'eval'))
+                        exec(compile(code2, '', 'exec'))
                     except exc2:
                         with captured_stderr() as output:
                             run.print_exception()

Lib/idlelib/run.py

@@ -4,7 +4,6 @@
 f'''{sys.executable} -c "__import__('idlelib.run').run.main()"'''
 '.run' is needed because __import__ returns idlelib, not idlelib.run.
 """
-import contextlib
 import functools
 import io
 import linecache
@@ -244,15 +243,8 @@ def show_socket_error(err, address):
 
 
 def get_message_lines(typ, exc, tb):
-    "Return line composing the exception message."
-    if typ in (AttributeError, NameError):
-        # 3.10+ hints are not directly accessible from python (#44026).
-        err = io.StringIO()
-        with contextlib.redirect_stderr(err):
-            sys.__excepthook__(typ, exc, tb)
-        return [err.getvalue().split("\n")[-2] + "\n"]
-    else:
-        return traceback.format_exception_only(typ, exc)
+    "Return lines of the exception message, with any suggestion."
+    return list(traceback.TracebackException(typ, exc, tb).format_exception_only())
 
 
 def print_exception():