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ReStructuredText
929 lines
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ReStructuredText
****************************
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What's New In Python 3.4
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****************************
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.. :Author: Someone <email>
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(uncomment if there is a principal author)
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.. Rules for maintenance:
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* Anyone can add text to this document, but the maintainer reserves the
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right to rewrite any additions. In particular, for obscure or esoteric
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features, the maintainer may reduce any addition to a simple reference to
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the new documentation rather than explaining the feature inline.
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* While the maintainer will periodically go through Misc/NEWS
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and add changes, it's best not to rely on this. We know from experience
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that any changes that aren't in the What's New documentation around the
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time of the original release will remain largely unknown to the community
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for years, even if they're added later. We also know from experience that
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other priorities can arise, and the maintainer will run out of time to do
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updates - in such cases, end users will be much better served by partial
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notifications that at least give a hint about new features to
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investigate.
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* This is not a complete list of every single change; completeness
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is the purpose of Misc/NEWS. The What's New should focus on changes that
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are visible to Python *users* and that *require* a feature release (i.e.
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most bug fixes should only be recorded in Misc/NEWS)
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* PEPs should not be marked Final until they have an entry in What's New.
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A placeholder entry that is just a section header and a link to the PEP
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(e.g ":pep:`397` has been implemented") is acceptable. If a PEP has been
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implemented and noted in What's New, don't forget to mark it as Final!
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* If you want to draw your new text to the attention of the
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maintainer, add 'XXX' to the beginning of the paragraph or
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section.
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* It's OK to add just a very brief note about a change. For
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example: "The :ref:`~socket.transmogrify()` function was added to the
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:mod:`socket` module." The maintainer will research the change and
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write the necessary text (if appropriate). The advantage of doing this
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is that even if no more descriptive text is ever added, readers will at
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least have a notification that the new feature exists and a link to the
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relevant documentation.
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* You can comment out your additions if you like, but it's not
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necessary (especially when a final release is some months away).
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* Credit the author of a patch or bugfix. Just the name is
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sufficient; the e-mail address isn't necessary.
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* It's helpful to add the bug/patch number as a comment:
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The :ref:`~socket.transmogrify()` function was added to the
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:mod:`socket` module. (Contributed by P.Y. Developer in :issue:`12345`.)
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This saves the maintainer the effort of going through the Mercurial log
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when researching a change.
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* Cross referencing tip: :ref:`mod.attr` will display as ``mod.attr``,
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while :ref:`~mod.attr` will display as ``attr``.
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This article explains the new features in Python 3.4, compared to 3.3.
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.. Python 3.4 was released on TBD.
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For full details, see the
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`changelog <http://docs.python.org/3.4/whatsnew/changelog.html>`_.
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.. note:: Prerelease users should be aware that this document is currently in
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draft form. It will be updated substantially as Python 3.4 moves towards
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release, so it's worth checking back even after reading earlier versions.
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.. seealso::
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:pep:`429` - Python 3.4 Release Schedule
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Summary -- Release highlights
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=============================
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.. This section singles out the most important changes in Python 3.4.
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Brevity is key.
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New syntax features:
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* No new syntax features are planned for Python 3.4.
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New library modules:
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* :mod:`asyncio`: New provisonal API for asynchronous IO (:pep:`3156`).
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* :mod:`enum`: Support for enumeration types (:pep:`435`).
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* :mod:`ensurepip`: Bootstrapping the pip installer (:pep:`453`).
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* :mod:`selectors`: High-level and efficient I/O multiplexing, built upon the
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:mod:`select` module primitives.
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* :mod:`statistics`: A basic numerically stable statistics library (:pep:`450`).
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New expected features for Python implementations:
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* :ref:`PEP 446: Make newly created file descriptors non-inheritable <pep-446>`.
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* command line option for :ref:`isolated mode <using-on-misc-options>`,
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(:issue:`16499`).
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* improvements to handling of non-Unicode codecs
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Significantly Improved Library Modules:
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* Single-dispatch generic functions in :mod:`functoools` (:pep:`443`)
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* SHA-3 (Keccak) support for :mod:`hashlib`.
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* TLSv1.1 and TLSv1.2 support for :mod:`ssl`.
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* :mod:`multiprocessing` now has option to avoid using :func:`os.fork`
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on Unix (:issue:`8713`).
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CPython implementation improvements:
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* :ref:`PEP 442: Safe object finalization <pep-442>`
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* :ref:`PEP 445: Configurable memory allocators <pep-445>`
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* Improve finalization of Python modules to avoid setting their globals
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to None, in most cases (:issue:`18214`).
