cpython/Doc/whatsnew/3.5.rst

****************************
  What's New In Python 3.5
****************************

: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 3.5, compared to 3.4.

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 3.5 moves towards
   release, so it's worth checking back even after reading earlier versions.


.. seealso::

    :pep:`478` - Python 3.5 Release Schedule


Summary -- Release highlights
=============================

.. This section singles out the most important changes in Python 3.3.
   Brevity is key.

New syntax features:

* None yet.

New library modules:

* None yet.

New built-in features:

* None yet.

Implementation improvements:

* When the ``LC_TYPE`` locale is the POSIX locale (``C`` locale),
  :py:data:`sys.stdin` and :py:data:`sys.stdout` are now using the
  ``surrogateescape`` error handler, instead of the ``strict`` error handler
  (:issue:`19977`).

Significantly Improved Library Modules:

* None yet.

Security improvements:

* None yet.

Please read on for a comprehensive list of user-facing changes.


.. 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




Other Language Changes
======================

Some smaller changes made to the core Python language are:

* Added the ``'namereplace'`` error handlers.  The ``'backslashreplace'``
  error handlers now works with decoding and translating.
  (Contributed by Serhiy Storchaka in :issue:`19676` and :issue:`22286`.)



New Modules
===========

.. module name
.. -----------

* None yet.


Improved Modules
================

code
----

* The :func:`code.InteractiveInterpreter.showtraceback` method now prints
  the full chained traceback, just like the interactive interpreter.
  (Contributed by Claudiu.Popa in :issue:`17442`.)

compileall
----------

* :func:`compileall.compile_dir` and :mod:`compileall`'s command-line interface
  can now do parallel bytecode compilation.
  (Contributed by Claudiu Popa in :issue:`16104`.)

contextlib
----------

* The new :func:`contextlib.redirect_stderr` context manager(similar to
  :func:`contextlib.redirect_stdout`) makes it easier for utility scripts to
  handle inflexible APIs that write their output to :data:`sys.stderr` and
  don't provide any options to redirect it.
  (Contributed by Berker Peksag in :issue:`22389`.)

doctest
-------

* :func:`doctest.DocTestSuite` returns an empty :class:`unittest.TestSuite` if
  *module* contains no docstrings instead of raising :exc:`ValueError`.
  (Contributed by Glenn Jones in :issue:`15916`.)

glob
----

* :func:`~glob.iglob` and :func:`~glob.glob` now support recursive search in
  subdirectories using the "``**``" pattern.
  (Contributed by Serhiy Storchaka in :issue:`13968`.)

imaplib
-------

* :class:`IMAP4` now supports the context management protocol.  When used in a
  :keyword:`with` statement, the IMAP4 ``LOGOUT`` command will be called
  automatically at the end of the block.  (Contributed by Tarek Ziadé and
  Serhiy Storchaka in :issue:`4972`.)

imghdr
------

* :func:`~imghdr.what` now recognizes the `OpenEXR <http://www.openexr.com>`_
  format.  (Contributed by Martin vignali and Cladui Popa in :issue:`20295`.)

importlib
---------

* :class:`importlib.util.LazyLoader` allows for the lazy loading of modules in
  applications where startup time is paramount.
  (Contributed by Brett Cannon in :issue:`17621`.)

* :func:`importlib.abc.InspectLoader.source_to_code` is now a
  static method to make it easier to work with source code in a string.
  With a module object that you want to initialize you can then use
  ``exec(code, module.__dict__)`` to execute the code in the module.

* :func:`importlib.util.module_from_spec` is now the preferred way to create a
  new module. Compared to :class:`types.ModuleType`, this new function will set
  the various import-controlled attributes based on the passed-in spec object.

inspect
-------

* :class:`inspect.Signature` and :class:`inspect.Parameter` are now
  picklable and hashable.  (Contributed by Yury Selivanov in :issue:`20726`
  and :issue:`20334`.)

* New class method :meth:`inspect.Signature.from_callable`, which makes
  subclassing of :class:`~inspect.Signature` easier.  (Contributed
  by Yury Selivanov and Eric Snow in :issue:`17373`.)

ipaddress
---------

* :class:`ipaddress.IPv4Network` and :class:`ipaddress.IPv6Network` now
  accept an ``(address, netmask)`` tuple argument, so as to easily construct
  network objects from existing addresses.  (Contributed by Peter Moody
  and Antoine Pitrou in :issue:`16531`.)

json
----

* The output of :mod:`json.tool` command line interface is now in the same
  order as the input. Use the :option:`--sort-keys` option to sort the output
  of dictionaries alphabetically by key.  (Contributed by Berker Peksag in
  :issue:`21650`.)

