3.14.0a5.rst

Update macOS installer to use ncurses 6.5.

The iOS test runner now strips the log prefix from each line output by the test suite.

Fix several bugs in extraction by switching to an AST parser in :program:`pygettext`.

Add test.support.reset_code, which can be used to reset various bytecode-level optimizations and local instrumentation for a function.

Disable test_embed test cases that segfault on BOLT instrument binaries. The tests are only disabled when BOLT is enabled.

Add an option --parallel-threads=N to the regression test runner that runs individual tests in multiple threads in parallel in order to find concurrency bugs. Note that most of the test suite is not yet reviewed for thread-safety or annotated with @thread_unsafe when necessary.

When using :func:`urllib.parse.urlsplit` and :func:`urllib.parse.urlparse` host parsing would not reject domain names containing square brackets ([ and ]). Square brackets are only valid for IPv6 and IPvFuture hosts according to RFC 3986 Section 3.2.2.

Fix a possible NULL pointer dereference in :c:func:`!PySys_AddWarnOptionUnicode`.

Fix bug in the folding of quoted strings when flattening an email message using a modern email policy. Previously when a quoted string was folded so that it spanned more than one line, the surrounding quotes and internal escapes would be omitted. This could theoretically be used to spoof header lines using a carefully constructed quoted string if the resulting rendered email was transmitted or re-parsed.

Fix a potential denial of service in the :mod:`imaplib` module. When connecting to a malicious server, it could cause an arbitrary amount of memory to be allocated. On many systems this is harmless as unused virtual memory is only a mapping, but if this hit a virtual address size limit it could lead to a :exc:`MemoryError` or other process crash. On unusual systems or builds where all allocated memory is touched and backed by actual ram or storage it could've consumed resources doing so until similarly crashing.

Comparison pages with highlighted changes generated by the :class:`difflib.HtmlDiff` class now support dark mode.

Raise :exc:`sqlite3.ProgrammingError` if a user-defined SQL function with invalid number of parameters is created. Patch by Erlend Aasland.

Update bundled pip to 25.0.1

Fix crash in :mod:`warnings`, when calling _release_lock() with no existing lock.

_pyio.FileIO.readall() now allocates, resizes, and fills a data buffer using the same algorithm _io.FileIO.readall() uses.

Update the locale alias mapping in the :mod:`locale` module to match the latest X Org locale alias mapping and support new locales in Glibc 2.41.

Put CLI calendar highlighting in private class, removing highlight_day from public :class:`calendar.TextCalendar` API. Patch by Hugo van Kemenade.

Fix bugs where :class:`sqlite3.Row` objects could segfault if their inherited :attr:`~sqlite3.Cursor.description` was set to None. Patch by Erlend Aasland.

Add :meth:`bytearray.resize` method so :class:`bytearray` can be efficiently resized in place.

Unlikely errors in preparing arguments for :mod:`ctypes` callback are now handled in the same way as errors raised in the callback of in converting the result of the callback -- using :func:`sys.unraisablehook` instead of :func:`sys.excepthook` and not setting :data:`sys.last_exc` and other variables.

Corrected :exc:`ValueError` message for :class:`asyncio.Barrier` and :class:`threading.Barrier`.

Fix an integer overflow in the :mod:`csv` module when writing a data field larger than 2GB.

Add a socket timeout keyword argument to :class:`logging.handlers.SysLogHandler`.

Always lazy import warnings in :mod:`threading`. Patch by Taneli Hukkinen.

Improve import time of :mod:`subprocess` by lazy importing locale and signal. Patch by Taneli Hukkinen.

In :mod:`sqlite3`, handle out-of-memory when creating user-defined SQL functions.

Optimize _pyio.FileIO.readinto by avoiding unnecessary objects and copies using :func:`os.readinto`.

Support reporting call graph information from :func:`!asyncio.staggered.staggered_race`.

Add :func:`os.readinto` to read into a :ref:`buffer object <bufferobjects>` from a file descriptor.

Fix :mod:`pydoc` for methods with the __module__ attribute equal to None.

Fix FORCE_COLOR and NO_COLOR when empty strings. Patch by Hugo van Kemenade.

Scheduled the deprecation of the check_home argument of :func:`sysconfig.is_python_build` to Python 3.15.

Deprecate :func:`!sysconfig.expand_makefile_vars`, in favor of using :func:`sysconfig.get_paths` with the vars argument.

Removed an incorrect optimization relating to eager tasks in :class:`asyncio.TaskGroup` that resulted in cancellations being missed.

Release the enter frame reference within :mod:`bdb` callback

Reduce import time of :mod:`pstats` and :mod:`zipfile` by up to 20%, by removing unnecessary imports to :mod:`typing`. Patch by Bénédikt Tran.