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* A more efficient :mod:`marshal` format (:issue:`16475`).
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* "Argument Clinic", an initial step towards providing improved introspection
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support for builtin and standard library extension types implemented in C
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(:pep:`436`)
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Please read on for a comprehensive list of user-facing changes.
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PEP 453: Explicit bootstrapping of pip in Python installations
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==============================================================
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The new :mod:`ensurepip` module (defined in :pep:`453`) provides a standard
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cross-platform mechanism to boostrap the pip installer into Python
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installations and virtual environments.
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.. note::
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Only the first phase of PEP 453 has been implemented at this point.
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This section will be fleshed out with additional details once those
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other changes are implemented.
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Refer to :issue:`19347` for the progress on additional steps:
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* ``make install`` and ``make altinstall`` integration
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* Windows installer integration
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* Mac OS X installer integration
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* :mod:`venv` module and :command:`pyvenv` integration
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.. seealso::
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:pep:`453` - Explicit bootstrapping of pip in Python installations
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PEP written by Donald Stufft and Nick Coghlan, implemented by
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Donald Stufft, Nick Coghlan (and ...).
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.. _pep-446:
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PEP 446: Make newly created file descriptors non-inheritable
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============================================================
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:pep:`446` makes newly created file descriptors :ref:`non-inheritable
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<fd_inheritance>`. New functions and methods:
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* :func:`os.get_inheritable`, :func:`os.set_inheritable`
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* :func:`os.get_handle_inheritable`, :func:`os.set_handle_inheritable`
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* :meth:`socket.socket.get_inheritable`, :meth:`socket.socket.set_inheritable`
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.. seealso::
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:pep:`446` - Make newly created file descriptors non-inheritable
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PEP written and implemented by Victor Stinner.
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Improvements to handling of non-Unicode codecs
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==============================================
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Since it was first introduced, the :mod:`codecs` module has always been
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intended to operate as a type-neutral dynamic encoding and decoding
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system. However, its close coupling with the Python text model, especially
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the type restricted convenience methods on the builtin :class:`str`,
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:class:`bytes` and :class:`bytearray` types, has historically obscured that
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fact.
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As a key step in clarifying the situation, the :meth:`codecs.encode` and
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:meth:`codecs.decode` convenience functions are now properly documented in
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Python 2.7, 3.3 and 3.4. These functions have existed in the :mod:`codecs`
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module and have been covered by the regression test suite since Python 2.4,
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but were previously only discoverable through runtime introspection.
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Unlike the convenience methods on :class:`str`, :class:`bytes` and
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:class:`bytearray`, these convenience functions support arbitrary codecs
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in both Python 2 and Python 3, rather than being limited to Unicode text
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encodings (in Python 3) or ``basestring`` <-> ``basestring`` conversions
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(in Python 2).
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In Python 3.4, the errors raised by the convenience methods when a codec
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produces the incorrect output type have also been updated to direct users
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towards these general purpose convenience functions::
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>>> import codecs
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>>> codecs.encode(b"hello", "bz2_codec").decode("bz2_codec")
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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TypeError: 'bz2_codec' decoder returned 'bytes' instead of 'str'; use codecs.decode() to decode to arbitrary types
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>>> "hello".encode("rot_13")
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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TypeError: 'rot_13' encoder returned 'str' instead of 'bytes'; use codecs.encode() to encode to arbitrary types
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In a related change, whenever it is feasible without breaking backwards
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compatibility, exceptions raised during encoding and decoding operations
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will be wrapped in a chained exception of the same type that mentions the
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name of the codec responsible for producing the error::
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>>> b"hello".decode("uu_codec")
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ValueError: Missing "begin" line in input data
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The above exception was the direct cause of the following exception:
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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ValueError: decoding with 'uu_codec' codec failed (ValueError: Missing "begin" line in input data)
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>>> "hello".encode("bz2_codec")
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TypeError: 'str' does not support the buffer interface
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The above exception was the direct cause of the following exception:
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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TypeError: encoding with 'bz2_codec' codec failed (TypeError: 'str' does not support the buffer interface)
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(Contributed by Nick Coghlan in :issue:`17827` and :issue:`17828`)
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Other Language Changes
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======================
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Some smaller changes made to the core Python language are:
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* Unicode database updated to UCD version 6.3.
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* :func:`min` and :func:`max` now accept a *default* argument that can be used
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to specify the value they return if the iterable they are evaluating has no
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elements. Contributed by Julian Berman in :issue:`18111`.
