| **************************** |
| What's New In Python 3.8 |
| **************************** |
| |
| .. Rules for maintenance: |
| |
| * Anyone can add text to this document. Do not spend very much time |
| on the wording of your changes, because your text will probably |
| get rewritten to some degree. |
| |
| * The maintainer will go through Misc/NEWS periodically and add |
| changes; it's therefore more important to add your changes to |
| Misc/NEWS than to this file. |
| |
| * This is not a complete list of every single change; completeness |
| is the purpose of Misc/NEWS. Some changes I consider too small |
| or esoteric to include. If such a change is added to the text, |
| I'll just remove it. (This is another reason you shouldn't spend |
| too much time on writing your addition.) |
| |
| * If you want to draw your new text to the attention of the |
| maintainer, add 'XXX' to the beginning of the paragraph or |
| section. |
| |
| * It's OK to just add a fragmentary note about a change. For |
| example: "XXX Describe the transmogrify() function added to the |
| socket module." The maintainer will research the change and |
| write the necessary text. |
| |
| * You can comment out your additions if you like, but it's not |
| necessary (especially when a final release is some months away). |
| |
| * Credit the author of a patch or bugfix. Just the name is |
| sufficient; the e-mail address isn't necessary. |
| |
| * It's helpful to add the bug/patch number as a comment: |
| |
| XXX Describe the transmogrify() function added to the socket |
| module. |
| (Contributed by P.Y. Developer in :issue:`12345`.) |
| |
| This saves the maintainer the effort of going through the Mercurial log |
| when researching a change. |
| |
| This article explains the new features in Python 3.8, compared to 3.7. |
| |
| 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 3.8 moves towards release, |
| so it's worth checking back even after reading earlier versions. |
| |
| |
| Summary -- Release highlights |
| ============================= |
| |
| .. This section singles out the most important changes in Python 3.8. |
| Brevity is key. |
| |
| |
| .. PEP-sized items next. |
| |
| |
| |
| New Features |
| ============ |
| |
| Parallel filesystem cache for compiled bytecode files |
| ----------------------------------------------------- |
| |
| The new :envvar:`PYTHONPYCACHEPREFIX` setting (also available as |
| :option:`-X` ``pycache_prefix``) configures the implicit bytecode |
| cache to use a separate parallel filesystem tree, rather than |
| the default ``__pycache__`` subdirectories within each source |
| directory. |
| |
| The location of the cache is reported in :data:`sys.pycache_prefix` |
| (:const:`None` indicates the default location in ``__pycache__`` |
| subdirectories). |
| |
| (Contributed by Carl Meyer in :issue:`33499`.) |
| |
| |
| Other Language Changes |
| ====================== |
| |
| * A :keyword:`continue` statement was illegal in the :keyword:`finally` clause |
| due to a problem with the implementation. In Python 3.8 this restriction |
| was lifted. |
| (Contributed by Serhiy Storchaka in :issue:`32489`.) |
| |
| * The :class:`int` type now has a new :meth:`~int.as_integer_ratio` method |
| compatible with the existing :meth:`float.as_integer_ratio` method. |
| (Contributed by Lisa Roach in :issue:`33073`.) |
| |
| * Added support of ``\N{name}`` escapes in :mod:`regular expressions <re>`. |
| (Contributed by Jonathan Eunice and Serhiy Storchaka in :issue:`30688`.) |
| |
| * Dict and dictviews are now iterable in reversed insertion order using |
| :func:`reversed`. (Contributed by Rémi Lapeyre in :issue:`33462`.) |
| |
| * The syntax allowed for keyword names in function calls was further |
| restricted. In particular, ``f((keyword)=arg)`` is no longer allowed. It was |