Fix a :exc:`NameError` in :func:`!sysconfig.expand_makefile_vars`. Patch by Bénédikt Tran.

Fix a crash when setting state on an exhausted :class:`array.array` iterator.

Fix traceback.TracebackException._format_syntax_error not to fail on exceptions with custom metadata.

Do not attempt to set SO_REUSEPORT on sockets of address families other than AF_INET and AF_INET6, as it is meaningless with these address families, and the call with fail with Linux kernel 6.12.9 and newer.

Improve import time of :mod:`tomllib` by removing typing, string, and tomllib._types imports. Patch by Taneli Hukkinen.

:mod:`tracemalloc`: Fix race conditions when :func:`tracemalloc.stop` is called by a thread, while other threads are tracing memory allocations. Patch by Victor Stinner.

Add specialized opcodes to opcode.opname.

Reduce import time of :mod:`gettext` by up to ten times, by importing :mod:`re` on demand. In particular, re is no longer implicitly exposed as gettext.re. Patch by Eli Schwartz.

Reduce the import time of :mod:`optparse` when no help text is printed. Patch by Eli Schwartz.

Fix possible extra reference when using objects returned by :func:`hashlib.sha256` under :term:`free threading`.

Reduce the import time of :mod:`csv` by up to five times, by importing :mod:`re` on demand. In particular, re is no more implicitly exposed as csv.re. Patch by Bénédikt Tran.

Support the name keyword argument for eager tasks in :func:`asyncio.loop.create_task`, :func:`asyncio.create_task` and :func:`asyncio.TaskGroup.create_task`, by passing on all kwargs to the task factory set by :func:`asyncio.loop.set_task_factory`.

Improve the performance of :func:`base64.b16decode` by up to ten times by more efficiently checking the byte-string for hexadecimal digits. Reduce the import time of :mod:`base64` by up to six times, by no longer importing :mod:`re`. Patch by Bénédikt Tran, Chris Markiewicz, and Adam Turner.

When using macOS system libffi, support for complex types in :mod:`ctypes` is now checked at runtime (macOS 10.15 or newer). The types must also be available at build time.

Fix PyREPL failure when :data:`os.environ` is overwritten with an invalid value.

Default to stdout isatty for color detection instead of stderr. Patch by Hugo van Kemenade.

Add locking to :mod:`warnings` to avoid some data races when free-threading is used. Change _warnings_runtime_state.mutex to be a recursive mutex and expose it to :mod:`warnings`, via the :func:`!_acquire_lock` and :func:`!_release_lock` functions. The lock is held when filters and _filters_version are updated.

Add :func:`sys._is_immortal` for identifying :term:`immortal` objects at runtime.

Fix :func:`!asyncio.staggered.staggered_race` leaking tasks and issuing an unhandled exception.

:const:`uuid.NIL` and :const:`uuid.MAX` are now available to represent the Nil and Max UUID formats as defined by RFC 9562.

:meth:`zipfile.ZipFile.writestr` now respect SOURCE_DATE_EPOCH that distributions can set centrally and have build tools consume this in order to produce reproducible output.

Fix incorrect handling of negative read sizes in :meth:`HTTPResponse.read <http.client.HTTPResponse.read>`. Patch by Yury Manushkin.

Fixed a frame reference leak in :mod:`bdb`.

Completely support random access of uncompressed unencrypted read-only zip files obtained by :meth:`ZipFile.open <zipfile.ZipFile.open>`.

Avoid reusing quote types in :func:`ast.unparse` if not needed.

Fix exceptions and incomplete writes after :class:`!asyncio._SelectorTransport` is closed before writes are completed.

Add missing Deprecation warnings for :const:`importlib.machinery.DEBUG_BYTECODE_SUFFIXES`, :const:`importlib.machinery.OPTIMIZED_BYTECODE_SUFFIXES`, :class:`importlib.machinery.WindowsRegistryFinder`, :class:`importlib.abc.ResourceLoader`, :meth:`importlib.abc.SourceLoader.path_mtime`.

When -E is set, only ignore PYTHON_COLORS and not FORCE_COLOR/NO_COLOR/TERM when colourising output. Patch by Hugo van Kemenade.

Add :attr:`pathlib.Path.info` attribute, which stores an object implementing the :class:`pathlib.types.PathInfo` protocol (also new). The object supports querying the file type and internally caching :func:`~os.stat` results. Path objects generated by :meth:`~pathlib.Path.iterdir` are initialized with file type information gleaned from scanning the parent directory.

Fix handling of the secure argument of :class:`logging.handlers.SMTPHandler`.

Do not recreate unnamed section on every read in :class:`configparser.ConfigParser`. Patch by Andrey Efremov.

Deprecate pdb.Pdb.curframe_locals

Fix _pyrepl crash when entering a double CTRL-Z on an overflowing line.

