Sync pre-release CPython main branch from GitHub (2026-07-28)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`c8eb79d`](https://www.github.com/python/cpython/commit/c8eb79d5e89196449992fe50978d6b8845dc6681) (committed 2026-07-28 05:00:39+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`993a0c6`](https://www.github.com/python/cpython/commit/993a0c65a7b1836aa2087dff197b2fffa62d5b4f) (commit date: 2026-07-26 22:37:20+00:00)
- Imported: (`3.16.0a0`) - [`c8eb79d`](https://www.github.com/python/cpython/commit/c8eb79d5e89196449992fe50978d6b8845dc6681) (commit date: 2026-07-28 05:00:39+00:00)

# Noteworthy file changes

- Test files (3 added)
- Low-signal files (6 added, 1 removed) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GLzr7hzVqf6sfRwGAAYX2f5-i05Dbr0LAAAz

Reviewed By: itamaro

Differential Revision: D113872493

fbshipit-source-id: d3ea73f29eb1b2b90a42f02e7eded63b113bdab9

Author: generatedunixname1734921407115435

Doc/c-api/sys.rst

@@ -433,7 +433,7 @@ accessible to C code.  They all work with the current interpreter thread's
    This function is safe to call before :c:func:`Py_Initialize`. When called
    after runtime initialization, existing audit hooks are notified and may
    silently abort the operation by raising an error subclassed from
-   :class:`Exception` (other errors will not be silenced).
+   :class:`RuntimeError` (other errors will not be silenced).
 
    The hook function is always called with an :term:`attached thread state` by
    the Python interpreter that raised the event.
@@ -447,7 +447,7 @@ accessible to C code.  They all work with the current interpreter thread's
 
       If the interpreter is initialized, this function raises an auditing event
       ``sys.addaudithook`` with no arguments. If any existing hooks raise an
-      exception derived from :class:`Exception`, the new hook will not be
+      exception derived from :class:`RuntimeError`, the new hook will not be
       added and the exception is cleared. As a result, callers cannot assume
       that their hook has been added unless they control all existing hooks.
 
@@ -462,6 +462,11 @@ accessible to C code.  They all work with the current interpreter thread's
 
    .. versionadded:: 3.8
 
+   .. versionchanged:: 3.8.1
+
+      Exceptions derived from :class:`Exception` but not :class:`RuntimeError`
+      are no longer suppressed.
+
 
 .. _processcontrol:
 

Doc/library/curses.rst

@@ -129,6 +129,8 @@ Initialization and termination
    and return the previously current screen.
    Returns ``None`` if the previous screen was the one created by
    :func:`initscr`.
+   Raises :exc:`error` if *screen* has no terminal,
+   as is the case for a screen returned by :func:`new_prescr`.
 
    .. versionadded:: next
 

Doc/library/test.rst

@@ -961,6 +961,59 @@ The :mod:`!test.support` module defines the following functions:
    :mod:`tracemalloc` is enabled.
 
