441 lines
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ReStructuredText
441 lines
15 KiB
ReStructuredText
****************************
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What's New In Python 3.6
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****************************
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:Release: |release|
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:Date: |today|
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.. Rules for maintenance:
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* Anyone can add text to this document. Do not spend very much time
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on the wording of your changes, because your text will probably
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get rewritten to some degree.
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* The maintainer will go through Misc/NEWS periodically and add
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changes; it's therefore more important to add your changes to
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Misc/NEWS than to this file.
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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. Some changes I consider too small
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or esoteric to include. If such a change is added to the text,
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I'll just remove it. (This is another reason you shouldn't spend
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too much time on writing your addition.)
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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 just add a fragmentary note about a change. For
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example: "XXX Describe the transmogrify() function added to the
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socket module." The maintainer will research the change and
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write the necessary text.
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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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XXX Describe the transmogrify() function added to the socket
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module.
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(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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This article explains the new features in Python 3.6, compared to 3.5.
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For full details, see the :source:`Misc/NEWS` file.
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.. note::
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Prerelease users should be aware that this document is currently in draft
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form. It will be updated substantially as Python 3.6 moves towards release,
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so it's worth checking back even after reading earlier versions.
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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 3.6.
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Brevity is key.
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* PEP 498: :ref:`Formatted string literals <whatsnew-fstrings>`
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.. PEP-sized items next.
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.. _pep-4XX:
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.. PEP 4XX: Virtual Environments
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.. =============================
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.. (Implemented by Foo Bar.)
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.. .. seealso::
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:pep:`4XX` - Python Virtual Environments
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PEP written by Carl Meyer
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New Features
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============
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.. _whatsnew-fstrings:
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PEP 498: Formatted string literals
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----------------------------------
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Formatted string literals are a new kind of string literal, prefixed
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with ``'f'``. They are similar to the format strings accepted by
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:meth:`str.format`. They contain replacement fields surrounded by
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curly braces. The replacement fields are expressions, which are
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evaluated at run time, and then formatted using the :func:`format` protocol.
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>>> name = "Fred"
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>>> f"He said his name is {name}."
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'He said his name is Fred.'
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See :pep:`498` and the main documentation at :ref:`f-strings`.
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PYTHONMALLOC environment variable
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---------------------------------
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The new :envvar:`PYTHONMALLOC` environment variable allows to set the Python
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memory allocators and/or install debug hooks.
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It is now possible to install debug hooks on Python memory allocators on Python
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compiled in release mode using ``PYTHONMALLOC=debug``. Effects of debug hooks:
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* Newly allocated memory is filled with the byte ``0xCB``
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* Freed memory is filled with the byte ``0xDB``
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* Detect violations of Python memory allocator API. For example,
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:c:func:`PyObject_Free` called on a memory block allocated by
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:c:func:`PyMem_Malloc`.
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* Detect write before the start of the buffer (buffer underflow)
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* Detect write after the end of the buffer (buffer overflow)
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* Check that the :term:`GIL <global interpreter lock>` is held when allocator
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functions of the :c:data:`PYMEM_DOMAIN_OBJ` domain (ex:
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:c:func:`PyObject_Malloc`) are called
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See the :c:func:`PyMem_SetupDebugHooks` function for debug hooks on Python
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memory allocators.
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It is now also possible to force the usage of the :c:func:`malloc` allocator of
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the C library for all Python memory allocations using ``PYTHONMALLOC=malloc``.
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It helps to use external memory debuggers like Valgrind on a Python compiled in
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release mode.
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On error, the debug hooks on Python memory allocators now use the
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:mod:`tracemalloc` module to get the traceback where a memory block was
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allocated.
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Example of fatal error on buffer overflow using
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``python3.6 -X tracemalloc=5`` (store 5 frames in traces)::
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Debug memory block at address p=0x7fbcd41666f8: API 'o'
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4 bytes originally requested
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The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
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The 8 pad bytes at tail=0x7fbcd41666fc are not all FORBIDDENBYTE (0xfb):
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at tail+0: 0x02 *** OUCH
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at tail+1: 0xfb
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at tail+2: 0xfb
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at tail+3: 0xfb
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at tail+4: 0xfb
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at tail+5: 0xfb
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at tail+6: 0xfb
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at tail+7: 0xfb
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The block was made by call #1233329 to debug malloc/realloc.
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Data at p: 1a 2b 30 00
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Memory block allocated at (most recent call first):
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File "test/test_bytes.py", line 323
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File "unittest/case.py", line 600
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File "unittest/case.py", line 648
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File "unittest/suite.py", line 122
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File "unittest/suite.py", line 84
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Fatal Python error: bad trailing pad byte
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Current thread 0x00007fbcdbd32700 (most recent call first):
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File "test/test_bytes.py", line 323 in test_hex
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File "unittest/case.py", line 600 in run
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File "unittest/case.py", line 648 in __call__
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File "unittest/suite.py", line 122 in run
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File "unittest/suite.py", line 84 in __call__
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File "unittest/suite.py", line 122 in run
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File "unittest/suite.py", line 84 in __call__
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...
