**************************** What's New In Python 3.5 **************************** :Release: |release| :Date: |today| :Editors: Elvis Pranskevichus , Yury Selivanov .. Rules for maintenance: * Anyone can add text to this document. Do not spend very much time on the wording of your changes, because your text will probably get rewritten to some degree. * The maintainer will go through Misc/NEWS periodically and add changes; it's therefore more important to add your changes to Misc/NEWS than to this file. * This is not a complete list of every single change; completeness is the purpose of Misc/NEWS. Some changes I consider too small or esoteric to include. If such a change is added to the text, I'll just remove it. (This is another reason you shouldn't spend too much time on writing your addition.) * If you want to draw your new text to the attention of the maintainer, add 'XXX' to the beginning of the paragraph or section. * It's OK to just add a fragmentary note about a change. For example: "XXX Describe the transmogrify() function added to the socket module." The maintainer will research the change and write the necessary text. * You can comment out your additions if you like, but it's not necessary (especially when a final release is some months away). * Credit the author of a patch or bugfix. Just the name is sufficient; the e-mail address isn't necessary. * It's helpful to add the bug/patch number as a comment: XXX Describe the transmogrify() function added to the socket module. (Contributed by P.Y. Developer in :issue:`12345`.) This saves the maintainer the effort of going through the Mercurial log when researching a change. This article explains the new features in Python 3.5, compared to 3.4. For full details, see the :source:`Misc/NEWS` file. .. note:: Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.5 moves towards release, so it's worth checking back even after reading earlier versions. .. seealso:: :pep:`478` - Python 3.5 Release Schedule Summary -- Release highlights ============================= .. This section singles out the most important changes in Python 3.5. Brevity is key. New syntax features: * :pep:`492`, coroutines with async and await syntax. * :pep:`465`, a new matrix multiplication operator: ``a @ b``. * :pep:`448`, additional unpacking generalizations. New library modules: * :mod:`typing`: :ref:`Type Hints ` (:pep:`484`). * :mod:`zipapp`: :ref:`Improving Python ZIP Application Support ` (:pep:`441`). New built-in features: * ``bytes % args``, ``bytearray % args``: :pep:`461` - Adding ``%`` formatting to bytes and bytearray. * ``b'\xf0\x9f\x90\x8d'.hex()``, ``bytearray(b'\xf0\x9f\x90\x8d').hex()``, ``memoryview(b'\xf0\x9f\x90\x8d').hex()``: :issue:`9951` - A ``hex`` method has been added to bytes, bytearray, and memoryview. * :class:`memoryview` (including multi-dimensional) now supports tuple indexing. (Contributed by Antoine Pitrou in :issue:`23632`.) * Generators have new ``gi_yieldfrom`` attribute, which returns the object being iterated by ``yield from`` expressions. (Contributed by Benno Leslie and Yury Selivanov in :issue:`24450`.) * New :exc:`RecursionError` exception. (Contributed by Georg Brandl in :issue:`19235`.) * New :exc:`StopAsyncIteration` exception. (Contributed by Yury Selivanov in :issue:`24017`. See also :pep:`492`.) CPython implementation improvements: * When the ``LC_TYPE`` locale is the POSIX locale (``C`` locale), :py:data:`sys.stdin` and :py:data:`sys.stdout` are now using the ``surrogateescape`` error handler, instead of the ``strict`` error handler. (Contributed by Victor Stinner in :issue:`19977`.) * ``.pyo`` files are no longer used and have been replaced by a more flexible scheme that inclides the optimization level explicitly in ``.pyc`` name. (:pep:`488`) * Builtin and extension modules are now initialized in a multi-phase process, which is similar to how Python modules are loaded. (:pep:`489`). Significant improvements in standard library: * :class:`collections.OrderedDict` is now :ref:`implemented in C `, which makes it 4 to 100 times faster. * :mod:`ssl` module gained :ref:`support for Memory BIO `, which decouples SSL protocol handling from network IO. * :mod:`traceback` module has been significantly :ref:`enhanced ` for improved performance and developer convenience. * The new :func:`os.scandir` function provides a :ref:`better and significantly faster way ` of directory traversal. * :func:`functools.lru_cache` has been largely :ref:`reimplemented in C `, yielding much better performance. * The new :func:`subprocess.run` function provides a :ref:`streamlined way to run subprocesses `. Security improvements: * SSLv3 is now disabled throughout the standard library. It can still be enabled by instantiating a :class:`ssl.SSLContext` manually. (See :issue:`22638` for more details; this change was backported to CPython 3.4 and 2.7.) * HTTP cookie parsing is now stricter, in order to protect against potential injection attacks. (Contributed by