| never intended to permit more than a bare name on the left-hand side of a |
| keyword argument assignment term. See :issue:`34641`. |
| |
| * Iterable unpacking is now allowed without parentheses in :keyword:`yield` |
| and :keyword:`return` statements. |
| (Contributed by David Cuthbert and Jordan Chapman in :issue:`32117`.) |
| |
| * A backslash-character pair that is not a valid escape sequence generates |
| a :exc:`DeprecationWarning` since Python 3.6. In Python 3.8 it generates |
| a :exc:`SyntaxWarning` instead. |
| (Contributed by Serhiy Storchaka in :issue:`32912`.) |
| |
| * The compiler now produces a :exc:`SyntaxWarning` in some cases when a comma |
| is missed before tuple or list. For example:: |
| |
| data = [ |
| (1, 2, 3) # oops, missing comma! |
| (4, 5, 6) |
| ] |
| |
| (Contributed by Serhiy Storchaka in :issue:`15248`.) |
| |
| * Arithmetic operations between subclasses of :class:`datetime.date` or |
| :class:`datetime.datetime` and :class:`datetime.timedelta` objects now return |
| an instance of the subclass, rather than the base class. This also affects |
| the return type of operations whose implementation (directly or indirectly) |
| uses :class:`datetime.timedelta` arithmetic, such as |
| :meth:`datetime.datetime.astimezone`. |
| (Contributed by Paul Ganssle in :issue:`32417`.) |
| |
| * When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the |
| resulting :exc:`KeyboardInterrupt` exception is not caught, the Python process |
| now exits via a SIGINT signal or with the correct exit code such that the |
| calling process can detect that it died due to a Ctrl-C. Shells on POSIX |
| and Windows use this to properly terminate scripts in interactive sessions. |
| (Contributed by Google via Gregory P. Smith in :issue:`1054041`.) |
| |
| |
| New Modules |
| =========== |
| |
| * None yet. |
| |
| |
| Improved Modules |
| ================ |
| |
| * The :meth:`_asdict()` method for :func:`collections.namedtuple` now returns |
| a :class:`dict` instead of a :class:`collections.OrderedDict`. This works because |
| regular dicts have guaranteed ordering in since Python 3.7. If the extra |
| features of :class:`OrderedDict` are required, the suggested remediation is |
| to cast the result to the desired type: ``OrderedDict(nt._asdict())``. |
| (Contributed by Raymond Hettinger in :issue:`35864`.) |
| |
| * The :mod:`unicodedata` module has been upgraded to use the `Unicode 12.0.0 |
| <http://blog.unicode.org/2019/03/announcing-unicode-standard-version-120.html>`_ |
| release. |
| |
| |
| asyncio |
| ------- |
| |
| On Windows, the default event loop is now :class:`~asyncio.ProactorEventLoop`. |
| |
| |
| gettext |
| ------- |
| |
| Added :func:`~gettext.pgettext` and its variants. |
| (Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella in :issue:`2504`.) |
| |
| |
| gc |
| -- |
| |
| :func:`~gc.get_objects` can now receive an optional *generation* parameter |
| indicating a generation to get objects from. Contributed in |
| :issue:`36016` by Pablo Galindo. |
| |
| |
| gzip |
| ---- |
| |
| Added the *mtime* parameter to :func:`gzip.compress` for reproducible output. |
| (Contributed by Guo Ci Teo in :issue:`34898`.) |
| |
| |
| idlelib and IDLE |
| ---------------- |
| |
| Output over N lines (50 by default) is squeezed down to a button. |
| N can be changed in the PyShell section of the General page of the |
| Settings dialog. Fewer, but possibly extra long, lines can be squeezed by |
| right clicking on the output. Squeezed output can be expanded in place |
| by double-clicking the button or into the clipboard or a separate window |
| by right-clicking the button. (Contributed by Tal Einat in :issue:`1529353`.) |
| |
| The changes above have been backported to 3.7 maintenance releases. |
| |
| |
| json.tool |
| --------- |
| |
| Add option ``--json-lines`` to parse every input line as separate JSON object. |