Fix round-trip invariance for backslash continuations in :func:`tokenize.untokenize`.

Add :func:`asyncio.capture_call_graph` and :func:`asyncio.print_call_graph` functions.

Quitting :mod:`pdb` in inline mode will emit a confirmation prompt and exit gracefully now, instead of printing an exception traceback.

Fixed issue in NamespaceReader where a non-path item in a namespace path, such as a sentinel added by an editable installer, would break resource loading.

Add the :func:`ctypes.util.dllist` function to list the loaded shared libraries for the current process.

Add IMAP4 IDLE support to the :mod:`imaplib` module. Patch by Forest.

Show tab completions menu below the current line, which results in less janky behaviour, and fixes a cursor movement bug. Patch by Daniel Hollas

Support custom messages for domain errors in the :mod:`math` module (:func:`math.sqrt`, :func:`math.log` and :func:`math.atanh` were modified as examples). Patch by Charlie Zhao and Sergey B Kirpichev.

Use :func:`os.copy_file_range` in :func:`shutil.copy`, :func:`shutil.copy2`, and :func:`shutil.copyfile` functions by default. An underlying Linux system call gives filesystems an opportunity to implement the use of copy-on-write (in case of btrfs and XFS) or server-side copy (in the case of NFS.) Patch by Illia Volochii.

Add attribute and item access support to :class:`string.Formatter` in auto-numbering mode, which allows format strings like '{.name}' and '{[1]}'.

Simplify displaying the IDLE doc by only copying the text section of idle.html to idlelib/help.html. Patch by Stan Ulbrych.

Require Sphinx 8.1.3 or later to build the Python documentation. Patch by Adam Turner.

Document that :const:`string.printable` is not printable in the POSIX sense. In particular, :meth:`string.printable.isprintable() <str.isprintable>` returns :const:`False`. Patch by Bénédikt Tran.

Replace the opcode BINARY_SUBSCR and its family by BINARY_OP with oparg NB_SUBSCR.

Fixed a race in _Py_qsbr_reserve in the free threading build.

Remove the internal LLTRACE macro (use :c:macro:`Py_DEBUG` instead).

Improve JIT performance for generators.

Fix thread safety of :c:func:`PyList_Insert` in free-threading builds.

Fix race condition when raising :exc:`MemoryError` in the free threaded build.

Fix thread safety of :c:func:`PyList_SetItem` in free-threading builds. Patch by Kumar Aditya.

Fix an issue where the "lltrace" debug feature could have been incorrectly enabled for some frames.

On FreeBSD, :data:`sys.platform` doesn't contain the major version anymore. It is always 'freebsd', instead of 'freebsd13' or 'freebsd14'.

Fix null pointer dereference in :func:`syslog.openlog` when an audit hook raises an exception.

Improve memory layout of JIT traces. Patch by Diego Russo

Add fast path for medium-size integers in :c:func:`PyLong_FromUnsignedLong`, :c:func:`PyLong_FromUnsignedLongLong` and :c:func:`PyLong_FromSize_t`.

The free-threaded version of the cyclic garbage collector has been optimized to conditionally use CPU prefetch instructions during the collection. This can reduce collection times by making it more likely that data is in the CPU cache when it is needed. The prefetch instructions are enabled if the number of long-lived objects (objects surviving a full collection) exceeds a threshold.

Fix f-strings such as f'{expr=}' sometimes not displaying the full expression when the expression contains !=.

Treat debug expressions in f-string as raw strings. Patch by Pablo Galindo

Fix the potential races in get/set dunder methods __annotations__, __annotate__ and __type_params__ for function object, and add related tests.

Add frame of except* to traceback when it wraps a naked exception.

Collect JIT memory stats using pystats. Patch by Diego Russo.

Specialize BINARY_OP for bitwise logical operations on compact ints.

Undocumented and unused private C-API functions _PyTrash_begin and _PyTrash_end are removed.

Add a marking phase to the free-threaded GC. This is similar to what was done in GH-126491. Since the free-threaded GC does not have generations and is not incremental, the marking phase looks for all objects reachable from known roots. The roots are objects known to not be garbage, like the module dictionary for :mod:`sys`. For most programs, this marking phase should make the GC a bit faster since typically less work is done per object.

Add opcode BINARY_OP_EXTEND which executes a pair of functions (guard and specialization functions) accessed from the inline cache.

A new type of interpreter has been added to CPython. This interpreter uses tail calls for its instruction handlers. Preliminary benchmark results suggest 7-11% geometric mean faster on pyperformance (depending on platform), and up to 30% faster on Python-intensive workloads. This interpreter currently only works on newer compilers, such as clang-19. Other compilers will continue using the old interpreter. Patch by Ken Jin, with ideas on how to implement this in CPython by Mark Shannon, Garret Gu, Haoran Xu, and Josh Haberman.

