3.16.rst

What's new in Python 3.16

Editor:	TBD

This article explains the new features in Python 3.16, compared to 3.15.

For full details, see the :ref:`changelog <changelog>`.

Note

Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.16 moves towards release, so it's worth checking back even after reading earlier versions.

Summary --- release highlights

New features

Other language changes

• :meth:`memoryview.cast` now allows casting a multidimensional F-contiguous view to a one-dimensional view. (Contributed by Jaemin Park in :gh:`91484`.)
• :meth:`memoryview.cast` now accepts an order parameter. With order='F' it returns a zero-copy Fortran-contiguous (column-major) view of a flat buffer, which is useful for interfacing with column-major libraries. (Contributed by Serhiy Storchaka in :gh:`78959`.)
• :ref:`Frame objects <frame-objects>` now support :mod:`weak references <weakref>`. This allows associating extra data with active frames, for example in debuggers, without keeping the frames (and everything they reference) alive indefinitely. (Contributed by Łukasz Langa in :gh:`102960`.)

New modules

• None yet.

Improved modules

asyncio

• Add the mode parameter to :meth:`asyncio.loop.create_unix_server` and :func:`asyncio.start_unix_server` to set the permissions of the Unix socket file created for path. (Contributed by Sam Bull in :gh:`94984`.)

codecs

• On platforms that provide the C library's :manpage:`iconv(3)` function, every encoding known to iconv for which Python has no built-in codec is now available (for example cp1133). Prefixing an encoding name with iconv: forces the iconv-based codec even when a built-in codec of the same name exists. (Contributed by Serhiy Storchaka in :gh:`152997`.)

csv

• :meth:`csv.Sniffer.sniff` now deduces the dialect by trial parsing instead of heuristics based on matching isolated fragments and on character frequencies, so the result is consistent with how :func:`csv.reader` will parse the sample. It can now detect the escapechar parameter, accepts non-ASCII delimiters in the delimiters argument, no longer misdetects the delimiter when the sample contains delimiter characters inside quoted fields, and no longer takes quadratic time on quoted samples. The results may differ from those of earlier Python versions. (Contributed by Serhiy Storchaka in :gh:`83273`.)

