Sync pre-release CPython main branch from GitHub (2026-07-30)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`f4b1d3e`](https://www.github.com/python/cpython/commit/f4b1d3e891d0d2055e53df3ccb84030bcaa148b5) (committed 2026-07-30 02:31:40+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`8b048eb`](https://www.github.com/python/cpython/commit/8b048eb35eb7f83dbff86dd11c7fdb37caab9e7a) (commit date: 2026-07-28 17:35:26+00:00)
- Imported: (`3.16.0a0`) - [`f4b1d3e`](https://www.github.com/python/cpython/commit/f4b1d3e891d0d2055e53df3ccb84030bcaa148b5) (commit date: 2026-07-30 02:31:40+00:00)

# Noteworthy file changes

- Low-signal files (6 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GMOePScSBH_L3wMJAMbIL2Kl1ZY9br0LAAAz

Differential Revision: D114171568

fbshipit-source-id: b11ad9cba0e9578dc8af307f6cd66220ae98ca45

Author: generatedunixname1734921407115435

Doc/library/asyncio-task.rst

@@ -433,6 +433,10 @@ unless it is :exc:`asyncio.CancelledError`,
 is also included in the exception group.
 The same special case is made for
 :exc:`KeyboardInterrupt` and :exc:`SystemExit` as in the previous paragraph.
+There is an additional special case made only for the body of the
+``async with``: if it raises :exc:`GeneratorExit` and none of the
+other tasks raise exceptions that would be reported, then the
+:exc:`GeneratorExit` is reraised.
 
 Task groups are careful not to mix up the internal cancellation used to
 "wake up" their :meth:`~object.__aexit__` with cancellation requests
@@ -456,6 +460,10 @@ reported by :meth:`asyncio.Task.cancelling`.
    Improved handling of simultaneous internal and external cancellations
    and correct preservation of cancellation counts.
 
+.. versionchanged:: 3.15
+
+   Addition of the special case for :exc:`GeneratorExit`.
+
 Sleeping
 ========
 

Doc/library/multiprocessing.rst

@@ -2536,7 +2536,7 @@ with the :class:`Pool` class.
       Callbacks should complete immediately since otherwise the thread which
       handles the results will get blocked.
 
-   .. method:: imap(func, iterable[, chunksize])
+   .. method:: imap(func, iterable, chunksize=1, *, buffersize=None)
 
       A lazier version of :meth:`.map`.
 
@@ -2550,12 +2550,27 @@ with the :class:`Pool` class.
       ``next(timeout)`` will raise :exc:`multiprocessing.TimeoutError` if the
       result cannot be returned within *timeout* seconds.
 
-   .. method:: imap_unordered(func, iterable[, chunksize])
+      The *iterable* is collected immediately rather than lazily, unless a
+      *buffersize* is specified to limit the number of submitted tasks whose
+      results have not yet been yielded. If the buffer is full, iteration over
+      the *iterables* pauses until a result is yielded from the buffer.
+      To fully utilize pool's capacity when using this feature,
+      set *buffersize* at least to the number of processes in pool
+      (to consume *iterable* as you go), or even higher
+      (to prefetch the next ``N=buffersize-processes`` arguments).
+
+      .. versionchanged:: next
+         Added the *buffersize* parameter.
+
+   .. method:: imap_unordered(func, iterable, chunksize=1, *, buffersize=None)
 
       The same as :meth:`imap` except that the ordering of the results from the
       returned iterator should be considered arbitrary.  (Only when there is
       only one worker process is the order guaranteed to be "correct".)
 
+      .. versionchanged:: next
+         Added the *buffersize* parameter.
+
    .. method:: starmap(func, iterable[, chunksize])
 
       Like :meth:`~multiprocessing.pool.Pool.map` except that the

Doc/library/os.rst

@@ -802,9 +802,9 @@ process and user.
    Returns information identifying the current operating system.
    The return value is a :class:`uname_result`.
 
-   On macOS, iOS and Android, this returns the *kernel* name and version (i.e.,
+   On macOS, iOS and Android, this returns the *kernel* name and release (i.e.,
    ``'Darwin'`` on macOS and iOS; ``'Linux'`` on Android). :func:`platform.uname`
-   can be used to get the user-facing operating system name and version on iOS and
+   can be used to get the user-facing operating system name and release on iOS and
    Android.
 
    .. seealso::

Doc/library/platform.rst

@@ -141,6 +141,8 @@ Cross platform
    Returns the system's release, e.g. ``'2.2.0'`` or ``'NT'``. An empty string is
    returned if the value cannot be determined.
 
+   On iOS and Android, this is the user-facing OS release. To obtain the
+   Darwin or Linux kernel release, use :func:`os.uname`.
 
 .. function:: system()
 
@@ -163,9 +165,6 @@ Cross platform
    Returns the system's release version, e.g. ``'#3 on degas'``. An empty string is
    returned if the value cannot be determined.
 