| (Contributed by Weipeng Hong in :issue:`31553`.) |
| |
| |
| math |
| ---- |
| |
| Added new function :func:`math.dist` for computing Euclidean distance |
| between two points. (Contributed by Raymond Hettinger in :issue:`33089`.) |
| |
| Expanded the :func:`math.hypot` function to handle multiple dimensions. |
| Formerly, it only supported the 2-D case. |
| (Contributed by Raymond Hettinger in :issue:`33089`.) |
| |
| Added new function, :func:`math.prod`, as analogous function to :func:`sum` |
| that returns the product of a 'start' value (default: 1) times an iterable of |
| numbers. (Contributed by Pablo Galindo in :issue:`35606`) |
| |
| |
| os.path |
| ------- |
| |
| :mod:`os.path` functions that return a boolean result like |
| :func:`~os.path.exists`, :func:`~os.path.lexists`, :func:`~os.path.isdir`, |
| :func:`~os.path.isfile`, :func:`~os.path.islink`, and :func:`~os.path.ismount` |
| now return ``False`` instead of raising :exc:`ValueError` or its subclasses |
| :exc:`UnicodeEncodeError` and :exc:`UnicodeDecodeError` for paths that contain |
| characters or bytes unrepresentable at the OS level. |
| (Contributed by Serhiy Storchaka in :issue:`33721`.) |
| |
| :func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE` |
| environment variable and does not use :envvar:`HOME`, which is not normally set |
| for regular user accounts. |
| |
| |
| ncurses |
| ------- |
| |
| Added a new variable holding structured version information for the |
| underlying ncurses library: :data:`~curses.ncurses_version`. |
| (Contributed by Serhiy Storchaka in :issue:`31680`.) |
| |
| |
| pathlib |
| ------- |
| |
| :mod:`pathlib.Path` methods that return a boolean result like |
| :meth:`~pathlib.Path.exists()`, :meth:`~pathlib.Path.is_dir()`, |
| :meth:`~pathlib.Path.is_file()`, :meth:`~pathlib.Path.is_mount()`, |
| :meth:`~pathlib.Path.is_symlink()`, :meth:`~pathlib.Path.is_block_device()`, |
| :meth:`~pathlib.Path.is_char_device()`, :meth:`~pathlib.Path.is_fifo()`, |
| :meth:`~pathlib.Path.is_socket()` now return ``False`` instead of raising |
| :exc:`ValueError` or its subclass :exc:`UnicodeEncodeError` for paths that |
| contain characters unrepresentable at the OS level. |
| (Contributed by Serhiy Storchaka in :issue:`33721`.) |
| |
| |
| shutil |
| ------ |
| |
| :func:`shutil.copytree` now accepts a new ``dirs_exist_ok`` keyword argument. |
| (Contributed by Josh Bronson in :issue:`20849`.) |
| |
| |
| ssl |
| --- |
| |
| Added :attr:`SSLContext.post_handshake_auth` to enable and |
| :meth:`ssl.SSLSocket.verify_client_post_handshake` to initiate TLS 1.3 |
| post-handshake authentication. |
| (Contributed by Christian Heimes in :issue:`34670`.) |
| |
| |
| statistics |
| ---------- |
| |
| Added :func:`statistics.fmean` as a faster, floating point variant of |
| :func:`statistics.mean()`. (Contributed by Raymond Hettinger and |
| Steven D'Aprano in :issue:`35904`.) |
| |
| Added :func:`statistics.multimode` that returns a list of the most |
| common values. (Contributed by Raymond Hettinger in :issue:`35892`.) |
| |
| Added :class:`statistics.NormalDist`, a tool for creating |
| and manipulating normal distributions of a random variable. |
| (Contributed by Raymond Hettinger in :issue:`36018`.) |
| |
| :: |
| |
| >>> temperature_feb = NormalDist.from_samples([4, 12, -3, 2, 7, 14]) |
| >>> temperature_feb |
| NormalDist(mu=6.0, sigma=6.356099432828281) |
| |
| >>> temperature_feb.cdf(3) # Chance of being under 3 degrees |
| 0.3184678262814532 |
| >>> # Relative chance of being 7 degrees versus 10 degrees |
| >>> temperature_feb.pdf(7) / temperature_feb.pdf(10) |
| 1.2039930378537762 |
| |
| >>> el_nino = NormalDist(4, 2.5) |
| >>> temperature_feb += el_nino # Add in a climate effect |
| >>> temperature_feb |
| NormalDist(mu=10.0, sigma=6.830080526611674) |
| |