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* Module objects are now :mod:`weakref`'able.
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* Module ``__file__`` attributes (and related values) should now always
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contain absolute paths by default, with the sole exception of
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``__main__.__file__`` when a script has been executed directly using
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a relative path (Contributed by Brett Cannon in :issue:`18416`).
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* Now all the UTF-\* codecs (except UTF-7) reject surrogates during both
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encoding and decoding unless the ``surrogatepass`` error handler is used,
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with the exception of the UTF-16 decoder that accepts valid surrogate pairs,
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and the UTF-16 encoder that produces them while encoding non-BMP characters.
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Contributed by Victor Stinner, Kang-Hao (Kenny) Lu and Serhiy Storchaka in
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:issue:`12892`.
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New Modules
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===========
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asyncio
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-------
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The new :mod:`asyncio` module (defined in :pep:`3156`) provides a standard
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pluggable event loop model for Python, providing solid asynchronous IO
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support in the standard library, and making it easier for other event loop
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implementations to interoperate with the standard library and each other.
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For Python 3.4, this module is considered a :term:`provisional API`.
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.. seealso::
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:pep:`3156` - Asynchronous IO Support Rebooted: the "asyncio" Module
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PEP written and implementation led by Guido van Rossum.
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enum
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----
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The new :mod:`enum` module (defined in :pep:`435`) provides a standard
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implementation of enumeration types, allowing other modules (such as
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:mod:`socket`) to provide more informative error messages and better
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debugging support by replacing opaque integer constants with backwards
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compatible enumeration values.
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.. seealso::
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:pep:`435` - Adding an Enum type to the Python standard library
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PEP written by Barry Warsaw, Eli Bendersky and Ethan Furman,
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implemented by Ethan Furman.
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selectors
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---------
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The new :mod:`selectors` module (created as part of implementing :pep:`3156`)
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allows high-level and efficient I/O multiplexing, built upon the
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:mod:`select` module primitives.
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statistics
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----------
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The new :mod:`statistics` module (defined in :pep:`450`) offers some core
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statistics functionality directly in the standard library. This module
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supports calculation of the mean, median, mode, variance and standard
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deviation of a data series.
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.. seealso::
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:pep:`450` - Adding A Statistics Module To The Standard Library
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PEP written and implemented by Steven D'Aprano
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Improved Modules
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================
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aifc
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----
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The :meth:`~aifc.getparams` method now returns a namedtuple rather than a
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plain tuple. (Contributed by Claudiu Popa in :issue:`17818`.)
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audioop
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-------
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Added support for 24-bit samples (:issue:`12866`).
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base64
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------
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The encoding and decoding functions in :mod:`base64` now accept any
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:term:`bytes-like object` in cases where it previously required a
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:class:`bytes` or :class:`bytearray` instance (:issue`17839`)
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colorsys
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--------
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The number of digits in the coefficients for the RGB --- YIQ conversions have
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been expanded so that they match the FCC NTSC versions. The change in
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results should be less than 1% and may better match results found elsewhere.
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contextlib
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----------
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The new :class:`contextlib.suppress` context manager helps to clarify the
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intent of code that deliberately suppresses exceptions from a single
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statement. (Contributed by Raymond Hettinger in :issue:`15806` and
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Zero Piraeus in :issue:`19266`)
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The new :func:`contextlib.redirect_stdout` context manager makes it easier
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for utility scripts to handle inflexible APIs that don't provide any
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options to retrieve their output as a string or direct it to somewhere
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other than :data:`sys.stdout`. In conjunction with :class:`io.StringIO`,
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this context manager is also useful for checking expected output from
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command line utilities. (Contribute by Raymond Hettinger in :issue:`15805`)
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The :mod:`contextlib` documentation has also been updated to include a
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:ref:`discussion <single-use-reusable-and-reentrant-cms>` of the
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differences between single use, reusable and reentrant context managers.
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dis
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---
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The :mod:`dis` module is now built around an :class:`~dis.Instruction` class
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that provides details of individual bytecode operations and a
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:func:`~dis.get_instructions` iterator that emits the Instruction stream for a
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given piece of Python code. The various display tools in the :mod:`dis`
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module have been updated to be based on these new components.
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The new :class:`dis.Bytecode` class provides an object-oriented API for
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inspecting bytecode, both in human-readable form and for iterating over
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instructions.