* JSON decoder now raises :exc:`json.JSONDecodeError` instead of
  :exc:`ValueError`.   (Contributed by Serhiy Storchaka in :issue:`19361`.)

os
--

* :class:`os.stat_result` now has a :attr:`~os.stat_result.st_file_attributes`
  attribute on Windows.  (Contributed by Ben Hoyt in :issue:`21719`.)

re
--

* Number of capturing groups in regular expression is no longer limited by 100.
  (Contributed by Serhiy Storchaka in :issue:`22437`.)

* Now unmatched groups are replaced with empty strings in :func:`re.sub`
  and :func:`re.subn`.  (Contributed by Serhiy Storchaka in :issue:`1519638`.)

math
----

* :data:`math.inf` and :data:`math.nan` constants added.  (Contributed by Mark
  Dickinson in :issue:`23185`.)

shutil
------

* :func:`~shutil.move` now accepts a *copy_function* argument, allowing,
  for example, :func:`~shutil.copy` to be used instead of the default
  :func:`~shutil.copy2` if there is a need to ignore metadata.  (Contributed by
  Claudiu Popa in :issue:`19840`.)

signal
------

* Different constants of :mod:`signal` module are now enumeration values using
  the :mod:`enum` module. This allows meaningful names to be printed during
  debugging, instead of integer “magic numbers”.  (Contributed by Giampaolo
  Rodola' in :issue:`21076`.)

smtpd
-----

* Both :class:`~smtpd.SMTPServer` and :class:`smtpd.SMTPChannel` now accept a
  *decode_data* keyword to determine if the DATA portion of the SMTP
  transaction is decoded using the ``utf-8`` codec or is instead provided to
  :meth:`~smtpd.SMTPServer.process_message` as a byte string.  The default
  is ``True`` for backward compatibility reasons, but will change to ``False``
  in Python 3.6.  (Contributed by Maciej Szulik in :issue:`19662`.)

* It is now possible to provide, directly or via name resolution, IPv6
  addresses in the :class:`~smtpd.SMTPServer` constructor, and have it
  successfully connect.  (Contributed by Milan Oberkirch in :issue:`14758`.)

* :mod:`~smtpd.SMTPServer` now supports :rfc:`6531` via the *enable_SMTPUTF8*
  constructor argument and a user-provided
  :meth:`~smtpd.SMTPServer.process_smtputf8_message` method.

smtplib
-------

* A new :meth:`~smtplib.SMTP.auth` method provides a convenient way to
  implement custom authentication mechanisms.
  (Contributed by Milan Oberkirch in :issue:`15014`.)

sndhdr
------

* :func:`~sndhdr.what` and :func:`~sndhdr.whathdr` now return
  :func:`~collections.namedtuple`.
  (Contributed by Claudiu Popa in :issue:`18615`.)

socket
------

* New :meth:`socket.socket.sendfile` method allows to send a file over a socket
  by using high-performance :func:`os.sendfile` function on UNIX resulting in
  uploads being from 2x to 3x faster than when using plain
  :meth:`socket.socket.send`.
  (Contributed by Giampaolo Rodola' in :issue:`17552`.)

time
----

* The :func:`time.monotonic` function is now always available.  (Contributed by
  Victor Stinner in :issue:`22043`.)

time
----

* A new :class:`urllib.request.HTTPBasicPriorAuthHandler` allows HTTP Basic
  Authentication credentials to be sent unconditionally with the first HTTP
  request, rather than waiting for a HTTP 401 Unauthorized response from the
  server.
  (Contributed by Matej Cepl in :issue:`19494`.)

wsgiref
-------

* *headers* parameter of :class:`wsgiref.headers.Headers` is now optional.
  (Contributed by Pablo Torres Navarrete and SilentGhost in :issue:`5800`.)

xmlrpc
------

* :class:`xmlrpc.client.ServerProxy` is now a :term:`context manager`.
  (Contributed by Claudiu Popa in :issue:`20627`.)


Optimizations
=============

The following performance enhancements have been added:

* Construction of ``bytes(int)`` (filled by zero bytes) is faster and use less
  memory for large objects. ``calloc()`` is used instead of ``malloc()`` to
  allocate memory for these objects.