curses

• The :mod:`curses` character-cell window methods now accept a full character cell --- a spacing character optionally followed by combining characters --- in addition to a single integer or byte character. This affects :meth:`~curses.window.addch`, :meth:`~curses.window.bkgd`, :meth:`~curses.window.bkgdset`, :meth:`~curses.window.border`, :meth:`~curses.window.box`, :meth:`~curses.window.echochar`, :meth:`~curses.window.hline`, :meth:`~curses.window.insch` and :meth:`~curses.window.vline`. Also add the wide-character read methods :meth:`~curses.window.get_wstr` and :meth:`~curses.window.in_wstr`, the counterparts of :meth:`~curses.window.getstr` and :meth:`~curses.window.instr` that return a :class:`str` rather than :class:`bytes`, and the module functions :func:`curses.erasewchar`, :func:`curses.killwchar` and :func:`curses.wunctrl`, the wide-character counterparts of :func:`curses.erasechar`, :func:`curses.killchar` and :func:`curses.unctrl`. On a narrow (non-ncursesw) build the character cell holds a single character without combining marks, representable as one byte in the window's encoding, and :meth:`~curses.window.in_wstr` returns its decoded text. (Contributed by Serhiy Storchaka in :gh:`151757`.)
• Add the :class:`curses.complexchar` type, representing a styled character cell (its text, attributes and color pair), and the window methods :meth:`~curses.window.in_wch` and :meth:`~curses.window.getbkgrnd` that return one --- the counterparts of :meth:`~curses.window.inch` and :meth:`~curses.window.getbkgd`. The character-cell methods, such as :meth:`~curses.window.addch` and :meth:`~curses.window.border`, now also accept a :class:`~curses.complexchar`. These work whether or not Python was built against a wide-character-aware curses library; on a narrow build a cell holds a single character representable as one byte in the window's encoding (so only 8-bit locales are supported). (Contributed by Serhiy Storchaka in :gh:`152233`.)
• Add the :class:`curses.complexstr` type, an immutable run of styled cells (the string counterpart of :class:`~curses.complexchar`), and the window method :meth:`~curses.window.in_wchstr` that returns one. The string-cell methods :meth:`~curses.window.addstr`, :meth:`~curses.window.addnstr`, :meth:`~curses.window.insstr` and :meth:`~curses.window.insnstr` now also accept a :class:`~curses.complexstr`. Like :class:`~curses.complexchar`, it works whether or not Python was built against a wide-character-aware curses library. (Contributed by Serhiy Storchaka in :gh:`152233`.)
• The wide-character :mod:`curses` functions and methods :meth:`~curses.window.get_wch`, :meth:`~curses.window.get_wstr`, :func:`curses.unget_wch`, :func:`curses.erasewchar`, :func:`curses.killwchar` and :func:`curses.wunctrl` now also work when Python is not built against a wide-character-aware curses library, on an 8-bit locale, where each character is a single byte in the relevant encoding. :func:`curses.ungetch` now also accepts a one-character string, like :func:`curses.unget_wch`; on a wide-character build it can be any character (previously a multibyte character raised :exc:`OverflowError`). (Contributed by Serhiy Storchaka in :gh:`152470`.)
• Add support for multiple terminals to the :mod:`curses` module: the new functions :func:`curses.newterm`, :func:`curses.set_term` and :func:`curses.new_prescr`, the corresponding :ref:`screen <curses-screen-objects>` object, and the :meth:`window.use() <curses.window.use>` method. (Contributed by Serhiy Storchaka in :gh:`90092`.)
• Add the :mod:`curses` window methods :meth:`~curses.window.attr_get`, :meth:`~curses.window.attr_set`, :meth:`~curses.window.attr_on`, :meth:`~curses.window.attr_off` and :meth:`~curses.window.color_set`, which pass the color pair as a separate argument instead of packing it into the attribute value, and the corresponding WA_* attribute constants. (Contributed by Serhiy Storchaka in :gh:`152219`.)
• Add the :func:`curses.term_attrs` function, which returns the supported video attributes as :ref:`WA_* <curses-wa-constants>` values, the counterpart of :func:`curses.termattrs`. (Contributed by Serhiy Storchaka in :gh:`152332`.)
• Add the :mod:`curses` functions :func:`curses.alloc_pair`, :func:`curses.find_pair`, :func:`curses.free_pair` and :func:`curses.reset_color_pairs` for dynamic color-pair management, available when built against a wide-character ncurses with extended-color support. (Contributed by Serhiy Storchaka in :gh:`151774`.)
• Add the :mod:`curses` functions :func:`~curses.scr_dump`, :func:`~curses.scr_restore`, :func:`~curses.scr_init` and :func:`~curses.scr_set`, which dump the whole screen to a file and restore it. (Contributed by Serhiy Storchaka in :gh:`152260`.)
• Add the :mod:`curses` window method :meth:`~curses.window.dupwin`, which returns a new window that is an independent duplicate of an existing one. (Contributed by Serhiy Storchaka in :gh:`152258`.)
• Add the soft-label-key functions to the :mod:`curses` module, which manage a row of labels along the bottom line of the screen: :func:`~curses.slk_init`, :func:`~curses.slk_set`, :func:`~curses.slk_label`, :func:`~curses.slk_refresh`, :func:`~curses.slk_noutrefresh`, :func:`~curses.slk_clear`, :func:`~curses.slk_restore`, :func:`~curses.slk_touch`, the attribute functions :func:`~curses.slk_attron`, :func:`~curses.slk_attroff`, :func:`~curses.slk_attrset`, :func:`~curses.slk_attr`, :func:`~curses.slk_attr_on`, :func:`~curses.slk_attr_off`, :func:`~curses.slk_attr_set`, and :func:`~curses.slk_color`. (Contributed by Serhiy Storchaka in :gh:`152263`.)
• Add the :mod:`curses` key-management functions :func:`~curses.define_key`, :func:`~curses.key_defined` and :func:`~curses.keyok`, available when built against an ncurses with NCURSES_EXT_FUNCS. (Contributed by Serhiy Storchaka in :gh:`152334`.)
• Add the :func:`curses.has_mouse` function and the :meth:`curses.window.mouse_trafo` method, completing the :mod:`curses` mouse interface. (Contributed by Serhiy Storchaka in :gh:`152325`.)
• Add :mod:`curses` functions and window methods that report state which could previously only be set, such as :meth:`curses.window.is_keypad`, :meth:`curses.window.getparent` and :func:`curses.is_cbreak`, available when built against an ncurses with NCURSES_EXT_FUNCS. (Contributed by Serhiy Storchaka in :gh:`151776`.)
• Add :func:`curses.nofilter`, which undoes the effect of :func:`curses.filter`. (Contributed by Serhiy Storchaka in :gh:`151744`.)
• :class:`curses.textpad.Textbox` now supports entering and reading back the full Unicode range, including combining characters, when curses is built with wide-character support. (Contributed by Serhiy Storchaka in :gh:`133031`.)

