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:`478` - Python 3.5 Release Schedule
Summary -- Release highlights
=============================
.. This section singles out the most important changes in Python 3.5.
Brevity is key.
New syntax features:
* :pep:`465`, a new matrix multiplication operator: ``a @ b``.
New library modules:
* :mod:`zipapp`: :ref:`Improving Python ZIP Application Support
<whatsnew-zipapp>` (:pep:`441`).
New built-in features:
* ``bytes % args``, ``bytearray % args``: :pep:`461` - Adding ``%`` formatting
to bytes and bytearray
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
PEP 461 - Adding % formatting to bytes and bytearray
----------------------------------------------------
This PEP proposes adding % formatting operations similar to Python 2's ``str``
type to :class:`bytes` and :class:`bytearray`.
Examples::
>>> b'Hello %s!' % b'World'
b'Hello World!'
>>> b'x=%i y=%f' % (1, 2.5)
b'x=1 y=2.500000'
Unicode is not allowed for ``%s``, but it is accepted by ``%a`` (equivalent of
``repr(obj).encode('ascii', 'backslashreplace')``)::
>>> b'Hello %s!' % 'World'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'
>>> b'price: %a' % '10€'
b"price: '10\\u20ac'"
.. seealso::
:pep:`461` -- Adding % formatting to bytes and bytearray
PEP 465 - A dedicated infix operator for matrix multiplication
--------------------------------------------------------------
This PEP proposes a new binary operator to be used for matrix multiplication,
called ``@``. (Mnemonic: ``@`` is ``*`` for mATrices.)
.. seealso::
:pep:`465` -- A dedicated infix operator for matrix multiplication
PEP 471 - os.scandir() function -- a better and faster directory iterator
-------------------------------------------------------------------------
:pep:`471` adds a new directory iteration function, :func:`os.scandir`,
to the standard library. Additionally, :func:`os.walk` is now
implemented using :func:`os.scandir`, which speeds it up by 3-5 times
on POSIX systems and by 7-20 times on Windows systems.
PEP and implementation written by Ben Hoyt with the help of Victor Stinner.
.. seealso::
:pep:`471` -- os.scandir() function -- a better and faster directory
iterator
PEP 475: Retry system calls failing with EINTR
----------------------------------------------
:pep:`475` adds support for automatic retry of system calls failing with
:py:data:`~errno.EINTR`: this means that user code doesn't have to deal with
EINTR or :exc:`InterruptedError` manually, and should make it more robust
against asynchronous signal reception.
.. seealso::
:pep:`475` -- Retry system calls failing with EINTR
PEP 486: Make the Python Launcher aware of virtual environments
---------------------------------------------------------------
:pep:`486` makes the Windows launcher (see :pep:`397`) aware of an active
virtual environment. When the default interpreter would be used and the
``VIRTUAL_ENV`` environment variable is set, the interpreter in the virtual
environment will be used.
.. seealso::
:pep:`486` -- Make the Python Launcher aware of virtual environments
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`.)
* The :option:`-b` option now affects comparisons of :class:`bytes` with
:class:`int`. (Contributed by Serhiy Storchaka in :issue:`23681`)
New Modules
===========
.. _whatsnew-zipapp:
zipapp
------
The new :mod:`zipapp` module (specified in :pep:`441`) provides an API and
command line tool for creating executable Python Zip Applications, which
were introduced in Python 2.6 in :issue:`1739468` but which were not well
publicised, either at the time or since.
With the new module, bundling your application is as simple as putting all
the files, including a ``__main__.py`` file, into a directory ``myapp``
and running::
$ python -m zipapp myapp
$ python myapp.pyz
Improved Modules
================
argparse
--------
* :class:`~argparse.ArgumentParser` now allows to disable
:ref:`abbreviated usage <prefix-matching>` of long options by setting
:ref:`allow_abbrev` to ``False``.
(Contributed by Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson.)
cgi
---
* :class:`~cgi.FieldStorage` now supports the context management protocol.
(Contributed by Berker Peksag in :issue:`20289`.)
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`.)
difflib
-------
* The charset of the HTML document generated by :meth:`difflib.HtmlDiff.make_file`
can now be customized by using *charset* keyword-only parameter. The default
charset of HTML document changed from ``'ISO-8859-1'`` to ``'utf-8'``.
(Contributed by Berker Peksag in :issue:`2052`.)
distutils
---------
* The ``build`` and ``build_ext`` commands now accept a ``-j``
option to enable parallel building of extension modules.
(Contributed by Antoine Pitrou in :issue:`5309`.)
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 Claudiu 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
--
* New :func:`os.scandir` function that exposes file information from
the operating system when listing a directory. :func:`os.scandir`
returns an iterator of :class:`os.DirEntry` objects corresponding to
the entries in the directory given by *path*. (Contributed by Ben
Hoyt with the help of Victor Stinner in :issue:`22524`.)
* :class:`os.stat_result` now has a :attr:`~os.stat_result.st_file_attributes`
attribute on Windows. (Contributed by Ben Hoyt in :issue:`21719`.)
os.path
-------
* New :func:`~os.path.commonpath` function that extracts common path prefix.
