cpython/Doc/whatsnew/3.5.rst

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****************************
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`).
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`).
os
--
* :class:`os.stat_result` now has a ``st_file_attributes`` field on Windows,
containing the ``dwFileAttributes`` member of the
``BY_HANDLE_FILE_INFORMATION`` structure returned by
``GetFileInformationByHandle()`` (contributed by Ben Hoyt in
:issue:`21719`).
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`.)
smtplib
-------
* A new :meth:`~smtplib.SMTP.auth` method provides a convenient way to
implement custom authentication mechanisms (contributed by Milan Oberkirch in
:issue:`15014`).
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`)
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.
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`.
Changes in the C API
--------------------
* The :c:type:`PyMemAllocator` structure was renamed to
:c:type:`PyMemAllocatorEx` and a new ``calloc`` field was added.