ctypes

• Add :func:`ctypes.util.struct` for generating :class:`~ctypes.Structure` types from an annotation-based syntax, similar to how the :mod:`dataclasses` module is used. (Contributed by Peter Bierma in :gh:`104533`.)
• Add :func:`ctypes.util.wrap_dll_function` for generating function pointers through a function signature. (Contributed by Peter Bierma in :gh:`153903`.)

encodings

• Add the utf-7-imap codec, implementing the modified UTF-7 encoding used for international IMAP4 mailbox names (RFC 3501). (Contributed by Serhiy Storchaka in :gh:`66788`.)

gzip

• :func:`gzip.open` now accepts an optional argument mtime which is passed on to the constructor of the :class:`~gzip.GzipFile` class. (Contributed by Marin Misur in :gh:`91372`.)

io

• Add :meth:`io.BytesIO.peek` method to read without advancing position. (Contributed by Marcel Martin in :gh:`90533`.)

imaplib

• Add the :meth:`~imaplib.IMAP4.id` method, a wrapper for the ID command (RFC 2971). (Contributed by Serhiy Storchaka in :gh:`98092`.)
• Add the :meth:`~imaplib.IMAP4.move` method, a wrapper for the MOVE command (RFC 6851). (Contributed by Serhiy Storchaka in :gh:`77508`.)
• Add the :meth:`~imaplib.IMAP4.login_plain` method, which authenticates using the PLAIN SASL mechanism (RFC 4616) and supports non-ASCII user names and passwords. (Contributed by Przemysław Buczkowski and Serhiy Storchaka in :gh:`89869`.)
• Non-ASCII mailbox names are now automatically encoded as modified UTF-7 (RFC 3501, section 5.1.3) in the default mode, so international mailbox names can be passed as ordinary :class:`str` without enabling UTF8=ACCEPT (under which they are sent as UTF-8). (Contributed by Serhiy Storchaka in :gh:`49555`.)
• The :meth:`~imaplib.IMAP4.copy`, :meth:`~imaplib.IMAP4.move`, :meth:`~imaplib.IMAP4.fetch`, :meth:`~imaplib.IMAP4.store`, :meth:`~imaplib.IMAP4.search`, :meth:`~imaplib.IMAP4.sort`, :meth:`~imaplib.IMAP4.thread` and :meth:`~imaplib.IMAP4.expunge` methods now accept a keyword-only uid argument that selects the corresponding UID command, as a more convenient alternative to :meth:`~imaplib.IMAP4.uid`. (Contributed by Serhiy Storchaka in :gh:`153502`.)
• :meth:`~imaplib.IMAP4.search`, :meth:`~imaplib.IMAP4.sort` and :meth:`~imaplib.IMAP4.thread` (and the corresponding uid commands) now encode :class:`str` search criteria to the declared charset, so international search text can be passed as an ordinary :class:`str`. When charset is None (as it must be under UTF8=ACCEPT), the criteria are sent using the connection encoding instead. (Contributed by Serhiy Storchaka in :gh:`153494`.)
• Command methods now accept structured arguments, so the module takes care of quoting instead of the caller. A message_set and lists of flags or other atoms can be passed as sequences instead of preformatted strings, and the :meth:`~imaplib.IMAP4.search`, :meth:`~imaplib.IMAP4.fetch`, :meth:`~imaplib.IMAP4.sort`, :meth:`~imaplib.IMAP4.thread` and :meth:`~imaplib.IMAP4.uid` methods accept a params keyword argument that substitutes and quotes ? placeholders, in the manner of :mod:`sqlite3` parameter substitution. (Contributed by Serhiy Storchaka in :gh:`153521`.)