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(Contributed by Victor Stinner in :issue:`26516` and :issue:`26564`.)
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Other Language Changes
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======================
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* None yet.
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New Modules
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===========
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* None yet.
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Improved Modules
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================
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datetime
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--------
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The :meth:`datetime.strftime() <datetime.datetime.strftime>` and
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:meth:`date.strftime() <datetime.date.strftime>` methods now support ISO 8601 date
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directives ``%G``, ``%u`` and ``%V``.
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(Contributed by Ashley Anderson in :issue:`12006`.)
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os
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--
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A new :meth:`~os.scandir.close` method allows explicitly closing a
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:func:`~os.scandir` iterator. The :func:`~os.scandir` iterator now
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supports the :term:`context manager` protocol. If a :func:`scandir`
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iterator is neither exhausted nor explicitly closed a :exc:`ResourceWarning`
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will be emitted in its destructor.
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(Contributed by Serhiy Storchaka in :issue:`25994`.)
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pickle
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------
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Objects that need calling ``__new__`` with keyword arguments can now be pickled
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using :ref:`pickle protocols <pickle-protocols>` older than protocol version 4.
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Protocol version 4 already supports this case. (Contributed by Serhiy
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Storchaka in :issue:`24164`.)
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rlcompleter
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-----------
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Private and special attribute names now are omitted unless the prefix starts
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with underscores. A space or a colon is added after some completed keywords.
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(Contributed by Serhiy Storchaka in :issue:`25011` and :issue:`25209`.)
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Names of most attributes listed by :func:`dir` are now completed.
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Previously, names of properties and slots which were not yet created on
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an instance were excluded. (Contributed by Martin Panter in :issue:`25590`.)
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telnetlib
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---------
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:class:`~telnetlib.Telnet` is now a context manager (contributed by
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Stéphane Wirtel in :issue:`25485`).
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unittest.mock
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-------------
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The :class:`~unittest.mock.Mock` class has the following improvements:
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* Two new methods, :meth:`Mock.assert_called()
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<unittest.mock.Mock.assert_called>` and :meth:`Mock.assert_called_once()
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<unittest.mock.Mock.assert_called_once>` to check if the mock object
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was called.
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(Contributed by Amit Saha in :issue:`26323`.)
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urllib.robotparser
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------------------
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:class:`~urllib.robotparser.RobotFileParser` now supports the ``Crawl-delay`` and
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``Request-rate`` extensions.
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(Contributed by Nikolay Bogoychev in :issue:`16099`.)
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zipfile
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-------
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A new :meth:`ZipInfo.from_file() <zipfile.ZipInfo.from_file>` class method
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allows making a :class:`~zipfile.ZipInfo` instance from a filesystem file.
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A new :meth:`ZipInfo.is_dir() <zipfile.ZipInfo.is_dir>` method can be used
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to check if the :class:`~zipfile.ZipInfo` instance represents a directory.
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(Contributed by Thomas Kluyver in :issue:`26039`.)
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zlib
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----
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The :func:`~zlib.compress` function now accepts keyword arguments.
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(Contributed by Aviv Palivoda in :issue:`26243`.)
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Optimizations
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=============
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* The ASCII decoder is now up to 60 times as fast for error handlers
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``surrogateescape``, ``ignore`` and ``replace`` (Contributed
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by Victor Stinner in :issue:`24870`).
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* The ASCII and the Latin1 encoders are now up to 3 times as fast for the
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error handler ``surrogateescape`` (Contributed by Victor Stinner in :issue:`25227`).
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* The UTF-8 encoder is now up to 75 times as fast for error handlers
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``ignore``, ``replace``, ``surrogateescape``, ``surrogatepass`` (Contributed
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by Victor Stinner in :issue:`25267`).
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* The UTF-8 decoder is now up to 15 times as fast for error handlers
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``ignore``, ``replace`` and ``surrogateescape`` (Contributed
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by Victor Stinner in :issue:`25301`).
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* ``bytes % args`` is now up to 2 times faster. (Contributed by Victor Stinner
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in :issue:`25349`).
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* ``bytearray % args`` is now between 2.5 and 5 times faster. (Contributed by
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Victor Stinner in :issue:`25399`).
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* Optimize :meth:`bytes.fromhex` and :meth:`bytearray.fromhex`: they are now
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between 2x and 3.5x faster. (Contributed by Victor Stinner in :issue:`25401`).
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Build and C API Changes
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=======================
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* New :c:func:`Py_FinalizeEx` API which indicates if flushing buffered data
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failed (:issue:`5319`).
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Deprecated
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==========
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New Keywords
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------------
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``async`` and ``await`` are not recommended to be used as variable, class,
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function or module names. Introduced by :pep:`492` in Python 3.5, they will
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become proper keywords in Python 3.7.