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(Contributed by Nick Coghlan, Ryan Kelly and Thomas Kluyver in :issue:`11816`)
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doctest
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-------
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Added :data:`~doctest.FAIL_FAST` flag to halt test running as soon as the first
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failure is detected. (Contributed by R. David Murray and Daniel Urban in
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:issue:`16522`.)
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Updated the doctest command line interface to use :mod:`argparse`, and added
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``-o`` and ``-f`` options to the interface. ``-o`` allows doctest options to
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be specified on the command line, and ``-f`` is a shorthand for ``-o
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FAIL_FAST`` (to parallel the similar option supported by the :mod:`unittest`
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CLI). (Contributed by R. David Murray in :issue:`11390`.)
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email
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-----
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:meth:`~email.message.Message.as_string` now accepts a *policy* argument to
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override the default policy of the message when generating a string
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representation of it. This means that ``as_string`` can now be used in more
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circumstances, instead of having to create and use a :mod:`~email.generator` in
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order to pass formatting parameters to its ``flatten`` method.
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New method :meth:`~email.message.Message.as_bytes` added to produce a bytes
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representation of the message in a fashion similar to how ``as_string``
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produces a string representation. It does not accept the *maxheaderlen*
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argument, but does accept the *unixfrom* and *policy* arguments. The
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:class:`~email.message.Message` :meth:`~email.message.Message.__bytes__` method
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calls it, meaning that ``bytes(mymsg)`` will now produce the intuitive
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result: a bytes object containing the fully formatted message.
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(Contributed by R. David Murray in :issue:`18600`.)
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A pair of new subclasses of :class:`~email.message.Message` have been added,
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along with a new sub-module, :mod:`~email.contentmanager`. All documentation
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is currently in the new module, which is being added as part of the new
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:term:`provisional <provisional package>` email API. These classes provide a
|
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number of new methods that make extracting content from and inserting content
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into email messages much easier. See the :mod:`~email.contentmanager`
|
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documentation for details.
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These API additions complete the bulk of the work that was planned as part of
|
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the email6 project. The currently provisional API is scheduled to become final
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in Python 3.5 (possibly with a few minor additions in the area of error
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handling).
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(Contributed by R. David Murray in :issue:`18891`.)
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functools
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---------
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The new :func:`~functools.partialmethod` descriptor bring partial argument
|
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application to descriptors, just as :func:`~functools.partial` provides
|
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for normal callables. The new descriptor also makes it easier to get
|
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arbitrary callables (including :func:`~functools.partial` instances)
|
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to behave like normal instance methods when included in a class definition.
|
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|
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(Contributed by Alon Horev and Nick Coghlan in :issue:`4331`)
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|
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The new :func:`~functools.singledispatch` decorator brings support for
|
|
single-dispatch generic functions to the Python standard library. Where
|
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object oriented programming focuses on grouping multiple operations on a
|
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common set of data into a class, a generic function focuses on grouping
|
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multiple implementations of an operation that allows it to work with
|
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*different* kinds of data.
|
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|
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.. seealso::
|
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|
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:pep:`443` - Single-dispatch generic functions
|
|
PEP written and implemented by Łukasz Langa.
|
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|
|
|
|
hashlib
|
|
-------
|
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|
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New :func:`hashlib.pbkdf2_hmac` function.
|
|
|
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(Contributed by Christian Heimes in :issue:`18582`)
|
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|
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inspect
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-------
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The inspect module now offers a basic :ref:`command line interface
|
|
<inspect-module-cli>` to quickly display source code and other
|
|
information for modules, classes and functions. (Contributed by Claudiu Popa
|
|
and Nick Coghlan in :issue:`18626`)
|
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|
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:func:`~inspect.unwrap` makes it easy to unravel wrapper function chains
|
|
created by :func:`functools.wraps` (and any other API that sets the
|
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``__wrapped__`` attribute on a wrapper function). (Contributed by
|
|
Daniel Urban, Aaron Iles and Nick Coghlan in :issue:`13266`)
|
|
|
|
As part of the implementation of the new :mod:`enum` module, the
|
|
:mod:`inspect` module now has substantially better support for custom
|
|
``__dir__`` methods and dynamic class attributes provided through
|
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metaclasses (Contributed by Ethan Furman in :issue:`18929` and
|
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:issue:`19030`)
|
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|
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|
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mmap
|
|
----
|
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mmap objects can now be weakref'ed.
|
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|
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(Contributed by Valerie Lambert in :issue:`4885`.)
|
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|
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|
|
multiprocessing
|
|
---------------
|
|
|
|
On Unix two new *start methods* have been added for starting processes
|
|
using :mod:`multiprocessing`. These make the mixing of processes with
|
|
threads more robust. See :issue:`8713`.