Antoine Pitrou in :issue:`22796`.) Windows improvements: * A new installer for Windows has replaced the old MSI. See :ref:`using-on-windows` for more information. * Windows builds now use Microsoft Visual C++ 14.0, and extension modules should use the same. Please read on for a comprehensive list of user-facing changes, including many other smaller improvements, CPython optimizations, deprecations, and potential porting issues. New Features ============ .. _whatsnew-pep-492: PEP 492 - Coroutines with async and await syntax ------------------------------------------------ :pep:`492` greatly improves support for asynchronous programming in Python by adding :term:`awaitable objects `, :term:`coroutine functions `, :term:`asynchronous iteration `, and :term:`asynchronous context managers `. Coroutine functions are declared using the new :keyword:`async def` syntax:: >>> async def coro(): ... return 'spam' Inside a coroutine function, the new :keyword:`await` expression can be used to suspend coroutine execution until the result is available. Any object can be *awaited*, as long as it implements the :term:`awaitable` protocol by defining the :meth:`__await__` method. PEP 492 also adds :keyword:`async for` statement for convenient iteration over asynchronous iterables. An example of a simple HTTP client written using the new syntax:: import asyncio async def http_get(domain): reader, writer = await asyncio.open_connection(domain, 80) writer.write(b'\r\n'.join([ b'GET / HTTP/1.1', b'Host: %b' % domain.encode('latin-1'), b'Connection: close', b'', b'' ])) async for line in reader: print('>>>', line) writer.close() loop = asyncio.get_event_loop() try: loop.run_until_complete(http_get('example.com')) finally: loop.close() Similarly to asynchronous iteration, there is a new syntax for asynchronous context managers. The following script:: import asyncio async def coro(name, lock): print('coro {}: waiting for lock'.format(name)) async with lock: print('coro {}: holding the lock'.format(name)) await asyncio.sleep(1) print('coro {}: releasing the lock'.format(name)) loop = asyncio.get_event_loop() lock = asyncio.Lock() coros = asyncio.gather(coro(1, lock), coro(2, lock)) try: loop.run_until_complete(coros) finally: loop.close() will output:: coro 2: waiting for lock coro 2: holding the lock coro 1: waiting for lock coro 2: releasing the lock coro 1: holding the lock coro 1: releasing the lock Note that both :keyword:`async for` and :keyword:`async with` can only be used inside a coroutine function declared with :keyword:`async def`. Coroutine functions are intended to be run inside a compatible event loop, such as :class:`asyncio.Loop`. .. seealso:: :pep:`492` -- Coroutines with async and await syntax PEP written and implemented by Yury Selivanov. .. _whatsnew-pep-465: PEP 465 - A dedicated infix operator for matrix multiplication -------------------------------------------------------------- :pep:`465` adds the ``@`` infix operator for matrix multiplication. Currently, no builtin Python types implement the new operator, however, it can be implemented by defining :meth:`__matmul__`, :meth:`__rmatmul__`, and :meth:`__imatmul__` for regular, reflected, and in-place matrix multiplication. The semantics of these methods is similar to that of methods defining other infix arithmetic operators. Matrix multiplication is a notably common operation in many fields of mathematics, science, engineering, and the addition of ``@`` allows writing cleaner code:: S = (H @ beta - r).T @ inv(H @ V @ H.T) @ (H @ beta - r) instead of:: S = dot((dot(H, beta) - r).T, dot(inv(dot(dot(H, V), H.T)), dot(H, beta) - r)) An upcoming release of NumPy 1.10 will add support for the new operator:: >>> import numpy >>> x = numpy.ones(3) >>> x array([ 1., 1., 1.]) >>> m = numpy.eye(3) >>> m array([[ 1., 0., 0.], [ 0., 1., 0.], [ 0., 0., 1.]]) >>> x @ m array([ 1., 1., 1.]) .. seealso:: :pep:`465` -- A dedicated infix operator for matrix multiplication PEP written by Nathaniel J. Smith; implemented by Benjamin Peterson. .. _whatsnew-pep-448: PEP 448 - Additional Unpacking Generalizations ---------------------------------------------- :pep:`448` extends the allowed uses of the ``*`` iterable unpacking operator and ``**`` dictionary unpacking operator. It is now possible to use an arbitrary number of unpackings in function calls:: >>> print(*[1], *[2], 3, *[4, 5]) 1 2 3 4 5 >>> def fn(a, b, c, d): ... print(a, b, c, d) ... >>> fn(**{'a': 1, 'c': 3}, **{'b': 2, 'd': 4}) 1 2 3 4 Similarly, tuple, list, set, and dictionary displays allow multiple unpackings:: >>> *range(4), 4 (0, 1, 2, 3, 4) >>> [*range(4), 4] [0, 1, 2, 3, 4] >>> {*range(4), 4, *(5, 6, 7)} {0, 1, 2, 3, 4, 5, 6, 7} >>> {'x': 1, **{'y': 2}} {'x': 1, 'y': 2} .. seealso:: :pep:`448` -- Additional Unpacking Generalizations PEP written by Joshua Landau; implemented by Neil Girdhar, Thomas Wouters, and Joshua Landau. .. _whatsnew-pep-461: PEP 461 - % formatting support for bytes and bytearray ------------------------------------------------------ :pep:`461` adds support for ``%`` :ref:`interpolation operator ` to :class:`bytes` and :class:`bytearray`. While interpolation is usually thought of as a string operation, there are cases where interpolation on ``bytes`` or ``bytearrays`` make sense, and the work needed to make up for this missing functionality detracts from the overall readability of the code. This issue is particularly important when dealing with wire format protocols, which are often a mixture of binary and ASCII compatible text. Examples:: >>> b'Hello %b!' % b'World' b'Hello World!' >>> b'x=%i y=%f' % (1, 2.5) b'x=1 y=2.500000' Unicode is not allowed for ``%b``, but it is accepted by ``%a`` (equivalent of ``repr(obj).encode('ascii', 'backslashreplace')``):: >>> b'Hello %b!' % 'World' Traceback (most recent call last): File "", line 1, in TypeError: %b requires bytes, or an object that implements __bytes__, not 'str' >>> b'price: %a' % '10€' b"price: '10\\u20ac'" Note that ``%s`` and ``%r`` conversion types, although supported, should only be used in codebases that need compatibility with Python 2. .. seealso:: :pep:`461` -- Adding % formatting to bytes and bytearray PEP written by Ethan Furman; implemented by Neil Schemenauer and Ethan Furman. .. _whatsnew-pep-484: PEP 484 - Type Hints -------------------- Function annotation syntax has been a Python feature since version 3.0 (:pep:`3107`), however the semantics of annotations has been left undefined. Experience has shown that the majority of function annotation uses were to provide type hints to function parameters and return values. It became evident that it would be beneficial for Python users, if the standard library included the base definitions and tools for type annotations. :pep:`484` introduces a :term:`provisional module ` to provide these standard definitions and tools, along with some conventions for situations where annotations are not available. For example, here is a simple function whose argument and return type are declared in the annotations:: def greeting(name: str) -> str: return 'Hello ' + name While these annotations are available at runtime through the usual :attr:`__annotations__` attribute, *no automatic type checking happens at runtime*. Instead, it is assumed that a separate off-line type checker will be used for on-demand source code analysis. The type system supports unions, generic types, and a special type named :class:`~typing.Any` which is consistent with (i.e. assignable to and from) all types. .. seealso:: * :mod:`typing` module documentation * :pep:`484` -- Type Hints PEP written by Guido van Rossum, Jukka Lehtosalo, and Łukasz Langa; implemented by Guido van Rossum. * :pep:`483` -- The Theory of Type Hints PEP written by Guido van Rossum .. _whatsnew-pep-471: PEP 471 - os.scandir() function -- a better and faster directory iterator ------------------------------------------------------------------------- :pep:`471` adds a new directory iteration function, :func:`os.scandir`, to the standard library. Additionally, :func:`os.walk` is now implemented using ``scandir``, which makes it 3 to 5 times faster on POSIX systems and 7 to 20 times faster on Windows systems. This is largely achieved by greatly reducing the number of calls to :func:`os.stat` required to walk a directory tree. Additionally, ``scandir`` returns an iterator, as opposed to returning a list of file names, which improves memory efficiency when iterating over very large directories. The following example shows a simple use of :func:`os.scandir` to display all the files (excluding directories) in the given *path* that don't start with ``'.'``. The :meth:`entry.is_file ` call will generally not make an additional system call:: for entry in os.scandir(path): if not entry.name.startswith('.') and entry.is_file(): print(entry.name) .. seealso:: :pep:`471` -- os.scandir() function -- a better and faster directory iterator PEP written and implemented by Ben Hoyt with the help of Victor Stinner. .. _whatsnew-pep-475: PEP 475: Retry system calls failing with EINTR ---------------------------------------------- A :py:data:`~errno.EINTR` error code is returned whenever a system call, that is waiting for I/O, is interrupted by a signal. Previously, Python would raise :exc:`InterruptedError` in such case. This meant that, when writing a Python application, the developer had two choices: #. Ignore the ``InterruptedError``. #. Handle the ``InterruptedError`` and attempt to restart the interrupted system call at every call site. The first option makes an application fail intermittently. The second option adds a large amount of boilerplate that makes the code nearly unreadable. Compare:: print("Hello World") and:: while True: try: print("Hello World") break except InterruptedError: continue :pep:`475` implements automatic retry of system calls on ``EINTR``. This removes the burden of dealing with ``EINTR`` or :exc:`InterruptedError` in user code in