**************************** What's New In Python 3.6 **************************** :Release: |release| :Date: |today| .. 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 3.6, compared to 3.5. For full details, see the :source:`Misc/NEWS` file. .. note:: Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.6 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 3.6. Brevity is key. * PEP 498: :ref:`Formatted string literals ` .. PEP-sized items next. .. _pep-4XX: .. PEP 4XX: Virtual Environments .. ============================= .. (Implemented by Foo Bar.) .. .. seealso:: :pep:`4XX` - Python Virtual Environments PEP written by Carl Meyer .. _whatsnew-fstrings: PEP 498: Formatted string literals ---------------------------------- Formatted string literals are a new kind of string literal, prefixed with ``'f'``. They are similar to the format strings accepted by :meth:`str.format`. They contain replacement fields surrounded by curly braces. The replacement fields are expressions, which are evaluated at run time, and then formatted using the :func:`format` protocol. >>> name = "Fred" >>> f"He said his name is {name}." 'He said his name is Fred.' See :pep:`498` and the main documentation at :ref:`f-strings`. Other Language Changes ====================== * None yet. New Modules =========== * None yet. Improved Modules ================ datetime -------- The :meth:`datetime.strftime() ` and :meth:`date.strftime() ` methods now support ISO 8601 date directives ``%G``, ``%u`` and ``%V``. (Contributed by Ashley Anderson in :issue:`12006`.) os -- A new :meth:`~os.scandir.close` method allows explicitly closing a :func:`~os.scandir` iterator. The :func:`~os.scandir` iterator now supports the :term:`context manager` protocol. If a :func:`scandir` iterator is neither exhausted nor explicitly closed a :exc:`ResourceWarning` will be emitted in its destructor. (Contributed by Serhiy Storchaka in :issue:`25994`.) pickle ------ Objects that need calling ``__new__`` with keyword arguments can now be pickled using :ref:`pickle protocols ` older than protocol version 4. Protocol version 4 already supports this case. (Contributed by Serhiy Storchaka in :issue:`24164`.) rlcompleter ----------- Private and special attribute names now are omitted unless the prefix starts with underscores. A space or a colon is added after some completed keywords. (Contributed by Serhiy Storchaka in :issue:`25011` and :issue:`25209`.) Names of most attributes listed by :func:`dir` are now completed. Previously, names of properties and slots which were not yet created on an instance were excluded. (Contributed by Martin Panter in :issue:`25590`.) telnetlib --------- :class:`~telnetlib.Telnet` is now a context manager (contributed by Stéphane Wirtel in :issue:`25485`). urllib.robotparser ------------------ :class:`~urllib.robotparser.RobotFileParser` now supports the ``Crawl-delay`` and ``Request-rate`` extensions. (Contributed by Nikolay Bogoychev in :issue:`16099`.) zipfile ------- A new :meth:`ZipInfo.from_file() ` class method allows making a :class:`~zipfile.ZipInfo` instance from a filesystem file. A new :meth:`ZipInfo.is_dir() ` method can be used to check if the :class:`~zipfile.ZipInfo` instance represents a directory. (Contributed by Thomas Kluyver in :issue:`26039`.) zlib ---- The :func:`~zlib.compress` function now accepts keyword arguments. (Contributed by Aviv Palivoda in :issue:`26243`.) Optimizations ============= * The ASCII decoder is now up to 60 times as fast for error handlers ``surrogateescape``, ``ignore`` and ``replace`` (Contributed by Victor Stinner in :issue:`24870`). * The ASCII and the Latin1 encoders are now up to 3 times as fast for the error handler ``surrogateescape`` (Contributed by Victor Stinner in :issue:`25227`). * The UTF-8 encoder is now up to 75 times as fast for error handlers ``ignore``, ``replace``, ``surrogateescape``, ``surrogatepass`` (Contributed by Victor Stinner in :issue:`25267`). * The UTF-8 decoder is now up to 15 times as fast for error handlers ``ignore``, ``replace`` and ``surrogateescape`` (Contributed by Victor Stinner in :issue:`25301`). * ``bytes % args`` is now up to 2 times faster. (Contributed by Victor Stinner in :issue:`25349`). * ``bytearray % args`` is now between 2.5 and 5 times faster. (Contributed by Victor Stinner in :issue:`25399`). * Optimize :meth:`bytes.fromhex` and :meth:`bytearray.fromhex`: they are now between 2x and 3.5x faster. (Contributed by Victor Stinner in :issue:`25401`). Build and C API Changes ======================= * New :c:func:`Py_FinalizeEx` API which indicates if flushing buffered data failed (:issue:`5319`). Deprecated ========== New Keywords ------------ ``async`` and ``await`` are not recommended to be used as variable, class, function or module names. Introduced by :pep:`492` in Python 3.5, they will become proper keywords in Python 3.7. Deprecated