|
|
|
|
Also, except when using the old *fork* start method, child processes
|
|
will no longer inherit unneeded handles/file descriptors from their parents.
|
|
|
|
|
|
os
|
|
--
|
|
|
|
New functions to get and set the :ref:`inheritable flag <fd_inheritance>` of a file
|
|
descriptors or a Windows handle:
|
|
|
|
* :func:`os.get_inheritable`, :func:`os.set_inheritable`
|
|
* :func:`os.get_handle_inheritable`, :func:`os.set_handle_inheritable`
|
|
|
|
|
|
pdb
|
|
---
|
|
|
|
The ``print`` command has been removed from :mod:`pdb`, restoring access to the
|
|
``print`` function.
|
|
|
|
Rationale: Python2's ``pdb`` did not have a ``print`` command; instead,
|
|
entering ``print`` executed the ``print`` statement. In Python3 ``print`` was
|
|
mistakenly made an alias for the pdb :pdbcmd:`p` command. ``p``, however,
|
|
prints the ``repr`` of its argument, not the ``str`` like the Python2 ``print``
|
|
command did. Worse, the Python3 ``pdb print`` command shadowed the Python3
|
|
``print`` function, making it inaccessible at the ``pdb`` prompt.
|
|
|
|
(Contributed by Connor Osborn in :issue:`18764`.)
|
|
|
|
|
|
poplib
|
|
------
|
|
|
|
New :meth:`~poplib.POP3.stls` method to switch a clear-text POP3 session into
|
|
an encrypted POP3 session.
|
|
|
|
New :meth:`~poplib.POP3.capa` method to query the capabilities advertised by the
|
|
POP3 server.
|
|
|
|
(Contributed by Lorenzo Catucci in :issue:`4473`.)
|
|
|
|
|
|
pprint
|
|
------
|
|
|
|
The :mod:`pprint` module now supports *compact* mode for formatting long
|
|
sequences (:issue:`19132`).
|
|
|
|
|
|
pydoc
|
|
-----
|
|
|
|
While significant changes have not been made to :mod:`pydoc` directly,
|
|
its handling of custom ``__dir__`` methods and various descriptor
|
|
behaviours has been improved substantially by the underlying changes in
|
|
the :mod:`inspect` module.
|
|
|
|
|
|
resource
|
|
--------
|
|
|
|
New :func:`resource.prlimit` function and Linux specific constants.
|
|
(Contributed by Christian Heimes in :issue:`16595` and :issue:`19324`.)
|
|
|
|
smtplib
|
|
-------
|
|
|
|
:exc:`~smtplib.SMTPException` is now a subclass of :exc:`OSError`, which allows
|
|
both socket level errors and SMTP protocol level errors to be caught in one
|
|
try/except statement by code that only cares whether or not an error occurred.
|
|
(:issue:`2118`).
|
|
|
|
|
|
socket
|
|
------
|
|
|
|
Socket objects have new methods to get or set their :ref:`inheritable flag
|
|
<fd_inheritance>`:
|
|
|
|
* :meth:`socket.socket.get_inheritable`, :meth:`socket.socket.set_inheritable`
|
|
|
|
The ``socket.AF_*`` and ``socket.SOCK_*`` constants are enumeration values,
|
|
using the new :mod:`enum` module. This allows descriptive reporting during
|
|
debugging, instead of seeing integer "magic numbers".
|
|
|
|
ssl
|
|
---
|
|
|
|
TLSv1.1 and TLSv1.2 support.
|
|
|
|
(Contributed by Michele Orrù and Antoine Pitrou in :issue:`16692`)
|
|
|
|
* New diagnostic functions :func:`~ssl.get_default_verify_paths`,
|
|
:meth:`~ssl.SSLContext.cert_store_stats` and
|
|
:meth:`~ssl.SSLContext.get_ca_certs`
|
|
|
|
* Add :func:`ssl.enum_cert_store` to retrieve certificates and CRL from Windows'
|
|
cert store.
|
|
|
|
(Contributed by Christian Heimes in :issue:`18143`, :issue:`18147` and
|
|
:issue:`17134`.)
|
|
|
|
Support for server-side SNI using the new
|
|
:meth:`ssl.SSLContext.set_servername_callback` method.
|
|
|
|
(Contributed by Daniel Black in :issue:`8109`.)