ipaddress

Add :meth:`~ipaddress.IPv4Network.next_network` and :meth:`~ipaddress.IPv6Network.next_network` methods to find the next nearest network with a specific prefix size.

logging

• :class:`~logging.handlers.TimedRotatingFileHandler` now uses the creation time instead of the last modification time of an existing log file as the basis for the first rotation after handler creation, if supported by the OS and file system. This allows it to be used in short-running programs that start and end before the rotation interval expires. (Contributed by Iván Márton and Serhiy Storchaka in :gh:`84649`.)

lzma

• Add support of new BCJ filters ARM64 and RISC-V via :const:`!lzma.FILTER_ARM64` and :const:`!lzma.FILTER_RISCV`. Note that the new filters will work only if the runtime library supports them. ARM64 filter requires lzma 5.4.0 or newer while RISC-V requires 5.6.0 or newer. (Contributed by Chien Wong in :gh:`115988`.)

math

• Added trigonometric functions that work in units of half turns, rather than radians. The new functions :func:`math.acospi`, :func:`math.asinpi`, :func:`math.atanpi`, and :func:`math.atan2pi` return half-turn angles. The new functions :func:`math.cospi`, :func:`math.sinpi`, and :func:`math.tanpi` take half-turn angle arguments. These functions are recommended by IEEE 754-2019 and standardized in C23. (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

• Add :func:`os.pidfd_getfd` for duplicating a file descriptor from another process via a pidfd. Available on Linux 5.6+. (Contributed by Maurycy Pawłowski-Wieroński in :gh:`149464`.)

pydoc

• Modernize the HTML output of :mod:`pydoc`. The pages generated by the :mod:`pydoc` HTTP server now use semantic HTML5 markup and a new style sheet based on the python-docs-theme used by docs.python.org, with dark mode support. Class members inherited from other classes are collapsed by default. (Contributed by Serhiy Storchaka in :gh:`153906`.)

re

• :mod:`re` now supports set operations and nested sets in character classes, as described in Unicode Technical Standard #18: set difference ([A--B]), intersection ([A&&B]) and union ([A||B]), where an operand may be a nested set written in square brackets. For example, [a-z--[aeiou]] matches an ASCII lowercase consonant. (Contributed by Serhiy Storchaka in :gh:`152100`.)
• Regular expressions now support Unicode property escapes \p{...} and \P{...}, which match a character by a Unicode property -- for example \p{Lu} (an uppercase letter), \p{Cased} or \p{ASCII}. See :ref:`the regular expression syntax <re-syntax>` for the supported properties. (Contributed by Serhiy Storchaka in :gh:`95555`.)

shlex

• Add keyword-only parameter force to :func:`shlex.quote` to force quoting a string, even if it is already safe for a shell without being quoted. (Contributed by Jay Berry in :gh:`148846`.)

