602 lines
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ReStructuredText
602 lines
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ReStructuredText
****************************
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What's New In Python 3.7
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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 3.7, compared to 3.6.
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For full details, see the :ref:`changelog <changelog>`.
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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 3.7 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 3.7.
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Brevity is key.
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.. PEP-sized items next.
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New Features
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============
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.. _whatsnew37-pep538:
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PEP 538: Legacy C Locale Coercion
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---------------------------------
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An ongoing challenge within the Python 3 series has been determining a sensible
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default strategy for handling the "7-bit ASCII" text encoding assumption
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currently implied by the use of the default C locale on non-Windows platforms.
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:pep:`538` updates the default interpreter command line interface to
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automatically coerce that locale to an available UTF-8 based locale as
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described in the documentation of the new :envvar:`PYTHONCOERCECLOCALE`
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environment variable. Automatically setting ``LC_CTYPE`` this way means that
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both the core interpreter and locale-aware C extensions (such as
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:mod:`readline`) will assume the use of UTF-8 as the default text encoding,
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rather than ASCII.
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The platform support definition in :pep:`11` has also been updated to limit
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full text handling support to suitably configured non-ASCII based locales.
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As part of this change, the default error handler for ``stdin`` and ``stdout``
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is now ``surrogateescape`` (rather than ``strict``) when using any of the
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defined coercion target locales (currently ``C.UTF-8``, ``C.utf8``, and
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``UTF-8``). The default error handler for ``stderr`` continues to be
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``backslashreplace``, regardless of locale.
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Locale coercion is silent by default, but to assist in debugging potentially
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locale related integration problems, explicit warnings (emitted directly on
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``stderr`` can be requested by setting ``PYTHONCOERCECLOCALE=warn``. This
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setting will also cause the Python runtime to emit a warning if the legacy C
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locale remains active when the core interpreter is initialized.
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.. seealso::
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:pep:`538` -- Coercing the legacy C locale to a UTF-8 based locale
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PEP written and implemented by Nick Coghlan.
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.. _whatsnew37-pep553:
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PEP 553: Built-in breakpoint()
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------------------------------
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:pep:`553` describes a new built-in called ``breakpoint()`` which makes it
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easy and consistent to enter the Python debugger. Built-in ``breakpoint()``
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calls ``sys.breakpointhook()``. By default, this latter imports ``pdb`` and
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then calls ``pdb.set_trace()``, but by binding ``sys.breakpointhook()`` to the
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function of your choosing, ``breakpoint()`` can enter any debugger. Or, the
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environment variable :envvar:`PYTHONBREAKPOINT` can be set to the callable of
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your debugger of choice. Set ``PYTHONBREAKPOINT=0`` to completely disable
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built-in ``breakpoint()``.
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.. seealso::
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:pep:`553` -- Built-in breakpoint()
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PEP written and implemented by Barry Warsaw
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.. _whatsnew37-pep539:
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PEP 539: A New C-API for Thread-Local Storage in CPython
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--------------------------------------------------------
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While Python provides a C API for thread-local storage support; the existing
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:ref:`Thread Local Storage (TLS) API <thread-local-storage-api>` has used
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:c:type:`int` to represent TLS keys across all platforms. This has not
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generally been a problem for officially-support platforms, but that is neither
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POSIX-compliant, nor portable in any practical sense.
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:pep:`539` changes this by providing a new :ref:`Thread Specific Storage (TSS)
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API <thread-specific-storage-api>` to CPython which supersedes use of the
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existing TLS API within the CPython interpreter, while deprecating the existing
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API. The TSS API uses a new type :c:type:`Py_tss_t` instead of :c:type:`int`
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to represent TSS keys--an opaque type the definition of which may depend on
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the underlying TLS implementation. Therefore, this will allow to build CPython
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on platforms where the native TLS key is defined in a way that cannot be safely
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cast to :c:type:`int`.