| >>> temperature_feb * (9/5) + 32 # Convert to Fahrenheit |
| NormalDist(mu=50.0, sigma=12.294144947901014) |
| >>> temperature_feb.samples(3) # Generate random samples |
| [7.672102882379219, 12.000027119750287, 4.647488369766392] |
| |
| |
| tokenize |
| -------- |
| |
| The :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token when |
| provided with input that does not have a trailing new line. This behavior |
| now matches what the C tokenizer does internally. |
| (Contributed by Ammar Askar in :issue:`33899`.) |
| |
| tkinter |
| ------- |
| |
| Added methods :meth:`~tkinter.Spinbox.selection_from`, |
| :meth:`~tkinter.Spinbox.selection_present`, |
| :meth:`~tkinter.Spinbox.selection_range` and |
| :meth:`~tkinter.Spinbox.selection_to` |
| in the :class:`tkinter.Spinbox` class. |
| (Contributed by Juliette Monsel in :issue:`34829`.) |
| |
| Added method :meth:`~tkinter.Canvas.moveto` |
| in the :class:`tkinter.Canvas` class. |
| (Contributed by Juliette Monsel in :issue:`23831`.) |
| |
| time |
| ---- |
| |
| Added new clock :data:`~time.CLOCK_UPTIME_RAW` for macOS 10.12. |
| (Contributed by Joannah Nanjekye in :issue:`35702`.) |
| |
| unicodedata |
| ----------- |
| |
| * New function :func:`~unicodedata.is_normalized` can be used to verify a string |
| is in a specific normal form. (Contributed by Max Belanger and David Euresti in |
| :issue:`32285`). |
| |
| unittest |
| -------- |
| |
| * Added :func:`~unittest.addModuleCleanup()` and |
| :meth:`~unittest.TestCase.addClassCleanup()` to unittest to support |
| cleanups for :func:`~unittest.setUpModule()` and |
| :meth:`~unittest.TestCase.setUpClass()`. |
| (Contributed by Lisa Roach in :issue:`24412`.) |
| |
| venv |
| ---- |
| |
| * :mod:`venv` now includes an ``Activate.ps1`` script on all platforms for |
| activating virtual environments under PowerShell Core 6.1. |
| (Contributed by Brett Cannon in :issue:`32718`.) |
| |
| xml |
| --- |
| |
| * As mitigation against DTD and external entity retrieval, the |
| :mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process |
| external entities by default. |
| (Contributed by Christian Heimes in :issue:`17239`.) |
| |
| |
| Optimizations |
| ============= |
| |
| * The :mod:`subprocess` module can now use the :func:`os.posix_spawn` function |
| in some cases for better performance. Currently, it is only used on macOS |
| and Linux (using glibc 2.24 or newer) if all these conditions are met: |
| |
| * *close_fds* is false; |
| * *preexec_fn*, *pass_fds*, *cwd* and *start_new_session* parameters |
| are not set; |
| * the *executable* path contains a directory. |
| |
| * :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`, |
| :func:`shutil.copytree` and :func:`shutil.move` use platform-specific |
| "fast-copy" syscalls on Linux, macOS and Solaris in order to copy the file |
| more efficiently. |
| "fast-copy" means that the copying operation occurs within the kernel, |
| avoiding the use of userspace buffers in Python as in |
| "``outfd.write(infd.read())``". |
| On Windows :func:`shutil.copyfile` uses a bigger default buffer size (1 MiB |
| instead of 16 KiB) and a :func:`memoryview`-based variant of |
| :func:`shutil.copyfileobj` is used. |
| The speedup for copying a 512 MiB file within the same partition is about |
| +26% on Linux, +50% on macOS and +40% on Windows. Also, much less CPU cycles |
| are consumed. |
| See :ref:`shutil-platform-dependent-efficient-copy-operations` section. |
| (Contributed by Giampaolo Rodola' in :issue:`33671`.) |
| |
| * :func:`shutil.copytree` uses :func:`os.scandir` function and all copy |
| functions depending from it use cached :func:`os.stat` values. The speedup |
| for copying a directory with 8000 files is around +9% on Linux, +20% on |
| Windows and +30% on a Windows SMB share. Also the number of :func:`os.stat` |
| syscalls is reduced by 38% making :func:`shutil.copytree` especially faster |