 
+.. currentmodule:: test.support.isolation
+
+.. decorator:: runInSubprocess()
+
+   Decorator that runs the decorated test in a fresh interpreter subprocess, in
+   isolation, so that it does not share global or interpreter state with the
+   rest of the test run.  It can decorate a test method or a whole
+   :class:`~unittest.TestCase` subclass.  Decorated methods must take no extra
+   arguments.  A failure, error or skip in the subprocess is reported for the
+   corresponding test, and individual :meth:`subtests
+   <unittest.TestCase.subTest>` that fail or are skipped are reported
+   individually.  A reported failure or error shows the original subprocess
+   traceback as the cause of the exception.
+
+   When a **method** is decorated, only that method runs in a subprocess; all
+   fixtures (:meth:`~unittest.TestCase.setUp` / :meth:`~unittest.TestCase.tearDown`,
+   :meth:`~unittest.TestCase.setUpClass` / :meth:`~unittest.TestCase.tearDownClass`
+   and ``setUpModule()`` / ``tearDownModule()``) run both in the parent process
+   (as usual) and in the subprocess around the method.
+
+   When a **class** is decorated, the whole class runs in a single subprocess,
+   and :meth:`~unittest.TestCase.setUpClass`,
+   :meth:`~unittest.TestCase.tearDownClass`, :meth:`~unittest.TestCase.setUp`
+   and :meth:`~unittest.TestCase.tearDown` run once each in the subprocess and
+   are skipped in the parent process.  A failure or skip of
+   :meth:`~unittest.TestCase.setUpClass` in the subprocess is reported for the
+   whole class.  ``setUpModule()`` cannot be controlled by a class decorator,
+   so it still runs in the parent process too; test it with
+   :data:`runningInSubprocess` if needed.
+
+   The subprocess inherits the enabled resources (``-u``), memory limit
+   (``-M``) and verbosity (``-v``) of the parent test run, so that
+   :func:`~test.support.requires_resource`, :func:`~test.support.requires`,
+   :func:`~test.support.bigmemtest` and the like behave consistently in both
+   processes.
+
+   The test is skipped on platforms without subprocess support.
+
+
+.. data:: runningInSubprocess
+
+   ``True`` while the code runs in the isolated subprocess spawned by
+   :func:`runInSubprocess`, and ``False`` otherwise (including in the parent
+   process and in a normal, non-isolated test run).  Fixtures such as
+   :meth:`~unittest.TestCase.setUp`, :meth:`~unittest.TestCase.tearDown`,
+   :meth:`~unittest.TestCase.setUpClass`, :meth:`~unittest.TestCase.tearDownClass`,
+   ``setUpModule()`` and ``tearDownModule()`` can test it to choose which code
+   to run in the subprocess.
+
+
+.. currentmodule:: test.support
+
+
 .. function:: check_free_after_iterating(test, iter, cls, args=())
 
    Assert instances of *cls* are deallocated after iterating.

Doc/whatsnew/3.15.rst

@@ -873,6 +873,14 @@ Other language changes
   imports ``pkg.sub.mod``.
   (Contributed by Gregory P. Smith in :gh:`83065`.)
 
+* File names of Stable ABI extensions that use the ``.so`` suffix may now
+  include a multiarch tuple, for example, ``foo.abi3-x86-64-linux-gnu.so``.
+  This permits stable ABI extensions for multiple architectures to be
+  co-installed into the same directory, without clashing with each
+  other, as regular dynamic extensions do.
+  (Contributed by Stefano Rivera in :gh:`122931`.)
+
+
 
 Default interactive shell
 =========================

Include/internal/pycore_interp_structs.h

@@ -977,7 +977,6 @@ struct _is {
     struct _obmalloc_state *obmalloc;
 
     PyObject *audit_hooks;
-    PyMutex audit_hooks_mutex;
     PyType_WatchCallback type_watchers[TYPE_MAX_WATCHERS];
     PyCode_WatchCallback code_watchers[CODE_MAX_WATCHERS];
     PyContext_WatchCallback context_watchers[CONTEXT_MAX_WATCHERS];

Lib/collections/__init__.py

@@ -553,6 +553,9 @@ class Counter(dict):
     or multiset.  Elements are stored as dictionary keys and their counts
     are stored as dictionary values.
 
+    When constructed from a Mapping or Counter, the original object's
+    values will be used as the initial counts.
+
     >>> c = Counter('abcdeabcdabcaba')  # count elements from a string
 