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Note that on platforms where the native TLS key is defined in a way that cannot
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be safely cast to :c:type:`int`, all functions of the existing TLS API will be
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no-op and immediately return failure. This indicates clearly that the old API
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is not supported on platforms where it cannot be used reliably, and that no
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effort will be made to add such support.
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.. seealso::
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:pep:`539` -- A New C-API for Thread-Local Storage in CPython
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PEP written by Erik M. Bray; implementation by Masayuki Yamamoto.
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Other Language Changes
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======================
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* More than 255 arguments can now be passed to a function, and a function can
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now have more than 255 parameters. (Contributed by Serhiy Storchaka in
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:issue:`12844` and :issue:`18896`.)
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* :meth:`bytes.fromhex` and :meth:`bytearray.fromhex` now ignore all ASCII
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whitespace, not only spaces. (Contributed by Robert Xiao in :issue:`28927`.)
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* :exc:`ImportError` now displays module name and module ``__file__`` path when
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``from ... import ...`` fails. (Contributed by Matthias Bussonnier in :issue:`29546`.)
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* Circular imports involving absolute imports with binding a submodule to
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a name are now supported.
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(Contributed by Serhiy Storchaka in :issue:`30024`.)
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* ``object.__format__(x, '')`` is now equivalent to ``str(x)`` rather than
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``format(str(self), '')``.
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(Contributed by Serhiy Storchaka in :issue:`28974`.)
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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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argparse
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--------
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The :meth:`~argparse.ArgumentParser.parse_intermixed_args` supports letting
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the user intermix options and positional arguments on the command line,
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as is possible in many unix commands. It supports most but not all
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argparse features. (Contributed by paul.j3 in :issue:`14191`.)
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binascii
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--------
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The :func:`~binascii.b2a_uu` function now accepts an optional *backtick*
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keyword argument. When it's true, zeros are represented by ``'`'``
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instead of spaces. (Contributed by Xiang Zhang in :issue:`30103`.)
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calendar
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--------
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The class :class:`~calendar.HTMLCalendar` has new class attributes which ease
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the customisation of the CSS classes in the produced HTML calendar.
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(Contributed by Oz Tiram in :issue:`30095`.)
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cgi
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---
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:func:`~cgi.parse_multipart` returns the same results as
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:class:`~FieldStorage` : for non-file fields, the value associated to a key
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is a list of strings, not bytes.
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(Contributed by Pierre Quentel in :issue:`29979`.)
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contextlib
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----------
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:func:`contextlib.asynccontextmanager` has been added. (Contributed by
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Jelle Zijlstra in :issue:`29679`.)
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dis
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---
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The :func:`~dis.dis` function now is able to
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disassemble nested code objects (the code of comprehensions, generator
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expressions and nested functions, and the code used for building nested
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classes). (Contributed by Serhiy Storchaka in :issue:`11822`.)
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distutils
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---------
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README.rst is now included in the list of distutils standard READMEs and
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therefore included in source distributions.
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(Contributed by Ryan Gonzalez in :issue:`11913`.)
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http.server
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-----------
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:class:`~http.server.SimpleHTTPRequestHandler` supports the HTTP
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If-Modified-Since header. The server returns the 304 response status if the
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target file was not modified after the time specified in the header.
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(Contributed by Pierre Quentel in :issue:`29654`.)
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Add the parameter ``directory`` to the :class:`~http.server.SimpleHTTPRequestHandler`
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and the ``--directory`` to the command line of the module :mod:`~http.server`.
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With this parameter, the server serves the specified directory, by default it uses the current working directory.
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(Contributed by Stéphane Wirtel and Julien Palard in :issue:`28707`.)
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locale
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------
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Added another argument *monetary* in :meth:`format_string` of :mod:`locale`.
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If *monetary* is true, the conversion uses monetary thousands separator and
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grouping strings. (Contributed by Garvit in :issue:`10379`.)