| on network filesystems. (Contributed by Giampaolo Rodola' in :issue:`33695`.) |
| |
| * The default protocol in the :mod:`pickle` module is now Protocol 4, |
| first introduced in Python 3.4. It offers better performance and smaller |
| size compared to Protocol 3 available since Python 3.0. |
| |
| * Removed one ``Py_ssize_t`` member from ``PyGC_Head``. All GC tracked |
| objects (e.g. tuple, list, dict) size is reduced 4 or 8 bytes. |
| (Contributed by Inada Naoki in :issue:`33597`) |
| |
| * :class:`uuid.UUID` now uses ``__slots__`` to reduce its memory footprint. |
| |
| * Improved performance of :func:`operator.itemgetter` by 33%. Optimized |
| argument handling and added a fast path for the common case of a single |
| non-negative integer index into a tuple (which is the typical use case in |
| the standard library). (Contributed by Raymond Hettinger in |
| :issue:`35664`.) |
| |
| * Sped-up field lookups in :func:`collections.namedtuple`. They are now more |
| than two times faster, making them the fastest form of instance variable |
| lookup in Python. (Contributed by Raymond Hettinger, Pablo Galindo, and |
| Joe Jevnik, Serhiy Storchaka in :issue:`32492`.) |
| |
| * The :class:`list` constructor does not overallocate the internal item buffer |
| if the input iterable has a known length (the input implements ``__len__``). |
| This makes the created list 12% smaller on average. (Contributed by |
| Raymond Hettinger and Pablo Galindo in :issue:`33234`.) |
| |
| * Doubled the speed of class variable writes. When a non-dunder attribute |
| was updated, there was an unnecessary call to update slots. |
| (Contributed by Stefan Behnel, Pablo Galindo Salgado, Raymond Hettinger, |
| Neil Schemenauer, and Serhiy Storchaka in :issue:`36012`.) |
| |
| * Reduced an overhead of converting arguments passed to many builtin functions |
| and methods. This sped up calling some simple builtin functions and |
| methods up to 20--50%. (Contributed by Serhiy Storchaka in :issue:`23867`, |
| :issue:`35582` and :issue:`36127`.) |
| |
| |
| Build and C API Changes |
| ======================= |
| |
| * The :c:func:`PyByteArray_Init` and :c:func:`PyByteArray_Fini` functions have |
| been removed. They did nothing since Python 2.7.4 and Python 3.2.0, were |
| excluded from the limited API (stable ABI), and were not documented. |
| |
| * The result of :c:func:`PyExceptionClass_Name` is now of type |
| ``const char *`` rather of ``char *``. |
| (Contributed by Serhiy Storchaka in :issue:`33818`.) |
| |
| * The duality of ``Modules/Setup.dist`` and ``Modules/Setup`` has been |
| removed. Previously, when updating the CPython source tree, one had |
| to manually copy ``Modules/Setup.dist`` (inside the source tree) to |
| ``Modules/Setup`` (inside the build tree) in order to reflect any changes |
| upstream. This was of a small benefit to packagers at the expense of |
| a frequent annoyance to developers following CPython development, as |
| forgetting to copy the file could produce build failures. |
| |
| Now the build system always reads from ``Modules/Setup`` inside the source |
| tree. People who want to customize that file are encouraged to maintain |
| their changes in a git fork of CPython or as patch files, as they would do |
| for any other change to the source tree. |
| |
| (Contributed by Antoine Pitrou in :issue:`32430`.) |
| |
| * Functions that convert Python number to C integer like |
| :c:func:`PyLong_AsLong` and argument parsing functions like |
| :c:func:`PyArg_ParseTuple` with integer converting format units like ``'i'`` |
| will now use the :meth:`~object.__index__` special method instead of |
| :meth:`~object.__int__`, if available. The deprecation warning will be |
| emitted for objects with the ``__int__()`` method but without the |
| ``__index__()`` method (like :class:`~decimal.Decimal` and |