Unlike the :func:`~os.path.commonprefix` function, it always returns a valid
patch. (Contributed by Rafik Draoui and Serhiy Storchaka in :issue:`10395`.)
pickle
------
* Serializing more "lookupable" objects (such as unbound methods or nested
classes) now are supported with pickle protocols < 4.
(Contributed by Serhiy Storchaka in :issue:`23611`.)
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
------
* On Windows, :func:`signal.set_wakeup_fd` now also supports socket handles.
(Contributed by Victor Stinner in :issue:`22018`.)
* 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`.)
sysconfig
---------
* The user scripts directory on Windows is now versioned.
(Contributed by Paul Moore in :issue:`23437`.)
tarfile
-------
* The :func:`tarfile.open` function now supports ``'x'`` (exclusive creation)
mode. (Contributed by Berker Peksag in :issue:`21717`.)
time
----
* The :func:`time.monotonic` function is now always available. (Contributed by
Victor Stinner in :issue:`22043`.)
urllib
------
* 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`.)
faulthandler
------------
* :func:`~faulthandler.enable`, :func:`~faulthandler.register`,
:func:`~faulthandler.dump_traceback` and
:func:`~faulthandler.dump_traceback_later` functions now accept file
descriptors. (Contributed by Wei Wu in :issue:`23566`.)
zipfile
-------
* Added support for writing ZIP files to unseekable streams.
(Contributed by Serhiy Storchaka in :issue:`23252`.)
* The :func:`zipfile.ZipFile.open` function now supports ``'x'`` (exclusive
creation) mode. (Contributed by Serhiy Storchaka in :issue:`21717`.)
Optimizations
=============
The following performance enhancements have been added:
* :func:`os.walk` has been sped up by 3-5x on POSIX systems and 7-20x
on Windows. This was done using the new :func:`os.scandir` function,
which exposes file information from the underlying ``readdir`` and
``FindFirstFile``/``FindNextFile`` system calls. (Contributed by
Ben Hoyt with help from Victor Stinner in :issue:`23605`.)
* 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`)
* Many operations on :class:`io.BytesIO` are now 50% to 100% faster.
(Contributed by Serhiy Storchaka in :issue:`15381` and David Wilson in
:issue:`22003`.)
* :func:`marshal.dumps` is now faster (65%-85% with versions 3--4, 20-25% with
versions 0--2 on typical data, and up to 5x in best cases).
(Contributed by Serhiy Storchaka in :issue:`20416` and :issue:`23344`.)
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.
* Directly assigning values to the :attr:`~http.cookies.Morsel.key`,
:attr:`~http.cookies.Morsel.value` and
:attr:`~http.cookies.Morsel.coded_value` of :class:`~http.cookies.Morsel`
objects is deprecated. Use the :func:`~http.cookies.Morsel.set` method
instead. In addition, the undocumented *LegalChars* parameter of
:func:`~http.cookies.Morsel.set` is deprecated, and is now ignored.
* Passing a format string as keyword argument *format_string* to the
:meth:`~string.Formatter.format` method of the :class:`string.Formatter`
class has been deprecated.
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
-------------------------
* :pep:`475`: Examples of functions which are now retried when interrupted
instead of raising :exc:`InterruptedError` if the signal handler does not
raise an exception:
- :func:`open`, :func:`os.open`, :func:`io.open`
- :func:`os.read`, :func:`os.write`
- :func:`select.select`, :func:`select.poll.poll`, :func:`select.epoll.poll`,
:func:`select.kqueue.control`, :func:`select.devpoll.poll`
- :func:`signal.sigtimedwait`, :func:`signal.sigwaitinfo`
- :func:`time.sleep`
* 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 :mod:`http.client` and :mod:`http.server`
were refactored into a common :class:`~http.HTTPStatus` enum. The values in
:mod:`http.client` and :mod:`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`).
* :func:`re.split` always ignored empty pattern matches, so the ``'x*'``
pattern worked the same as ``'x+'``, and the ``'\b'`` pattern never worked.
Now :func:`re.split` raises a warning if the pattern could match
an empty string. For compatibility use patterns that never match an empty
string (e.g. ``'x+'`` instead of ``'x*'``). Patterns that could only match
an empty string (such as ``'\b'``) now raise an error.
* The :class:`~http.cookies.Morsel` dict-like interface has been made self
consistent: morsel comparison now takes the :attr:`~http.cookies.Morsel.key`
and :attr:`~http.cookies.Morsel.value` into account,
:meth:`~http.cookies.Morsel.copy` now results in a
:class:`~http.cookies.Morsel` instance rather than a :class:`dict`, and
:meth:`~http.cookies.Morsel.update` will now raise an exception if any of the
keys in the update dictionary are invalid. In addition, the undocumented
*LegalChars* parameter of :func:`~http.cookies.Morsel.set` is deprecated and
is now ignored. (:issue:`2211`)
Changes in the C API
--------------------
* The undocumented :c:member:`~PyMemoryViewObject.format` member of the
(non-public) :c:type:`PyMemoryViewObject` structure has been removed.
All extensions relying on the relevant parts in ``memoryobject.h``
must be rebuilt.
* 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.
* Because the lack of the :attr:`__module__` attribute breaks pickling and
introspection, a deprecation warning now is raised for builtin type without
the :attr:`__module__` attribute. Would be an AttributeError in future.
(:issue:`20204`)