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math
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----
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New :func:`~math.remainder` function, implementing the IEEE 754-style remainder
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operation. (Contributed by Mark Dickinson in :issue:`29962`.)
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os
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--
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Added support for :class:`bytes` paths in :func:`~os.fwalk`. (Contributed by
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Serhiy Storchaka in :issue:`28682`.)
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Added support for :ref:`file descriptors <path_fd>` in :func:`~os.scandir`
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on Unix. (Contributed by Serhiy Storchaka in :issue:`25996`.)
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New function :func:`os.register_at_fork` allows registering Python callbacks
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to be executed on a process fork. (Contributed by Antoine Pitrou in
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:issue:`16500`.)
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pdb
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---
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:func:`~pdb.set_trace` now takes an optional ``header`` keyword-only
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argument. If given, this is printed to the console just before debugging
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begins.
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string
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------
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:class:`string.Template` now lets you to optionally modify the regular
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expression pattern for braced placeholders and non-braced placeholders
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separately. (Contributed by Barry Warsaw in :issue:`1198569`.)
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unittest.mock
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-------------
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The :const:`~unittest.mock.sentinel` attributes now preserve their identity
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when they are :mod:`copied <copy>` or :mod:`pickled <pickle>`. (Contributed by
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Serhiy Storchaka in :issue:`20804`.)
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xmlrpc.server
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-------------
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:meth:`register_function` of :class:`xmlrpc.server.SimpleXMLRPCDispatcher` and
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its subclasses can be used as a decorator. (Contributed by Xiang Zhang in
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:issue:`7769`.)
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unicodedata
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-----------
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The internal :mod:`unicodedata` database has been upgraded to use `Unicode 10
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<http://www.unicode.org/versions/Unicode10.0.0/>`_. (Contributed by Benjamin
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Peterson.)
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urllib.parse
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------------
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:func:`urllib.parse.quote` has been updated from RFC 2396 to RFC 3986,
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adding `~` to the set of characters that is never quoted by default.
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(Contributed by Christian Theune and Ratnadeep Debnath in :issue:`16285`.)
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uu
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--
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Function :func:`~uu.encode` now accepts an optional *backtick*
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keyword argument. When it's true, zeros are represented by ``'`'``
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instead of spaces. (Contributed by Xiang Zhang in :issue:`30103`.)
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xml.etree
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---------
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:ref:`ElementPath <elementtree-xpath>` predicates in the :meth:`find`
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methods can now compare text of the current node with ``[. = "text"]``,
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not only text in children. Predicates also allow adding spaces for
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better readability. (Contributed by Stefan Behnel in :issue:`31648`.)
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zipapp
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------
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Function :func:`zipapp.create_archive` now accepts an optional *filter*
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argument to allow the user to select which files should be included in the
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archive, and an optional *compressed* argument to generate a compressed
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archive.
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A command line option ``--compress`` has also been added to support
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compression.
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Optimizations
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=============
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* Added two new opcodes: ``LOAD_METHOD`` and ``CALL_METHOD`` to avoid
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instantiation of bound method objects for method calls, which results
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in method calls being faster up to 20%. (Contributed by Yury Selivanov and
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INADA Naoki in :issue:`26110`.)
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* Searching some unlucky Unicode characters (like Ukrainian capital "Є")
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in a string was to 25 times slower than searching other characters.
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Now it is slower only by 3 times in worst case.
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(Contributed by Serhiy Storchaka in :issue:`24821`.)
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* Fast implementation from standard C library is now used for functions
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:func:`~math.erf` and :func:`~math.erfc` in the :mod:`math` module.
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(Contributed by Serhiy Storchaka in :issue:`26121`.)
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* The :func:`os.fwalk` function has been sped up by 2 times. This was done
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using the :func:`os.scandir` function.
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(Contributed by Serhiy Storchaka in :issue:`25996`.)
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* Optimized case-insensitive matching and searching of :mod:`regular
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expressions <re>`. Searching some patterns can now be up to 20 times faster.