symtable

• :func:`symtable.symtable` now accepts an AST object, like the builtin :func:`compile`. (Contributed by Serhiy Storchaka in :gh:`153844`.)

tkinter

• Added many :class:`tkinter.ttk.Treeview` methods wrapping the enhanced ttk::treeview widget commands from Tk 9.1, such as :meth:`~tkinter.ttk.Treeview.sort`, :meth:`~tkinter.ttk.Treeview.search`, :meth:`~tkinter.ttk.Treeview.expand`, :meth:`~tkinter.ttk.Treeview.collapse`, :meth:`~tkinter.ttk.Treeview.hide`, :meth:`~tkinter.ttk.Treeview.unhide`, and methods for cell focus, selection and tagging. The :meth:`~tkinter.ttk.Treeview.expand` and :meth:`~tkinter.ttk.Treeview.collapse` methods (without recursion) also work on Tk older than 9.1. (Contributed by Serhiy Storchaka in :gh:`151910`.)
• Added new :class:`!tkinter.Text` methods :meth:`~tkinter.Text.edit_canundo` and :meth:`~tkinter.Text.edit_canredo` which return whether an undo or redo is possible. (Contributed by Serhiy Storchaka in :gh:`151674`.)
• Added new :class:`!tkinter.Text` methods :meth:`~tkinter.Text.sync` and :meth:`~tkinter.Text.pendingsync` which control and report the synchronization of the displayed view with the underlying text. (Contributed by Serhiy Storchaka in :gh:`151675`.)
• Added the :meth:`ttk.Style.theme_styles <tkinter.ttk.Style.theme_styles>` method which returns the list of styles defined in a theme. (Contributed by Serhiy Storchaka in :gh:`151920`.)
• Added new :class:`!tkinter.Canvas` methods :meth:`~tkinter.Canvas.rchars` which replaces the text or coordinates of canvas items, and :meth:`~tkinter.Canvas.rotate` which rotates the coordinates of canvas items. (Contributed by Serhiy Storchaka in :gh:`151876`.)
• Added a :meth:`!validate` method to the :class:`!tkinter.Entry` and :class:`!tkinter.Spinbox` widgets, which forces an evaluation of the validation command. (Contributed by Serhiy Storchaka in :gh:`151878`.)
• Added the :meth:`tkinter.Menu.postcascade` method, and the :meth:`~tkinter.Misc.tk_scaling` and :meth:`~tkinter.Misc.tk_inactive` methods which respectively query or set the display scaling factor and report the user idle time. (Contributed by Serhiy Storchaka in :gh:`151881`.)
• Added the :meth:`!tk_print` method to :class:`tkinter.Canvas` and :class:`tkinter.Text` which prints the contents of the widget using the native print dialog. It requires Tk 8.7/9.0 or newer. (Contributed by Serhiy Storchaka in :gh:`153256`.)
• Added new window-management methods :meth:`~tkinter.Misc.winfo_isdark` (dark mode detection), :meth:`~tkinter.Wm.wm_iconbadge` (application icon badge) and :meth:`~tkinter.Wm.wm_stackorder` (toplevel stacking order). (Contributed by Serhiy Storchaka in :gh:`151874`.)
• Added the :meth:`~tkinter.Misc.tk_appname`, :meth:`~tkinter.Misc.tk_useinputmethods` and :meth:`~tkinter.Misc.tk_caret` methods, exposing the application send name, the X Input Methods state and the input method caret location. (Contributed by Serhiy Storchaka in :gh:`151886`.)
• Added support for more options in :class:`!tkinter.PhotoImage` methods: the format parameter of :meth:`~tkinter.PhotoImage.put`, the metadata parameter of :meth:`~tkinter.PhotoImage.put`, :meth:`~tkinter.PhotoImage.read`, :meth:`~tkinter.PhotoImage.write` and :meth:`~tkinter.PhotoImage.data`, and the withalpha parameter of :meth:`~tkinter.PhotoImage.get`. (Contributed by Serhiy Storchaka in :gh:`151890`.)