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Deprecated Python modules, functions and methods
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------------------------------------------------
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* :meth:`importlib.machinery.SourceFileLoader` and
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:meth:`importlib.machinery.SourcelessFileLoader` are now deprecated. They
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were the only remaining implementations of
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:meth:`importlib.abc.Loader.load_module` in :mod:`importlib` that had not
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been deprecated in previous versions of Python in favour of
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:meth:`importlib.abc.Loader.exec_module`.
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Deprecated functions and types of the C API
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-------------------------------------------
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* None yet.
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Deprecated features
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-------------------
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* The ``pyvenv`` script has been deprecated in favour of ``python3 -m venv``.
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This prevents confusion as to what Python interpreter ``pyvenv`` is
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connected to and thus what Python interpreter will be used by the virtual
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environment. (Contributed by Brett Cannon in :issue:`25154`.)
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* When performing a relative import, falling back on ``__name__`` and
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``__path__`` from the calling module when ``__spec__`` or
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``__package__`` are not defined now raises an :exc:`ImportWarning`.
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(Contributed by Rose Ames in :issue:`25791`.)
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Deprecated Python behavior
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--------------------------
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* Raising the :exc:`StopIteration` exception inside a generator will now generate a
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:exc:`DeprecationWarning`, and will trigger a :exc:`RuntimeError` in Python 3.7.
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See :ref:`whatsnew-pep-479` for details.
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Removed
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=======
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API and Feature Removals
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------------------------
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* ``inspect.getmoduleinfo()`` was removed (was deprecated since CPython 3.3).
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:func:`inspect.getmodulename` should be used for obtaining the module
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name for a given path.
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* ``traceback.Ignore`` class and ``traceback.usage``, ``traceback.modname``,
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``traceback.fullmodname``, ``traceback.find_lines_from_code``,
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``traceback.find_lines``, ``traceback.find_strings``,
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``traceback.find_executable_lines`` methods were removed from the
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:mod:`traceback` module. They were undocumented methods deprecated since
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Python 3.2 and equivalent functionality is available from private methods.
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Porting to Python 3.6
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=====================
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This section lists previously described changes and other bugfixes
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that may require changes to your code.
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Changes in the Python API
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-------------------------
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* The format of the ``co_lnotab`` attribute of code objects changed to support
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negative line number delta. By default, Python does not emit bytecode with
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negative line number delta. Functions using ``frame.f_lineno``,
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``PyFrame_GetLineNumber()`` or ``PyCode_Addr2Line()`` are not affected.
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Functions decoding directly ``co_lnotab`` should be updated to use a signed
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8-bit integer type for the line number delta, but it's only required to
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support applications using negative line number delta. See
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``Objects/lnotab_notes.txt`` for the ``co_lnotab`` format and how to decode
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it, and see the :pep:`511` for the rationale.
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* The functions in the :mod:`compileall` module now return booleans instead
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of ``1`` or ``0`` to represent success or failure, respectively. Thanks to
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booleans being a subclass of integers, this should only be an issue if you
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were doing identity checks for ``1`` or ``0``. See :issue:`25768`.
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* Reading the :attr:`~urllib.parse.SplitResult.port` attribute of
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:func:`urllib.parse.urlsplit` and :func:`~urllib.parse.urlparse` results
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now raises :exc:`ValueError` for out-of-range values, rather than
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returning :const:`None`. See :issue:`20059`.
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* The :mod:`imp` module now raises a :exc:`DeprecationWarning` instead of
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:exc:`PendingDeprecationWarning`.
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* The following modules have had missing APIs added to their :attr:`__all__`
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attributes to match the documented APIs: :mod:`calendar`, :mod:`csv`,
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:mod:`enum`, :mod:`fileinput`, :mod:`ftplib`, :mod:`logging`,
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:mod:`optparse`, :mod:`tarfile`, :mod:`threading` and
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:mod:`wave`. This means they will export new symbols when ``import *``
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is used. See :issue:`23883`.
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* When performing a relative import, if ``__package__`` does not compare equal
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to ``__spec__.parent`` then :exc:`ImportWarning` is raised.
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(Contributed by Brett Cannon in :issue:`25791`.)
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* When a relative import is performed and no parent package is known, then
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:exc:`ImportError` will be raised. Previously, :exc:`SystemError` could be
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raised. (Contributed by Brett Cannon in :issue:`18018`.)
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* Servers based on the :mod:`socketserver` module, including those
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defined in :mod:`http.server`, :mod:`xmlrpc.server` and
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:mod:`wsgiref.simple_server`, now only catch exceptions derived
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from :exc:`Exception`. Therefore if a request handler raises
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an exception like :exc:`SystemExit` or :exc:`KeyboardInterrupt`,
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:meth:`~socketserver.BaseServer.handle_error` is no longer called, and
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the exception will stop a single-threaded server. (Contributed by
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Martin Panter in :issue:`23430`.)
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Changes in the C API
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--------------------
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* :c:func:`Py_Exit` (and the main interpreter) now override the exit status
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with 120 if flushing buffered data failed. See :issue:`5319`.
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