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(Contributed by Serhiy Storchaka in :issue:`30285`.)
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* :func:`re.compile` now converts ``flags`` parameter to int object if
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it is ``RegexFlag``. It is now as fast as Python 3.5, and faster than
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Python 3.6 about 10% depending on the pattern.
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(Contributed by INADA Naoki in :issue:`31671`.)
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* :meth:`selectors.EpollSelector.modify`, :meth:`selectors.PollSelector.modify`
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and :meth:`selectors.DevpollSelector.modify` may be around 10% faster under
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heavy loads. (Contributed by Giampaolo Rodola' in :issue:`30014`)
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Build and C API Changes
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=======================
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* A full copy of libffi is no longer bundled for use when building the
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:mod:`_ctypes <ctypes>` module on non-OSX UNIX platforms. An installed copy
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of libffi is now required when building ``_ctypes`` on such platforms.
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Contributed by Zachary Ware in :issue:`27979`.
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* The fields :c:member:`name` and :c:member:`doc` of structures
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:c:type:`PyMemberDef`, :c:type:`PyGetSetDef`,
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:c:type:`PyStructSequence_Field`, :c:type:`PyStructSequence_Desc`,
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and :c:type:`wrapperbase` are now of type ``const char *`` rather of
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``char *``. (Contributed by Serhiy Storchaka in :issue:`28761`.)
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* The result of :c:func:`PyUnicode_AsUTF8AndSize` and :c:func:`PyUnicode_AsUTF8`
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is now of type ``const char *`` rather of ``char *``. (Contributed by Serhiy
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Storchaka in :issue:`28769`.)
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* The result of :c:func:`PyMapping_Keys`, :c:func:`PyMapping_Values` and
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:c:func:`PyMapping_Items` is now always a list, rather than a list or a
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tuple. (Contributed by Oren Milman in :issue:`28280`.)
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* Added functions :c:func:`PySlice_Unpack` and :c:func:`PySlice_AdjustIndices`.
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(Contributed by Serhiy Storchaka in :issue:`27867`.)
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* :c:func:`PyOS_AfterFork` is deprecated in favour of the new functions
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:c:func:`PyOS_BeforeFork`, :c:func:`PyOS_AfterFork_Parent` and
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:c:func:`PyOS_AfterFork_Child`. (Contributed by Antoine Pitrou in
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:issue:`16500`.)
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* The Windows build process no longer depends on Subversion to pull in external
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sources, a Python script is used to download zipfiles from GitHub instead.
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If Python 3.6 is not found on the system (via ``py -3.6``), NuGet is used to
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download a copy of 32-bit Python for this purpose. (Contributed by Zachary
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Ware in :issue:`30450`.)
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* Support for building ``--without-threads`` is removed.
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(Contributed by Antoine Pitrou in :issue:`31370`.).
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Other CPython Implementation Changes
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====================================
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* Trace hooks may now opt out of receiving ``line`` events from the interpreter
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by setting the new ``f_trace_lines`` attribute to :const:`False` on the frame
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being traced. (Contributed by Nick Coghlan in :issue:`31344`.)
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* Trace hooks may now opt in to receiving ``opcode`` events from the interpreter
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by setting the new ``f_trace_opcodes`` attribute to :const:`True` on the frame
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being traced. (Contributed by Nick Coghlan in :issue:`31344`.)
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Deprecated
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==========
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- Function :c:func:`PySlice_GetIndicesEx` is deprecated and replaced with
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a macro if ``Py_LIMITED_API`` is not set or set to the value between
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``0x03050400`` and ``0x03060000`` (not including) or ``0x03060100`` or
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higher. (Contributed by Serhiy Storchaka in :issue:`27867`.)
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- Deprecated :meth:`format` from :mod:`locale`, use the :meth:`format_string`
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instead. (Contributed by Garvit in :issue:`10379`.)