• Added the :meth:`~tkinter.PhotoImage.redither` method which recalculates the dithered image when its data was supplied in pieces. (Contributed by Serhiy Storchaka in :gh:`151888`.)
• :class:`tkinter.OptionMenu` now accepts arbitrary :class:`!tkinter.Menubutton` options as keyword arguments, which can also override its default appearance. (Contributed by Serhiy Storchaka in :gh:`101284`.)
• The :mod:`tkinter.simpledialog` dialogs were modernized to match the look and feel of the native Tk dialogs. :class:`!tkinter.simpledialog.SimpleDialog` and the :func:`~tkinter.simpledialog.askinteger`, :func:`~tkinter.simpledialog.askfloat` and :func:`~tkinter.simpledialog.askstring` dialogs are now built from the themed :mod:`tkinter.ttk` widgets instead of the classic :mod:`tkinter` widgets; the :class:`!tkinter.simpledialog.Dialog` base class still defaults to the classic widgets for compatibility. Both :class:`!Dialog` and :class:`!SimpleDialog` gained a use_ttk parameter that selects between the classic Tk widgets and the themed ttk widgets. :class:`!SimpleDialog` also gained bitmap and detail parameters, draws the standard icons with themed images in the ttk version, and accepts mappings of button options as buttons entries. (Contributed by Serhiy Storchaka in :gh:`59396`.)
• The :class:`!tkinter.filedialog.FileDialog` dialog and its :class:`!tkinter.filedialog.LoadFileDialog` and :class:`!tkinter.filedialog.SaveFileDialog` subclasses are now built from the themed :mod:`tkinter.ttk` widgets by default instead of the classic :mod:`tkinter` widgets, and gained a use_ttk parameter to select between them. (Contributed by Serhiy Storchaka in :gh:`59396`.)
• Added the :mod:`tkinter.systray` module which provides the :class:`~tkinter.systray.SysTrayIcon` class as an interface to the system tray icon and the :func:`~tkinter.systray.notify` function which sends a desktop notification. They require Tk 8.7/9.0 or newer. (Contributed by Serhiy Storchaka in :gh:`153259`.)
• :class:`tkinter.scrolledtext.ScrolledText` gained a use_ttk parameter to use the themed :mod:`tkinter.ttk` frame and scroll bar instead of the classic :mod:`tkinter` widgets. (Contributed by Serhiy Storchaka in :gh:`59396`.)
• :class:`tkinter.font.Font` can now wrap a font description without creating a new named font, by passing it as font with exists=True and no name. This avoids a loss of precision in :meth:`~tkinter.font.Font.actual`, :meth:`~tkinter.font.Font.measure` and :meth:`~tkinter.font.Font.metrics`. (Contributed by Serhiy Storchaka in :gh:`143990`.)
• Added the :mod:`tkinter.fontchooser` module which provides the :class:`~tkinter.fontchooser.FontChooser` class as an interface to the native font selection dialog. (Contributed by Serhiy Storchaka in :gh:`72880`.)
• Values of several Tcl object types returned by :mod:`tkinter` are now converted to the corresponding Python type instead of being wrapped in a :class:`!_tkinter.Tcl_Obj`: index, window, nsName and parsedVarName objects to :class:`str`, and pixel screen distances with no unit suffix to :class:`int` or :class:`float`. (Contributed by Serhiy Storchaka in :gh:`153513`.)