|
|
|
|
|
|
stat
|
|
----
|
|
|
|
The :mod:`stat` module is now backed by a C implementation in :mod:`_stat`. A C
|
|
implementation is required as most of the values aren't standardized and
|
|
platform-dependent. (Contributed by Christian Heimes in :issue:`11016`.)
|
|
|
|
The module supports new file types: door, event port and whiteout.
|
|
|
|
|
|
struct
|
|
------
|
|
|
|
Streaming struct unpacking using :func:`struct.iter_unpack`.
|
|
|
|
(Contributed by Antoine Pitrou in :issue:`17804`.)
|
|
|
|
|
|
sunau
|
|
-----
|
|
|
|
The :meth:`~sunau.getparams` method now returns a namedtuple rather than a
|
|
plain tuple. (Contributed by Claudiu Popa in :issue:`18901`.)
|
|
|
|
:meth:`sunau.open` now supports the context manager protocol (:issue:`18878`).
|
|
|
|
|
|
traceback
|
|
---------
|
|
|
|
A new :func:`traceback.clear_frames` function takes a traceback object
|
|
and clears the local variables in all of the frames it references,
|
|
reducing the amount of memory consumed (:issue:`1565525`).
|
|
|
|
|
|
urllib
|
|
------
|
|
|
|
Add support.for ``data:`` URLs in :mod:`urllib.request`.
|
|
|
|
(Contributed by Mathias Panzenböck in :issue:`16423`.)
|
|
|
|
|
|
unittest
|
|
--------
|
|
|
|
Support for easy dynamically-generated subtests using the
|
|
:meth:`~unittest.TestCase.subTest` context manager.
|
|
|
|
(Contributed by Antoine Pitrou in :issue:`16997`.)
|
|
|
|
|
|
wave
|
|
----
|
|
|
|
The :meth:`~wave.getparams` method now returns a namedtuple rather than a
|
|
plain tuple. (Contributed by Claudiu Popa in :issue:`17487`.)
|
|
|
|
:meth:`wave.open` now supports the context manager protocol. (Contributed
|
|
by Claudiu Popa in :issue:`17616`.)
|
|
|
|
|
|
weakref
|
|
-------
|
|
|
|
New :class:`~weakref.WeakMethod` class simulates weak references to bound
|
|
methods. (Contributed by Antoine Pitrou in :issue:`14631`.)
|
|
|
|
New :class:`~weakref.finalize` class makes it possible to register a callback
|
|
to be invoked when an object is garbage collected, without needing to
|
|
carefully manage the lifecycle of the weak reference itself. (Contributed by
|
|
Richard Oudkerk in :issue:`15528`)
|
|
|
|
|
|
xml.etree
|
|
---------
|
|
|
|
Add an event-driven parser for non-blocking applications,
|
|
:class:`~xml.etree.ElementTree.XMLPullParser`.
|
|
|
|
(Contributed by Antoine Pitrou in :issue:`17741`.)
|
|
|
|
|
|
zipfile.PyZipfile
|
|
-----------------
|
|
|
|
Add a filter function to ignore some packages (tests for instance),
|
|
:meth:`~zipfile.PyZipFile.writepy`.
|
|
|
|
(Contributed by Christian Tismer in :issue:`19274`.)
|
|
|
|
|
|
Other improvements
|
|
==================
|
|
|
|
Tab-completion is now enabled by default in the interactive interpreter.
|
|
|
|
(Contributed by Antoine Pitrou and Éric Araujo in :issue:`5845`.)
|
|
|
|
Python invocation changes
|
|
=========================
|
|
|
|
Invoking the Python interpreter with ``--version`` now outputs the version to
|
|
standard output instead of standard error (:issue:`18338`). Similar changes
|
|
were made to :mod:`argparse` (:issue:`18920`) and other modules that have
|
|
script-like invocation capabilities (:issue:`18922`).
|
|
|
|
Optimizations
|
|
=============
|
|
|
|
Major performance enhancements have been added:
|
|
|
|
* The UTF-32 decoder is now 3x to 4x faster.
|
|
|
|
* The cost of hash collisions for sets is now reduced. Each hash table
|
|
probe now checks a series of consecutive, adjacent key/hash pairs before
|
|
continuing to make random probes through the hash table. This exploits
|
|
cache locality to make collision resolution less expensive.
|
|
|
|
The collision resolution scheme can be described as a hybrid of linear
|
|
probing and open addressing. The number of additional linear probes
|
|
defaults to nine. This can be changed at compile-time by defining
|
|
LINEAR_PROBES to be any value. Set LINEAR_PROBES=0 to turn-off
|
|
linear probing entirely.