| :class:`~fractions.Fraction`). :c:func:`PyNumber_Check` will now return |
| ``1`` for objects implementing ``__index__()``. |
| (Contributed by Serhiy Storchaka in :issue:`36048`.) |
| |
| |
| Deprecated |
| ========== |
| |
| * Deprecated methods ``getchildren()`` and ``getiterator()`` in |
| the :mod:`~xml.etree.ElementTree` module emit now a |
| :exc:`DeprecationWarning` instead of :exc:`PendingDeprecationWarning`. |
| They will be removed in Python 3.9. |
| (Contributed by Serhiy Storchaka in :issue:`29209`.) |
| |
| * Passing an object that is not an instance of |
| :class:`concurrent.futures.ThreadPoolExecutor` to |
| :meth:`asyncio.loop.set_default_executor()` is |
| deprecated and will be prohibited in Python 3.9. |
| (Contributed by Elvis Pranskevichus in :issue:`34075`.) |
| |
| * The :meth:`__getitem__` methods of :class:`xml.dom.pulldom.DOMEventStream`, |
| :class:`wsgiref.util.FileWrapper` and :class:`fileinput.FileInput` have been |
| deprecated. |
| |
| Implementations of these methods have been ignoring their *index* parameter, |
| and returning the next item instead. |
| |
| (Contributed by Berker Peksag in :issue:`9372`.) |
| |
| * :mod:`ast` classes ``Num``, ``Str``, ``Bytes``, ``NameConstant`` and |
| ``Ellipsis`` are considered deprecated and will be removed in future Python |
| versions. :class:`~ast.Constant` should be used instead. |
| (Contributed by Serhiy Storchaka in :issue:`32892`.) |
| |
| * The following functions and methods are deprecated in the :mod:`gettext` |
| module: :func:`~gettext.lgettext`, :func:`~gettext.ldgettext`, |
| :func:`~gettext.lngettext` and :func:`~gettext.ldngettext`. |
| They return encoded bytes, and it's possible that you will get unexpected |
| Unicode-related exceptions if there are encoding problems with the |
| translated strings. It's much better to use alternatives which return |
| Unicode strings in Python 3. These functions have been broken for a long time. |
| |
| Function :func:`~gettext.bind_textdomain_codeset`, methods |
| :meth:`~gettext.NullTranslations.output_charset` and |
| :meth:`~gettext.NullTranslations.set_output_charset`, and the *codeset* |
| parameter of functions :func:`~gettext.translation` and |
| :func:`~gettext.install` are also deprecated, since they are only used for |
| for the ``l*gettext()`` functions. |
| |
| (Contributed by Serhiy Storchaka in :issue:`33710`.) |
| |
| * The :meth:`~threading.Thread.isAlive()` method of :class:`threading.Thread` has been deprecated. |
| (Contributed by Dong-hee Na in :issue:`35283`.) |
| |
| * Many builtin and extension functions that take integer arguments will |
| now emit a deprecation warning for :class:`~decimal.Decimal`\ s, |
| :class:`~fractions.Fraction`\ s and any other objects that can be converted |
| to integers only with a loss (e.g. that have the :meth:`~object.__int__` |
| method but do not have the :meth:`~object.__index__` method). In future |
| version they will be errors. |
| (Contributed by Serhiy Storchaka in :issue:`36048`.) |
| |
| |
| API and Feature Removals |
| ======================== |
| |
| The following features and APIs have been removed from Python 3.8: |
| |
| * The :mod:`macpath` module, deprecated in Python 3.7, has been removed. |
| (Contributed by Victor Stinner in :issue:`35471`.) |
| |
| * The function :func:`platform.popen` has been removed, it was deprecated since |
| Python 3.3: use :func:`os.popen` instead. |
| |
| * The ``pyvenv`` script has been removed in favor of ``python3.8 -m venv`` |
| to help eliminate confusion as to what Python interpreter the ``pyvenv`` |
| script is tied to. (Contributed by Brett Cannon in :issue:`25427`.) |
| |
| * ``parse_qs``, ``parse_qsl``, and ``escape`` are removed from :mod:`cgi` |
| module. They are deprecated from Python 3.2 or older. |
| |