xml

• Add support for multiple multi-byte encodings in the :mod:`XML parser <xml.parsers.expat>`: "cp932", "cp949", "cp950", "Big5", "EUC-JP", "GB2312", "GBK", "johab", and "Shift_JIS". Add partial support (only BMP characters) for multi-byte encodings "Big5-HKSCS", "EUC_JIS-2004", "EUC_JISX0213", "Shift_JIS-2004", "Shift_JISX0213", "utf-8-sig" and non-standard aliases like "UTF8" (without hyphen). The parser now raises :exc:`ValueError` for known unsupported multi-byte encodings such as "ISO-2022-JP" or "raw-unicode-escape" instead of failing later, when encountering non-ASCII data. (Contributed by Serhiy Storchaka in :gh:`62259`.)

zipfile

• Add :meth:`ZipFile.remove() <zipfile.ZipFile.remove>` to remove a member from an archive's central directory, and :meth:`ZipFile.repack() <zipfile.ZipFile.repack>` to reclaim the space used by the local file entries of removed members. (Contributed by Danny Lin in :gh:`51067`.)

Optimizations

re

• Character class escapes (\d, \D, \s, \S, \w and \W) outside a character set, and character sets containing a single such escape (such as [\d] or [^\s]), are now compiled to a single CATEGORY opcode instead of being wrapped in an IN block. This speeds up matching of patterns such as \d+ and reduces the size of the compiled byte code. (Contributed by Serhiy Storchaka in :gh:`152033` and Pieter Eendebak in :gh:`152056`.)

module_name

• TODO

Removed

annotationlib

• The :meth:`!annotationlib.ForwardRef._evaluate` method which has been deprecated since Python 3.14. Use :meth:`annotationlib.ForwardRef.evaluate` or :func:`typing.evaluate_forward_ref` instead.

array

• The 'u' format code (:c:type:`wchar_t`) which has been deprecated in documentation since Python 3.3 and at runtime since Python 3.13. Use 'w' format code instead (:c:type:`Py_UCS4`, always 4 bytes).

asyncio

• The :func:`!asyncio.iscoroutinefunction` which has been deprecated since Python 3.14. Use :func:`inspect.iscoroutinefunction` instead.
• The event loop policy system, including the :class:`!asyncio.AbstractEventLoopPolicy`, :class:`!asyncio.DefaultEventLoopPolicy`, :class:`!asyncio.WindowsSelectorEventLoopPolicy` and :class:`!asyncio.WindowsProactorEventLoopPolicy` classes and the :func:`!asyncio.get_event_loop_policy` and :func:`!asyncio.set_event_loop_policy` functions, which have been deprecated since Python 3.14. Use :func:`asyncio.run` or :class:`asyncio.Runner` with a custom loop_factory instead.

functools

• Calling the Python implementation of :func:`functools.reduce` with function or sequence as keyword arguments has been deprecated since Python 3.14.

logging

• Support for custom logging handlers with the strm argument is deprecated and scheduled for removal in Python 3.16. Define handlers with the stream argument instead.

mimetypes

• Valid extensions start with a '.' or are empty for :meth:`mimetypes.MimeTypes.add_type`. Undotted extensions now raise a :exc:`ValueError`.

shutil

• The :exc:`!ExecError` exception which has been deprecated since Python 3.14. It has not been used by any function in :mod:`!shutil` since Python 3.4. (Contributed by Stan Ulbrych in :gh:`149567`.)

symtable

• The :meth:`!symtable.Class.get_methods` method which has been deprecated since Python 3.14.

sys

• The :func:`!_enablelegacywindowsfsencoding` function which has been deprecated since Python 3.13. Use the :envvar:`PYTHONLEGACYWINDOWSFSENCODING` environment variable instead. (Contributed by Stan Ulbrych in :gh:`149595`.)

sysconfig

• The :func:`!sysconfig.expand_makefile_vars` function which has been deprecated since Python 3.14. Use the vars argument of :func:`sysconfig.get_paths` instead. (Contributed by Stan Ulbrych in :gh:`149499`.)

tarfile

• The undocumented and unused :attr:`!tarfile.TarFile.tarfile` attribute has been deprecated since Python 3.13.

