612 lines
24 KiB
ReStructuredText
612 lines
24 KiB
ReStructuredText
****************************
|
|
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`.)
|
|
|
|
|
|
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`.)
|
|
|
|
|
|
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`.)
|
|
|
|
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`.)
|
|
|
|
|
|
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`.)
|
|
|
|
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
|
|
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`.)
|
|
|
|
|
|
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`.)
|
|
|
|
|
|
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`.)
|
|
|
|
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`.)
|
|
|
|
|
|
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 :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`.)
|
|
|
|
* 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`)
|
|
|
|
* 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`.)
|
|
|
|
|
|
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`.)
|