|
|
|
|
(Contributed by Raymond Hettinger in :issue:`18771`.)
|
|
|
|
* The interpreter starts about 30% faster. A couple of measures lead to the
|
|
speedup. The interpreter loads fewer modules on startup, e.g. the :mod:`re`,
|
|
:mod:`collections` and :mod:`locale` modules and their dependencies are no
|
|
longer imported by default. The marshal module has been improved to load
|
|
compiled Python code faster.
|
|
|
|
(Contributed by Antoine Pitrou, Christian Heimes and Victor Stinner in
|
|
:issue:`19219`, :issue:`19218`, :issue:`19209`, :issue:`19205` and
|
|
:issue:`9548`)
|
|
|
|
|
|
CPython Implementation Changes
|
|
==============================
|
|
|
|
|
|
.. _pep-445:
|
|
|
|
PEP 445: Customization of CPython memory allocators
|
|
---------------------------------------------------
|
|
|
|
:pep:`445` adds new C level interfaces to customize memory allocation in
|
|
the CPython interpreter.
|
|
|
|
.. seealso::
|
|
|
|
:pep:`445` - Add new APIs to customize Python memory allocators
|
|
PEP written and implemented by Victor Stinner.
|
|
|
|
|
|
.. _pep-442:
|
|
|
|
PEP 442: Safe object finalization
|
|
---------------------------------
|
|
|
|
:pep:`442` removes the current limitations and quirks of object finalization
|
|
in CPython. With it, objects with :meth:`__del__` methods, as well as
|
|
generators with :keyword:`finally` clauses, can be finalized when they are
|
|
part of a reference cycle.
|
|
|
|
As part of this change, module globals are no longer forcibly set to
|
|
:const:`None` during interpreter shutdown in most cases, instead relying
|
|
on the normal operation of the cyclic garbage collector.
|
|
|
|
.. seealso::
|
|
|
|
:pep:`442` - Safe object finalization
|
|
PEP written and implemented by Antoine Pitrou.
|
|
|
|
|
|
Other build and C API changes
|
|
-----------------------------
|
|
|
|
Changes to Python's build process and to the C API include:
|
|
|
|
* The new :c:func:`Py_SetStandardStreamEncoding` pre-initialization API
|
|
allows applications embedding the CPython interpreter to reliably force
|
|
a particular encoding and error handler for the standard streams
|
|
(Contributed by Bastien Montagne and Nick Coghlan in :issue:`16129`)
|
|
|
|
* Most Python C APIs that don't mutate string arguments are now correctly
|
|
marked as accepting ``const char *`` rather than ``char *`` (Contributed
|
|
by Serhiy Storchaka in :issue:`1772673`).
|
|
|
|
* "Argument Clinic" (:pep:`436`) is now part of the CPython build process
|
|
and can be used to simplify the process of defining and maintaining
|
|
accurate signatures for builtins and standard library extension modules
|
|
implemented in C.
|
|
|
|
.. note::
|
|
The Argument Clinic PEP is not fully up to date with the state of the
|
|
implementation. This has been deemed acceptable by the release manager
|
|
and core development team in this case, as Argument Clinic will not
|
|
be made available as a public API for third party use in Python 3.4.
|
|
|
|
|
|
Deprecated
|
|
==========
|
|
|
|
Unsupported Operating Systems
|
|
-----------------------------
|
|
|
|
* OS/2
|
|
* Windows 2000
|
|
|
|
|
|
Deprecated Python modules, functions and methods
|
|
------------------------------------------------
|
|
|
|
* :meth:`difflib.SequenceMatcher.isbjunk` and
|
|
:meth:`difflib.SequenceMatcher.isbpopular` were removed: use ``x in sm.bjunk`` and
|
|
``x in sm.bpopular``, where *sm* is a :class:`~difflib.SequenceMatcher` object.
|
|
|
|
* :func:`importlib.util.module_for_loader` is pending deprecation. Using
|
|
:func:`importlib.util.module_to_load` and
|
|
:meth:`importlib.abc.Loader.init_module_attrs` allows subclasses of a loader
|
|
to more easily customize module loading.
|
|
|
|
* The :mod:`imp` module is pending deprecation. To keep compatibility with
|
|
Python 2/3 code bases, the module's removal is currently not scheduled.
|
|
|
|
* The :mod:`formatter` module is pending deprecation and is slated for removal
|
|
in Python 3.6.
|
|
|
|
|
|
Deprecated functions and types of the C API
|
|
-------------------------------------------
|
|
|
|
* The ``PyThreadState.tick_counter`` field has been removed: its value was
|
|
meaningless since Python 3.2 ("new GIL").