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- Methods
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:meth:`MetaPathFinder.find_module() <importlib.abc.MetaPathFinder.find_module>`
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(replaced by
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:meth:`MetaPathFinder.find_spec() <importlib.abc.MetaPathFinder.find_spec>`
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) and
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:meth:`PathEntryFinder.find_loader() <importlib.abc.PathEntryFinder.find_loader>`
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(replaced by
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:meth:`PathEntryFinder.find_spec() <importlib.abc.PathEntryFinder.find_spec>`)
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both deprecated in Python 3.4 now emit :exc:`DeprecationWarning`. (Contributed
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by Matthias Bussonnier in :issue:`29576`)
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- Using non-integer value for selecting a plural form in :mod:`gettext` is
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now deprecated. It never correctly worked. (Contributed by Serhiy Storchaka
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in :issue:`28692`.)
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- The :mod:`macpath` is now deprecated and will be removed in Python 3.8.
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Changes in the C API
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--------------------
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- The type of results of :c:func:`PyThread_start_new_thread` and
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:c:func:`PyThread_get_thread_ident`, and the *id* parameter of
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:c:func:`PyThreadState_SetAsyncExc` changed from :c:type:`long` to
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:c:type:`unsigned long`.
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(Contributed by Serhiy Storchaka in :issue:`6532`.)
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- :c:func:`PyUnicode_AsWideCharString` now raises a :exc:`ValueError` if the
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second argument is *NULL* and the :c:type:`wchar_t*` string contains null
|
|
characters. (Contributed by Serhiy Storchaka in :issue:`30708`.)
|
|
|
|
|
|
Windows Only
|
|
------------
|
|
- The python launcher, (py.exe), can accept 32 & 64 bit specifiers **without**
|
|
having to specify a minor version as well. So ``py -3-32`` and ``py -3-64``
|
|
become valid as well as ``py -3.7-32``, also the -*m*-64 and -*m.n*-64 forms
|
|
are now accepted to force 64 bit python even if 32 bit would have otherwise
|
|
been used. If the specified version is not available py.exe will error exit.
|
|
(Contributed by Steve Barnes in :issue:`30291`.)
|
|
|
|
- The launcher can be run as "py -0" to produce a list of the installed pythons,
|
|
*with default marked with an asterix*. Running "py -0p" will include the paths.
|
|
If py is run with a version specifier that cannot be matched it will also print
|
|
the *short form* list of available specifiers.
|
|
(Contributed by Steve Barnes in :issue:`30362`.)
|
|
|
|
Removed
|
|
=======
|
|
|
|
API and Feature Removals
|
|
------------------------
|
|
|
|
* Unknown escapes consisting of ``'\'`` and an ASCII letter in replacement
|
|
templates for :func:`re.sub` were deprecated in Python 3.5, and will now
|
|
cause an error.
|
|
|
|
* Removed support of the *exclude* argument in :meth:`tarfile.TarFile.add`.
|
|
It was deprecated in Python 2.7 and 3.2. Use the *filter* argument instead.
|
|
|
|
* The ``splitunc()`` function in the :mod:`ntpath` module was deprecated in
|
|
Python 3.1, and has now been removed. Use the :func:`~os.path.splitdrive`
|
|
function instead.
|
|
|
|
* :func:`collections.namedtuple` no longer supports the *verbose* parameter
|
|
or ``_source`` attribute which showed the generated source code for the
|
|
named tuple class. This was part of an optimization designed to speed-up
|
|
class creation. (Contributed by Jelle Zijlstra with further improvements
|
|
by INADA Naoki, Serhiy Storchaka, and Raymond Hettinger in :issue:`28638`.)
|
|
|
|
* Functions :func:`bool`, :func:`float`, :func:`list` and :func:`tuple` no
|
|
longer take keyword arguments. The first argument of :func:`int` can now
|
|
be passed only as positional argument.