     >>> c.most_common(3)                # three most common elements

Lib/csv.py

@@ -563,22 +563,40 @@ def _detect_doublequote(self, lines, delimiter, quotechar, escapechar):
     def _detect_skipinitialspace(self, lines, delimiter, quotechar,
                                  escapechar, doublequote):
         """
-        True only if every field following a delimiter starts with
-        a space.
+        Detect whether the spaces following a delimiter are a part of
+        the format or of the data.
         """
-        skipinitialspace = False
-        try:
-            for row in self._make_reader(lines, delimiter, quotechar,
-                                         escapechar,
-                                         doublequote=doublequote,
-                                         skipinitialspace=False):
-                for field in row[1:]:
-                    if not field.startswith(' '):
-                        return False
-                    skipinitialspace = True
-        except Error:
-            pass
-        return skipinitialspace
+        results = []
+        for skipinitialspace in False, True:
+            rows = []
+            try:
+                rows.extend(self._make_reader(
+                    lines, delimiter, quotechar, escapechar,
+                    doublequote=doublequote,
+                    skipinitialspace=skipinitialspace))
+            except Error:
+                # Keep the rows parsed before the error.
+                pass
+            results.append([row for row in rows if row])
+        if results[0] == results[1]:
+            return False  # No evidence.
+        counts = [[len(row) for row in rows] for rows in results]
+        if counts[0] != counts[1]:
+            # Prefer the more consistent row widths.
+            return len(set(counts[1])) <= len(set(counts[0]))
+        # Only some spaces are stripped.  A field differs only if
+        # a space was skipped at its start, which tells the padding
+        # apart from the spaces inside quoted or escaped fields.
+        if not all(kept_field != skipped_field
+                   for kept_row, skipped_row in zip(*results)
+                   for kept_field, skipped_field in zip(kept_row[1:],
+                                                        skipped_row[1:])):
+            return False
+        # The first field of a row is commonly not padded ('a, b, c'),
+        # so the first fields need only agree with each other.
+        first = [kept_row[0] != skipped_row[0]
+                 for kept_row, skipped_row in zip(*results)]
+        return all(first) or not any(first)
 
     def has_header(self, sample):
         # Creates a dictionary of types of data in each column. If any

Lib/importlib/abc.py

@@ -1,6 +1,7 @@
 """Abstract base classes related to import."""
 from . import _bootstrap_external
 from . import machinery
+
 try:
     import _frozen_importlib
 except ImportError as exc:
@@ -11,10 +12,12 @@
     import _frozen_importlib_external
 except ImportError:
     _frozen_importlib_external = _bootstrap_external
-from ._abc import Loader
 import abc
 
 
+# Public API
+from ._abc import Loader
+
 __all__ = [
     'Loader', 'MetaPathFinder', 'PathEntryFinder',
     'ResourceLoader', 'InspectLoader', 'ExecutionLoader',

Lib/importlib/machinery.py

@@ -1,5 +1,9 @@
 """The machinery of importlib: finders, loaders, hooks, etc."""
 
+lazy import warnings
+
+
+# Public API
 from ._bootstrap import ModuleSpec
 from ._bootstrap import BuiltinImporter
 from ._bootstrap import FrozenImporter
@@ -33,8 +37,6 @@ def all_suffixes():
 
 
 def __getattr__(name):
-    import warnings
-
     if name == 'DEBUG_BYTECODE_SUFFIXES':
         warnings.warn('importlib.machinery.DEBUG_BYTECODE_SUFFIXES is '
                       'deprecated; use importlib.machinery.BYTECODE_SUFFIXES '

Lib/importlib/util.py

@@ -1,19 +1,23 @@
 """Utility code for constructing importers, etc."""
+
+from ._bootstrap import _resolve_name
+from ._bootstrap import _find_spec
+
+import _imp
+import sys
+import types
+
+
+# Public API
 from ._abc import Loader
 from ._bootstrap import module_from_spec
-from ._bootstrap import _resolve_name
 from ._bootstrap import spec_from_loader
-from ._bootstrap import _find_spec
 from ._bootstrap_external import MAGIC_NUMBER
 from ._bootstrap_external import cache_from_source
 from ._bootstrap_external import decode_source
 from ._bootstrap_external import source_from_cache
 from ._bootstrap_external import spec_from_file_location
 
-import _imp
-import sys
-import types
-
 
 def source_hash(source_bytes):
     "Return the hash of *source_bytes* as used in hash-based pyc files."