Python modules, functions and methods ------------------------------------------------ * :meth:`importlib.machinery.SourceFileLoader` and :meth:`importlib.machinery.SourcelessFileLoader` are now deprecated. They were the only remaining implementations of :meth:`importlib.abc.Loader.load_module` in :mod:`importlib` that had not been deprecated in previous versions of Python in favour of :meth:`importlib.abc.Loader.exec_module`. Deprecated functions and types of the C API ------------------------------------------- * None yet. Deprecated features ------------------- * The ``pyvenv`` script has been deprecated in favour of ``python3 -m venv``. This prevents confusion as to what Python interpreter ``pyvenv`` is connected to and thus what Python interpreter will be used by the virtual environment. (Contributed by Brett Cannon in :issue:`25154`.) * When performing a relative import, falling back on ``__name__`` and ``__path__`` from the calling module when ``__spec__`` or ``__package__`` are not defined now raises an :exc:`ImportWarning`. (Contributed by Rose Ames in :issue:`25791`.) Deprecated Python behavior -------------------------- * Raising the :exc:`StopIteration` exception inside a generator will now generate a :exc:`DeprecationWarning`, and will trigger a :exc:`RuntimeError` in Python 3.7. See :ref:`whatsnew-pep-479` for details. Removed ======= API and Feature Removals ------------------------ * ``inspect.getmoduleinfo()`` was removed (was deprecated since CPython 3.3). :func:`inspect.getmodulename` should be used for obtaining the module name for a given path. * ``traceback.Ignore`` class and ``traceback.usage``, ``traceback.modname``, ``traceback.fullmodname``, ``traceback.find_lines_from_code``, ``traceback.find_lines``, ``traceback.find_strings``, ``traceback.find_executable_lines`` methods were removed from the :mod:`traceback` module. They were undocumented methods deprecated since Python 3.2 and equivalent functionality is available from private methods. Porting to Python 3.6 ===================== This section lists previously described changes and other bugfixes that may require changes to your code. Changes in the Python API ------------------------- * The format of the ``co_lnotab`` attribute of code objects changed to support negative line number delta. By default, Python does not emit bytecode with negative line number delta. Functions using ``frame.f_lineno``, ``PyFrame_GetLineNumber()`` or ``PyCode_Addr2Line()`` are not affected. Functions decoding directly ``co_lnotab`` should be updated to use a signed 8-bit integer type for the line number delta, but it's only required to support applications using negative line number delta. See ``Objects/lnotab_notes.txt`` for the ``co_lnotab`` format and how to decode it, and see the :pep:`511` for the rationale. * The functions in the :mod:`compileall` module now return booleans instead of ``1`` or ``0`` to represent success or failure, respectively. Thanks to booleans being a subclass of integers, this should only be an issue if you were doing identity checks for ``1`` or ``0``. See :issue:`25768`. * Reading the :attr:`~urllib.parse.SplitResult.port` attribute of :func:`urllib.parse.urlsplit` and :func:`~urllib.parse.urlparse` results now raises :exc:`ValueError` for out-of-range values, rather than returning :const:`None`. See :issue:`20059`. * The :mod:`imp` module now raises a :exc:`DeprecationWarning` instead of :exc:`PendingDeprecationWarning`. * The following modules have had missing APIs added to their :attr:`__all__` attributes to match the documented APIs: :mod:`calendar`, :mod:`csv`, :mod:`enum`, :mod:`fileinput`, :mod:`ftplib`, :mod:`logging`, :mod:`optparse`, :mod:`tarfile`, :mod:`threading` and :mod:`wave`. This means they will export new symbols when ``import *`` is used. See :issue:`23883`. * When performing a relative import, if ``__package__`` does not compare equal to ``__spec__.parent`` then :exc:`ImportWarning` is raised. (Contributed by Brett Cannon in :issue:`25791`.) * When a relative import is performed and no parent package is known, then :exc:`ImportError` will be raised. Previously, :exc:`SystemError` could be raised. (Contributed by Brett Cannon in :issue:`18018`.) * Servers based on the :mod:`socketserver` module, including those defined in :mod:`http.server`, :mod:`xmlrpc.server` and :mod:`wsgiref.simple_server`, now only catch exceptions derived from :exc:`Exception`. Therefore if a request handler raises an exception like :exc:`SystemExit` or :exc:`KeyboardInterrupt`, :meth:`~socketserver.BaseServer.handle_error` is no longer called, and the exception will stop a single-threaded server. (Contributed by Martin Panter in :issue:`23430`.) Changes in the C API -------------------- * :c:func:`Py_Exit` (and the main interpreter) now override the exit status with 120 if flushing buffered data failed. See :issue:`5319`.