|
|
|
|
* Removed previously deprecated in Python 2.4 classes ``Plist``, ``Dict`` and
|
|
``_InternalDict`` in the :mod:`plistlib` module. Dict values in the result
|
|
of functions :func:`~plistlib.readPlist` and
|
|
:func:`~plistlib.readPlistFromBytes` are now normal dicts. You no longer
|
|
can use attribute access to access items of these dictionaries.
|
|
|
|
|
|
Porting to Python 3.7
|
|
=====================
|
|
|
|
This section lists previously described changes and other bugfixes
|
|
that may require changes to your code.
|
|
|
|
|
|
Changes in the Python API
|
|
-------------------------
|
|
|
|
* :meth:`pkgutil.walk_packages` now raises ValueError if *path* is a string.
|
|
Previously an empty list was returned. (Contributed by Sanyam Khurana in
|
|
:issue:`24744`.)
|
|
|
|
* A format string argument for :meth:`string.Formatter.format`
|
|
is now :ref:`positional-only <positional-only_parameter>`.
|
|
Passing it as a keyword argument was deprecated in Python 3.5. (Contributed
|
|
by Serhiy Storchaka in :issue:`29193`.)
|
|
|
|
* Attributes :attr:`~http.cookies.Morsel.key`,
|
|
:attr:`~http.cookies.Morsel.value` and
|
|
:attr:`~http.cookies.Morsel.coded_value` of class
|
|
:class:`http.cookies.Morsel` are now read-only.
|
|
Assigning to them was deprecated in Python 3.5.
|
|
Use the :meth:`~http.cookies.Morsel.set` method for setting them.
|
|
(Contributed by Serhiy Storchaka in :issue:`29192`.)
|
|
|
|
* ``Module``, ``FunctionDef``, ``AsyncFunctionDef``, and
|
|
``ClassDef`` AST nodes now have a new ``docstring`` field.
|
|
The first statement in their body is not considered as a docstring
|
|
anymore. ``co_firstlineno`` and ``co_lnotab`` of code object for class
|
|
and module are affected by this change. (Contributed by INADA Naoki and
|
|
Eugene Toder in :issue:`29463`.)
|
|
|
|
* The *mode* argument of :func:`os.makedirs` no longer affects the file
|
|
permission bits of newly-created intermediate-level directories.
|
|
To set their file permission bits you can set the umask before invoking
|
|
``makedirs()``.
|
|
(Contributed by Serhiy Storchaka in :issue:`19930`.)
|
|
|
|
* The :attr:`struct.Struct.format` type is now :class:`str` instead of
|
|
:class:`bytes`. (Contributed by Victor Stinner in :issue:`21071`.)
|
|
|
|
* Due to internal changes in :mod:`socket` you won't be able to
|
|
:func:`socket.fromshare` a socket :func:`~socket.socket.share`-ed in older
|
|
Python versions.
|
|
|
|
* ``repr`` for :class:`datetime.timedelta` has changed to include keyword arguments
|
|
in the output. (Contributed by Utkarsh Upadhyay in :issue:`30302`.)
|
|
|
|
|
|
Changes in the C API
|
|
--------------------
|
|
|
|
* The function :c:func:`PySlice_GetIndicesEx` is considered not safe for
|
|
resizable sequences. If the slice indices are not instances of :class:`int`,
|
|
but objects that implement the :meth:`!__index__` method, the sequence can be
|
|
resized after passing its length to :c:func:`!PySlice_GetIndicesEx`. This
|
|
can lead to returning indices out of the length of the sequence. For
|
|
avoiding possible problems use new functions :c:func:`PySlice_Unpack` and
|
|
:c:func:`PySlice_AdjustIndices`.
|
|
(Contributed by Serhiy Storchaka in :issue:`27867`.)
|
|
|
|
|
|
CPython bytecode changes
|
|
------------------------
|
|
|
|
* Added two new opcodes: :opcode:`LOAD_METHOD` and :opcode:`CALL_METHOD`.
|
|
(Contributed by Yury Selivanov and INADA Naoki in :issue:`26110`.)
|