| * ``filemode`` function is removed from :mod:`tarfile` module. |
| It is not documented and deprecated since Python 3.3. |
| |
| * The :class:`~xml.etree.ElementTree.XMLParser` constructor no longer accepts |
| the *html* argument. It never had effect and was deprecated in Python 3.4. |
| All other parameters are now :ref:`keyword-only <keyword-only_parameter>`. |
| (Contributed by Serhiy Storchaka in :issue:`29209`.) |
| |
| * Removed the ``doctype()`` method of :class:`~xml.etree.ElementTree.XMLParser`. |
| (Contributed by Serhiy Storchaka in :issue:`29209`.) |
| |
| * "unicode_internal" codec is removed. |
| (Contributed by Inada Naoki in :issue:`36297`.) |
| |
| |
| Porting to Python 3.8 |
| ===================== |
| |
| This section lists previously described changes and other bugfixes |
| that may require changes to your code. |
| |
| |
| Changes in Python behavior |
| -------------------------- |
| |
| * Yield expressions (both ``yield`` and ``yield from`` clauses) are now disallowed |
| in comprehensions and generator expressions (aside from the iterable expression |
| in the leftmost :keyword:`!for` clause). |
| (Contributed by Serhiy Storchaka in :issue:`10544`.) |
| |
| * The compiler now produces a :exc:`SyntaxWarning` when identity checks |
| (``is`` and ``is not``) are used with certain types of literals |
| (e.g. strings, ints). These can often work by accident in CPython, |
| but are not guaranteed by the language spec. The warning advises users |
| to use equality tests (``==`` and ``!=``) instead. |
| (Contributed by Serhiy Storchaka in :issue:`34850`.) |
| |
| |
| Changes in the Python API |
| ------------------------- |
| |
| * The function :func:`platform.popen` has been removed, it was deprecated since |
| Python 3.3: use :func:`os.popen` instead. |
| |
| * The :func:`statistics.mode` function no longer raises an exception |
| when given multimodal data. Instead, it returns the first mode |
| encountered in the input data. (Contributed by Raymond Hettinger |
| in :issue:`35892`.) |
| |
| * The :meth:`~tkinter.ttk.Treeview.selection` method of the |
| :class:`tkinter.ttk.Treeview` class no longer takes arguments. Using it with |
| arguments for changing the selection was deprecated in Python 3.6. Use |
| specialized methods like :meth:`~tkinter.ttk.Treeview.selection_set` for |
| changing the selection. (Contributed by Serhiy Storchaka in :issue:`31508`.) |
| |
| * The :meth:`writexml`, :meth:`toxml` and :meth:`toprettyxml` methods of the |
| :mod:`xml.dom.minidom` module, and :mod:`xml.etree` now preserve the attribute |
| order specified by the user. |
| (Contributed by Diego Rojas and Raymond Hettinger in :issue:`34160`.) |
| |
| * A :mod:`dbm.dumb` database opened with flags ``'r'`` is now read-only. |
| :func:`dbm.dumb.open` with flags ``'r'`` and ``'w'`` no longer creates |
| a database if it does not exist. |
| (Contributed by Serhiy Storchaka in :issue:`32749`.) |
| |
| * The ``doctype()`` method defined in a subclass of |
| :class:`~xml.etree.ElementTree.XMLParser` will no longer be called and will |
| cause emitting a :exc:`RuntimeWarning` instead of a :exc:`DeprecationWarning`. |
| Define the :meth:`doctype() <xml.etree.ElementTree.TreeBuilder.doctype>` |
| method on a target for handling an XML doctype declaration. |
| (Contributed by Serhiy Storchaka in :issue:`29209`.) |
| |
| * A :exc:`RuntimeError` is now raised when the custom metaclass doesn't |
| provide the ``__classcell__`` entry in the namespace passed to |
| ``type.__new__``. A :exc:`DeprecationWarning` was emitted in Python |
| 3.6--3.7. (Contributed by Serhiy Storchaka in :issue:`23722`.) |
| |
| * The :class:`cProfile.Profile` class can now be used as a context |
| manager. (Contributed by Scott Sanderson in :issue:`29235`.) |
| |
| * :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`, |
| :func:`shutil.copytree` and :func:`shutil.move` use platform-specific |