-   On iOS and Android, this is the user-facing OS version. To obtain the
-   Darwin or Linux kernel version, use :func:`os.uname`.
-
 .. function:: uname()
 
    Fairly portable uname interface. Returns a :func:`~collections.namedtuple`

Doc/whatsnew/3.16.rst

@@ -376,6 +376,22 @@ math
   (Contributed by Jeff Epler in :gh:`150534`.)
 
 
+multiprocessing
+---------------
+
+* Add the optional ``buffersize`` parameter to
+  :meth:`multiprocessing.pool.Pool.imap` and
+  :meth:`multiprocessing.pool.Pool.imap_unordered` to limit the number of
+  submitted tasks whose results have not yet been yielded. If the buffer is
+  full, iteration over the *iterables* pauses until a result is yielded from
+  the buffer. To fully utilize pool's capacity when using this feature, set
+  *buffersize* at least to the number of processes in pool (to consume
+  *iterable* as you go), or even higher (to prefetch the next
+  ``N=buffersize-processes`` arguments).
+
+  (Contributed by Oleksandr Baltian in :gh:`136871`.)
+
+
 os
 --
 
@@ -606,7 +622,7 @@ module_name
 
 
 Removed
-=======
+========
 
 annotationlib
 -------------

Include/internal/pycore_opcode_metadata.h

@@ -174,10 +174,23 @@ async def _aexit(self, et, exc):
                 self._parent_task.uncancel()
                 self._parent_task.cancel()
             try:
-                raise BaseExceptionGroup(
-                    'unhandled errors in a TaskGroup',
-                    self._errors,
-                ) from None
+                # If the *only* error is a GeneratorExit from the body
+                # of the group, then instead of raising an
+                # ExceptionGroup we raise GeneratorExit. This ensures
+                # that async generators that use TaskGroup properly
+                # swallow the exception on `aclose()` while ensuring
+                # that no exceptions from subtasks are swallowed.
+                if (
+                    et is not None
+                    and issubclass(et, GeneratorExit)
+                    and len(self._errors) == 1
+                ):
+                    raise exc
+                else:
+                    raise BaseExceptionGroup(
+                        'unhandled errors in a TaskGroup',
+                        self._errors,
+                    ) from None
             finally:
                 exc = None
 

Include/internal/pycore_uop_metadata.h

@@ -412,53 +412,12 @@ def find_library(name):
                    _get_soname(_findLib_gcc(name)) or _get_soname(_findLib_ld(name))
 
 
-# Listing loaded libraries on other systems will try to use
-# functions common to Linux and a few other Unix-like systems.
-# See the following for several platforms' documentation of the same API:
-# https://man7.org/linux/man-pages/man3/dl_iterate_phdr.3.html
-# https://man.freebsd.org/cgi/man.cgi?query=dl_iterate_phdr
-# https://man.openbsd.org/dl_iterate_phdr
-# https://docs.oracle.com/cd/E88353_01/html/E37843/dl-iterate-phdr-3c.html
-if (os.name == "posix" and
-    sys.platform not in {"darwin", "ios", "tvos", "watchos"}):
-    import ctypes
-    if hasattr((_libc := ctypes.CDLL(None)), "dl_iterate_phdr"):
-
-        class _dl_phdr_info(ctypes.Structure):
-            _fields_ = [
-                ("dlpi_addr", ctypes.c_void_p),
-                ("dlpi_name", ctypes.c_char_p),
-                ("dlpi_phdr", ctypes.c_void_p),
-                ("dlpi_phnum", ctypes.c_ushort),
-            ]
-
-        _dl_phdr_callback = ctypes.CFUNCTYPE(
-            ctypes.c_int,
-            ctypes.POINTER(_dl_phdr_info),
-            ctypes.c_size_t,
-            ctypes.POINTER(ctypes.py_object),
-        )
-
-        @_dl_phdr_callback
-        def _info_callback(info, _size, data):
-            libraries = data.contents.value
-            name = os.fsdecode(info.contents.dlpi_name)
-            libraries.append(name)
-            return 0
-
-        _dl_iterate_phdr = _libc["dl_iterate_phdr"]
-        _dl_iterate_phdr.argtypes = [
-            _dl_phdr_callback,
-            ctypes.POINTER(ctypes.py_object),
-        ]
-        _dl_iterate_phdr.restype = ctypes.c_int
-
-        def dllist():
-            """Return a list of loaded shared libraries in the current process."""
-            libraries = []
-            _dl_iterate_phdr(_info_callback,
-                             ctypes.byref(ctypes.py_object(libraries)))
-            return libraries
+# On platforms which provide dl_iterate_phdr(), dllist() is implemented
+# in _ctypes.
+try:
+    from _ctypes import dllist
+except ImportError:
+    pass
 
 
 @dataclass(slots=True, frozen=True)