Improve performance of iterating over lists and tuples by using a freelist for the iterator objects.

The time to handle a LINE event in sys.monitoring (and sys.settrace) is now independent of the number of lines in the code object.

Restore terminal control characters on REPL exit.

Improved the SyntaxWarning message for invalid escape sequences to clarify that such sequences will raise a SyntaxError in future Python releases. The new message also suggests a potential fix, i.e., Did you mean "\\e"?.

Fix handling of :attr:`UnicodeError.start` and :attr:`UnicodeError.end` values in the :func:`codecs.replace_errors` error handler. Patch by Bénédikt Tran.

Fix handling of :attr:`UnicodeError.start` and :attr:`UnicodeError.end` values in the :func:`codecs.backslashreplace_errors` error handler. Patch by Bénédikt Tran.

Fix handling of :attr:`UnicodeError.start` and :attr:`UnicodeError.end` values in the :func:`codecs.xmlcharrefreplace_errors` error handler. Patch by Bénédikt Tran.

Slightly optimize the :class:`int` deallocator.

Fixed the error when resizing terminal in Python REPL. Patch by Semyon Moroz.

Fix crash with gi_frame.f_locals when generator frames outlive their generator. Patch by Mikhail Efimov.

Add :func:`turtle.fill`, :func:`turtle.poly` and :func:`turtle.no_animation` context managers. Patch by Marie Roald and Yngve Mardal Moe.

If the current working directory cannot be determined due to permissions, then import will no longer raise :exc:`PermissionError`. Patch by Alex Willmer.

Added support for the Partitioned cookie flag in :mod:`http.cookies`.

Update :c:func:`PyGC_Enable()`, :c:func:`PyGC_Disable()`, :c:func:`PyGC_IsEnabled()` to use atomic operation for thread-safety at free-threading build. Patch by Donghee Na.

Implement :c:func:`PyUnicode_KIND` and :c:func:`PyUnicode_DATA` as function, in addition to the macros with the same names. The macros rely on C bit fields which have compiler-specific layout. Patch by Victor Stinner.

Remove :c:func:`PySequence_Fast` from the limited C API, since this function has to be used with :c:macro:`PySequence_Fast_GET_ITEM` which never worked in the limited C API. Patch by Victor Stinner.

Add :c:func:`PyUnstable_IsImmortal` for determining whether an object is :term:`immortal`.

Remove _PyInterpreterState_GetConfigCopy() and _PyInterpreterState_SetConfig() private functions. Use instead :c:func:`PyConfig_Get` and :c:func:`PyConfig_Set`, public C API added by PEP 741 "Python Configuration C API". Patch by Victor Stinner.

Remove the private _Py_InitializeMain() function. It was a :term:`provisional API` added to Python 3.8 by PEP 587. Patch by Victor Stinner.

Add :c:func:`PyUnstable_TryIncRef` and :c:func:`PyUnstable_EnableTryIncRef` unstable APIs. These are helpers for dealing with unowned references in a thread-safe way, particularly in the free threading build.

Add :c:func:`PyImport_ImportModuleAttr` and :c:func:`PyImport_ImportModuleAttrString` helper functions to import a module and get an attribute of the module. Patch by Victor Stinner.

The following private functions are deprecated and planned for removal in Python 3.18:

• :c:func:`!_PyBytes_Join`: use :c:func:`PyBytes_Join`.
• :c:func:`!_PyDict_GetItemStringWithError`: use :c:func:`PyDict_GetItemStringRef`.
• :c:func:`!_PyDict_Pop()`: use :c:func:`PyDict_Pop`.
• :c:func:`!_PyLong_Sign()`: use :c:func:`PyLong_GetSign`.
• :c:func:`!_PyLong_FromDigits` and :c:func:`!_PyLong_New`: use :c:func:`PyLongWriter_Create`.
• :c:func:`!_PyThreadState_UncheckedGet`: use :c:func:`PyThreadState_GetUnchecked`.
• :c:func:`!_PyUnicode_AsString`: use :c:func:`PyUnicode_AsUTF8`.
• :c:func:`!_Py_HashPointer`: use :c:func:`Py_HashPointer`.
• :c:func:`!_Py_fopen_obj`: use :c:func:`Py_fopen`.

The pythoncapi-compat project can be used to get these new public functions on Python 3.13 and older.

Patch by Victor Stinner.

Remove some internal test APIs for the experimental JIT compiler.

Convert the :mod:`decimal` module to use PEP 757 C API (export-import integers), offering some speed-up if the integer part of the :class:`~decimal.Decimal` instance is small. Patch by Sergey B Kirpichev.

Drop test_embed from PGO training, whose contribution in recent versions is considered to be ignorable.

Fix compile errors with Clang 9 and older due to lack of __attribute__((fallthrough)) support.