|
|
|
|
|
|
Deprecated features
|
|
-------------------
|
|
|
|
* The site module adding a "site-python" directory to sys.path, if it
|
|
exists, is deprecated (:issue:`19375`).
|
|
|
|
|
|
Porting to Python 3.4
|
|
=====================
|
|
|
|
This section lists previously described changes and other bugfixes
|
|
that may require changes to your code.
|
|
|
|
* The ABCs defined in :mod:`importlib.abc` now either raise the appropriate
|
|
exception or return a default value instead of raising
|
|
:exc:`NotImplementedError` blindly. This will only affect code calling
|
|
:func:`super` and falling through all the way to the ABCs. For compatibility,
|
|
catch both :exc:`NotImplementedError` or the appropriate exception as needed.
|
|
|
|
* The module type now initializes the :attr:`__package__` and :attr:`__loader__`
|
|
attributes to ``None`` by default. To determine if these attributes were set
|
|
in a backwards-compatible fashion, use e.g.
|
|
``getattr(module, '__loader__', None) is not None``.
|
|
|
|
* :meth:`importlib.util.module_for_loader` now sets ``__loader__`` and
|
|
``__package__`` unconditionally to properly support reloading. If this is not
|
|
desired then you will need to set these attributes manually. You can use
|
|
:func:`importlib.util.module_to_load` for module management.
|
|
|
|
* Import now resets relevant attributes (e.g. ``__name__``, ``__loader__``,
|
|
``__package__``, ``__file__``, ``__cached__``) unconditionally when reloading.
|
|
|
|
* Frozen packages no longer set ``__path__`` to a list containing the package
|
|
name but an empty list instead. Determing if a module is a package should be
|
|
done using ``hasattr(module, '__path__')``.
|
|
|
|
* :c:func:`PyErr_SetImportError` now sets :exc:`TypeError` when its **msg**
|
|
argument is not set. Previously only ``NULL`` was returned with no exception
|
|
set.
|
|
|
|
* :func:`py_compile.compile` now raises :exc:`FileExistsError` if the file path
|
|
it would write to is a symlink or a non-regular file. This is to act as a
|
|
warning that import will overwrite those files with a regular file regardless
|
|
of what type of file path they were originally.
|
|
|
|
* :meth:`importlib.abc.SourceLoader.get_source` no longer raises
|
|
:exc:`ImportError` when the source code being loaded triggers a
|
|
:exc:`SyntaxError` or :exc:`UnicodeDecodeError`. As :exc:`ImportError` is
|
|
meant to be raised only when source code cannot be found but it should, it was
|
|
felt to be over-reaching/overloading of that meaning when the source code is
|
|
found but improperly structured. If you were catching ImportError before and
|
|
wish to continue to ignore syntax or decoding issues, catch all three
|
|
exceptions now.
|
|
|
|
* :func:`functools.update_wrapper` and :func:`functools.wraps` now correctly
|
|
set the ``__wrapped__`` attribute to the function being wrapper, even if
|
|
that function also had its ``__wrapped__`` attribute set. This means
|
|
``__wrapped__`` attributes now correctly link a stack of decorated
|
|
functions rather than every ``__wrapped__`` attribute in the chain
|
|
referring to the innermost function. Introspection libraries that
|
|
assumed the previous behaviour was intentional can use
|
|
:func:`inspect.unwrap` to access the first function in the chain that has
|
|
no ``__wrapped__`` attribute.
|
|
|
|
* (C API) The result of the :c:data:`PyOS_ReadlineFunctionPointer` callback must
|
|
now be a string allocated by :c:func:`PyMem_RawMalloc` or
|
|
:c:func:`PyMem_RawRealloc`, or *NULL* if an error occurred, instead of a
|
|
string allocated by :c:func:`PyMem_Malloc` or :c:func:`PyMem_Realloc`.
|
|
|
|
* :class:`importlib.machinery.PathFinder` now passes on the current working
|
|
directory to objects in :data:`sys.path_hooks` for the empty string. This
|
|
results in :data:`sys.path_importer_cache` never containing ``''``, thus
|
|
iterating through :data:`sys.path_importer_cache` based on :data:`sys.path`
|
|
will not find all keys. A module's ``__file__`` when imported in the current
|
|
working directory will also now have an absolute path, including when using
|
|
``-m`` with the interpreter (this does not influence when the path to a file
|
|
is specified on the command-line).
|