| "fast-copy" syscalls (see |
| :ref:`shutil-platform-dependent-efficient-copy-operations` section). |
| |
| * :func:`shutil.copyfile` default buffer size on Windows was changed from |
| 16 KiB to 1 MiB. |
| |
| * ``PyGC_Head`` struct is changed completely. All code touched the |
| struct member should be rewritten. (See :issue:`33597`) |
| |
| * The ``PyInterpreterState`` struct has been moved into the "internal" |
| header files (specifically Include/internal/pycore_pystate.h). An |
| opaque ``PyInterpreterState`` is still available as part of the public |
| API (and stable ABI). The docs indicate that none of the struct's |
| fields are public, so we hope no one has been using them. However, |
| if you do rely on one or more of those private fields and have no |
| alternative then please open a BPO issue. We'll work on helping |
| you adjust (possibly including adding accessor functions to the |
| public API). (See :issue:`35886`.) |
| |
| * Asyncio tasks can now be named, either by passing the ``name`` keyword |
| argument to :func:`asyncio.create_task` or |
| the :meth:`~asyncio.loop.create_task` event loop method, or by |
| calling the :meth:`~asyncio.Task.set_name` method on the task object. The |
| task name is visible in the ``repr()`` output of :class:`asyncio.Task` and |
| can also be retrieved using the :meth:`~asyncio.Task.get_name` method. |
| |
| * The :meth:`mmap.flush() <mmap.mmap.flush>` method now returns ``None`` on |
| success and raises an exception on error under all platforms. Previously, |
| its behavior was platform-depended: a nonzero value was returned on success; |
| zero was returned on error under Windows. A zero value was returned on |
| success; an exception was raised on error under Unix. |
| (Contributed by Berker Peksag in :issue:`2122`.) |
| |
| * The function :func:`math.factorial` no longer accepts arguments that are not |
| int-like. (Contributed by Pablo Galindo in :issue:`33083`.) |
| |
| * :mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process |
| external entities by default. |
| (Contributed by Christian Heimes in :issue:`17239`.) |
| |
| * Deleting a key from a read-only :mod:`dbm` database (:mod:`dbm.dumb`, |
| :mod:`dbm.gnu` or :mod:`dbm.ndbm`) raises :attr:`error` (:exc:`dbm.dumb.error`, |
| :exc:`dbm.gnu.error` or :exc:`dbm.ndbm.error`) instead of :exc:`KeyError`. |
| (Contributed by Xiang Zhang in :issue:`33106`.) |
| |
| * :func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE` |
| environment variable and does not use :envvar:`HOME`, which is not normally |
| set for regular user accounts. |
| |
| |
| CPython bytecode changes |
| ------------------------ |
| |
| * The interpreter loop has been simplified by moving the logic of unrolling |
| the stack of blocks into the compiler. The compiler emits now explicit |
| instructions for adjusting the stack of values and calling the |
| cleaning-up code for :keyword:`break`, :keyword:`continue` and |
| :keyword:`return`. |
| |
| Removed opcodes :opcode:`BREAK_LOOP`, :opcode:`CONTINUE_LOOP`, |
| :opcode:`SETUP_LOOP` and :opcode:`SETUP_EXCEPT`. Added new opcodes |
| :opcode:`ROT_FOUR`, :opcode:`BEGIN_FINALLY`, :opcode:`CALL_FINALLY` and |
| :opcode:`POP_FINALLY`. Changed the behavior of :opcode:`END_FINALLY` |
| and :opcode:`WITH_CLEANUP_START`. |
| |
| (Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka in |
| :issue:`17611`.) |
| |
| * Added new opcode :opcode:`END_ASYNC_FOR` for handling exceptions raised |
| when awaiting a next item in an :keyword:`async for` loop. |
| (Contributed by Serhiy Storchaka in :issue:`33041`.) |
| |
| |
| Demos and Tools |
| --------------- |
| |
| * Added a benchmark script for timing various ways to access variables: |
| ``Tools/scripts/var_access_benchmark.py``. |
| (Contributed by Raymond Hettinger in :issue:`35884`.) |