Deprecated

New deprecations

• :mod:`abc`
  • Soft-deprecated since Python 3.3 :class:`abc.abstractclassmethod`, :class:`abc.abstractstaticmethod`, and :class:`abc.abstractproperty` now raise a :exc:`DeprecationWarning`. These classes will be removed in Python 3.21, instead use :func:`abc.abstractmethod` with :func:`classmethod`, :func:`staticmethod`, and :class:`property` respectively.
• :mod:`ast`:
  • Classes slice, Index, ExtSlice, Suite, Param, AugLoad and AugStore, deprecated since Python 3.9, are no longer imported by from ast import * and issue a deprecation warning on use. The classes are slated for removal in Python 3.21. These types are not generated by the parser or accepted by the code generator.
  • The dims property of ast.Tuple objects, deprecated since Python 3.9, now issues a deprecation warning on use. This property is slated for removal in 3.21. Use ast.Tuple.elts instead.
• :mod:`struct`:
  • Soft-deprecated since Python 3.15, using 'F' and 'D' type codes are now deprecated. These codes will be removed in Python 3.21. Use instead two-letter forms 'Zf' and 'Zd'. (Contributed by Sergey B Kirpichev in :gh:`121249`.)
• :mod:`tempfile`
  • The private tempfile._TemporaryFileWrapper name is deprecated and is slated for removal in Python 3.21. Use the new public :class:`tempfile.TemporaryFileWrapper` instead, which is the return type of :func:`tempfile.NamedTemporaryFile`.
• :mod:`tkinter`:
  • :func:`tkinter.filedialog.askopenfiles` is deprecated and slated for removal in Python 3.19. Opening several files at once is error-prone, and the returned list cannot be used in a :keyword:`with` statement. Iterate over the names returned by :func:`~tkinter.filedialog.askopenfilenames` and open them one by one instead. (Contributed by Serhiy Storchaka in :gh:`152638`.)

Porting to Python 3.16

This section lists previously described changes and other bugfixes that may require changes to your code.

• In :mod:`tkinter`, the name parameter of the :meth:`~tkinter.Misc.wait_variable`, :meth:`~tkinter.Misc.setvar` and :meth:`~tkinter.Misc.getvar` methods and the value parameter of :meth:`!setvar` are now required. Calling these methods without them, which formerly defaulted to 'PY_VAR' and '1', now raises :exc:`TypeError`. (Contributed by Serhiy Storchaka in :gh:`152587`.)

Build changes

• Remove the bundled copy of the libmpdec decimal library from the CPython source tree to simplify maintenance and updates. The :mod:`decimal` module will now unconditionally use the system's libmpdec decimal library. Also remove the now unused :option:`!--with-system-libmpdec` :program:`configure` flag. This change has no impact on binary releases of Python, which have been built against a separate copy of libmpdec for the past several releases.

  (Contributed by Sergey B Kirpichev in :gh:`115119`.)

• Add a :option:`--with-build-details-suffix` configure flag to allow Linux distributions that co-install multiple versions of Python in the same tree to avoid build-details.json clashes.

  (Contributed by Stefano Rivera in :gh:`131372`.)

• Add the :option:`--with-curses` :program:`configure` option to select the curses backend for the :mod:`curses` and :mod:`curses.panel` modules. In addition to ncursesw and ncurses, it can now build against the system's native curses library (for example on NetBSD or Solaris), with wide-character support when the library provides it. :option:`--without-curses` excludes the modules from the build.

  (Contributed by Serhiy Storchaka in :gh:`136687`.)

C API changes

New features

• TODO

Porting to Python 3.16

• :c:func:`PyType_ClearCache` is now a no-op as the type cache is now implemented per-type. It still returns the current version tag.

Deprecated C APIs

• :c:func:`PyGen_New`, :c:func:`PyGen_NewWithQualName`, :c:func:`PyCoro_New`, and :c:func:`PyAsyncGen_New` are deprecated. They are scheduled for removal in 3.18.

Removed C APIs