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:`4XX` - 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:

* None yet.



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

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

* None yet.


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

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`).

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`).

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”. (contribute by Giampaolo
  Rodola' in :issue:`21076`)

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)`` and ``bytearray(int)`` (filled by zero bytes)
  is faster and use less memory (until the bytearray buffer is filled with
  data) 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.


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

* None yet.


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

* None yet.


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`.

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

* The :c:type:`PyMemAllocator` structure has a new ``calloc`` field.