* Some operations on :class:`~ipaddress.IPv4Network` and
  :class:`~ipaddress.IPv6Network` have been massively sped up, such as
  :meth:`~ipaddress.IPv4Network.subnets`, :meth:`~ipaddress.IPv4Network.supernet`,
  :func:`~ipaddress.summarize_address_range`, :func:`~ipaddress.collapse_addresses`.
  The speed up can range from 3x to 15x.
  (:issue:`21486`, :issue:`21487`, :issue:`20826`)


Build and C API Changes
=======================

Changes to Python's build process and to the C API include:

* New ``calloc`` functions:

  * :c:func:`PyMem_RawCalloc`
  * :c:func:`PyMem_Calloc`
  * :c:func:`PyObject_Calloc`
  * :c:func:`_PyObject_GC_Calloc`


Deprecated
==========

Unsupported Operating Systems
-----------------------------

* None yet.


Deprecated Python modules, functions and methods
------------------------------------------------

* The :mod:`formatter` module has now graduated to full deprecation and is still
  slated for removal in Python 3.6.

* :mod:`smtpd` has in the past always decoded the DATA portion of email
  messages using the ``utf-8`` codec.  This can now be controlled by the new
  *decode_data* keyword to :class:`~smtpd.SMTPServer`.  The default value is
  ``True``, but this default is deprecated.  Specify the *decode_data* keyword
  with an appropriate value to avoid the deprecation warning.


Deprecated functions and types of the C API
-------------------------------------------

* None yet.


Deprecated features
-------------------

* None yet.


Removed
=======

API and Feature Removals
------------------------

The following obsolete and previously deprecated APIs and features have been
removed:

* The ``__version__`` attribute has been dropped from the email package.  The
  email code hasn't been shipped separately from the stdlib for a long time,
  and the ``__version__`` string was not updated in the last few releases.

* The internal ``Netrc`` class in the :mod:`ftplib` module was deprecated in
  3.4, and has now been removed.
  (Contributed by Matt Chaput in :issue:`6623`.)

Porting to Python 3.5
=====================

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

Changes in the Python API
-------------------------

* Before Python 3.5, a :class:`datetime.time` object was considered to be false
  if it represented midnight in UTC.  This behavior was considered obscure and
  error-prone and has been removed in Python 3.5.  See :issue:`13936` for full
  details.

* :meth:`ssl.SSLSocket.send()` now raises either :exc:`ssl.SSLWantReadError`
  or :exc:`ssl.SSLWantWriteError` on a non-blocking socket if the operation
  would block. Previously, it would return 0.  See :issue:`20951`.

* The ``__name__`` attribute of generator is now set from the function name,
  instead of being set from the code name. Use ``gen.gi_code.co_name`` to
  retrieve the code name. Generators also have a new ``__qualname__``
  attribute, the qualified name, which is now used for the representation
  of a generator (``repr(gen)``). See :issue:`21205`.

* The deprecated "strict" mode and argument of :class:`~html.parser.HTMLParser`,
  :meth:`HTMLParser.error`, and the :exc:`HTMLParserError` exception have been
  removed.  (Contributed by Ezio Melotti in :issue:`15114`.)
  The *convert_charrefs* argument of :class:`~html.parser.HTMLParser` is
  now ``True`` by default.  (Contributed by Berker Peksag in :issue:`21047`.)

* Although it is not formally part of the API, it is worth noting for porting
  purposes (ie: fixing tests) that error messages that were previously of the
  form "'sometype' does not support the buffer protocol" are now of the form "a
  bytes-like object is required, not 'sometype'".  (Contributed by Ezio Melotti
  in :issue:`16518`.)

* If the current directory is set to a directory that no longer exists then
  :exc:`FileNotFoundError` will no longer be raised and instead
  :meth:`~importlib.machinery.FileFinder.find_spec` will return ``None``
  **without** caching ``None`` in :data:`sys.path_importer_cache` which is
  different than the typical case (:issue:`22834`).

* HTTP status code and messages from `http.client` and `http.server` were
  refactored into a common :class:`~http.HTTPStatus` enum.  The values in
  `http.client` and `http.server` remain available for backwards compatibility.
  (Contributed by Demian Brecht in :issue:`21793`.)

* When an import loader defines :meth:`~importlib.machinery.Loader.exec_module`
  it is now expected to also define
  :meth:`~importlib.machinery.Loader.create_module` (raises a
  :exc:`DeprecationWarning` now, will be an error in Python 3.6). If the loader
  inherits from :class:`importlib.abc.Loader` then there is nothing to do, else
  simply define :meth:`~importlib.machinery.Loader.create_module` to return
  ``None`` (:issue:`23014`).

Changes in the C API
--------------------

* The :c:type:`PyMemAllocator` structure was renamed to
  :c:type:`PyMemAllocatorEx` and a new ``calloc`` field was added.

* Removed non-documented macro :c:macro:`PyObject_REPR` which leaked references.
  Use format character ``%R`` in :c:func:`PyUnicode_FromFormat`-like functions
  to format the :func:`repr` of the object.