most situations and makes Python programs, including the standard library, more robust. Note that the system call is only retried if the signal handler does not raise an exception. Below is a list of functions which are now retried when interrupted by a signal: * :func:`open`, :func:`os.open`, :func:`io.open`; * functions of the :mod:`faulthandler` module; * :mod:`os` functions: :func:`~os.fchdir`, :func:`~os.fchmod`, :func:`~os.fchown`, :func:`~os.fdatasync`, :func:`~os.fstat`, :func:`~os.fstatvfs`, :func:`~os.fsync`, :func:`~os.ftruncate`, :func:`~os.mkfifo`, :func:`~os.mknod`, :func:`~os.posix_fadvise`, :func:`~os.posix_fallocate`, :func:`~os.pread`, :func:`~os.pwrite`, :func:`~os.read`, :func:`~os.readv`, :func:`~os.sendfile`, :func:`~os.wait3`, :func:`~os.wait4`, :func:`~os.wait`, :func:`~os.waitid`, :func:`~os.waitpid`, :func:`~os.write`, :func:`~os.writev`; * special cases: :func:`os.close` and :func:`os.dup2` now ignore :py:data:`~errno.EINTR` error, the syscall is not retried (see the PEP for the rationale); * :mod:`select` functions: :func:`~select.devpoll.poll`, :func:`~select.epoll.poll`, :func:`~select.kqueue.control`, :func:`~select.poll.poll`, :func:`~select.select`; * :func:`socket.socket` methods: :meth:`~socket.socket.accept`, :meth:`~socket.socket.connect` (except for non-blocking sockets), :meth:`~socket.socket.recv`, :meth:`~socket.socket.recvfrom`, :meth:`~socket.socket.recvmsg`, :meth:`~socket.socket.send`, :meth:`~socket.socket.sendall`, :meth:`~socket.socket.sendmsg`, :meth:`~socket.socket.sendto`; * :func:`signal.sigtimedwait`, :func:`signal.sigwaitinfo`; * :func:`time.sleep`. .. seealso:: :pep:`475` -- Retry system calls failing with EINTR PEP and implementation written by Charles-François Natali and Victor Stinner, with the help of Antoine Pitrou (the French connection). .. _whatsnew-pep-479: PEP 479: Change StopIteration handling inside generators -------------------------------------------------------- The interaction of generators and :exc:`StopIteration` in Python 3.4 and earlier was somewhat surprising, and could conceal obscure bugs. Previously, ``StopIteration`` raised accidentally inside a generator function was interpreted as the end of the iteration by the loop construct driving the generator. :pep:`479` changes the behavior of generators: when a ``StopIteration`` exception is raised inside a generator, it is replaced with a :exc:`RuntimeError` before it exits the generator frame. The main goal of this change is to ease debugging in the situation where an unguarded :func:`next` call raises ``StopIteration`` and causes the iteration controlled by the generator to terminate silently. This is particularly pernicious in combination with the ``yield from`` construct. This is a backwards incompatible change, so to enable the new behavior, a :term:`__future__` import is necessary:: from __future__ import generator_stop Without a ``__future__`` import, a :exc:`PendingDeprecationWarning` will be raised whenever a ``StopIteration`` exception is raised inside a generator. .. seealso:: :pep:`479` -- Change StopIteration handling inside generators PEP written by Chris Angelico and Guido van Rossum. Implemented by Chris Angelico, Yury Selivanov and Nick Coghlan. .. _whatsnew-pep-486: PEP 486: Make the Python Launcher aware of virtual environments --------------------------------------------------------------- :pep:`486` makes the Windows launcher (see :pep:`397`) aware of an active virtual environment. When the default interpreter would be used and the ``VIRTUAL_ENV`` environment variable is set, the interpreter in the virtual environment will be used. .. seealso:: :pep:`486` -- Make the Python Launcher aware of virtual environments PEP written and implemented by Paul Moore. .. _whatsnew-pep-488: PEP 488: Elimination of PYO files --------------------------------- :pep:`488` does away with the concept of ``.pyo`` files. This means that ``.pyc`` files represent both unoptimized and optimized bytecode. To prevent the need to constantly regenerate bytecode files, ``.pyc`` files now have an optional ``opt-`` tag in their name when the bytecode is optimized. This has the side-effect of no more bytecode file name clashes when running under either :option:`-O` or :option:`-OO`. Consequently, bytecode files generated from :option:`-O`, and :option:`-OO` may now exist simultaneously. :func:`importlib.util.cache_from_source` has an updated API to help with this change. .. seealso:: :pep:`488` -- Elimination of PYO files PEP written and implemented by Brett Cannon. .. _whatsnew-pep-489: PEP 489: Multi-phase extension module initialization ---------------------------------------------------- :pep:`489` updates extension module initialization to take advantage of the two step module loading mechanism introduced by :pep:`451` in Python 3.4. This change brings the import semantics of extension modules that opt-in to using the new mechanism much closer to those of Python source and bytecode modules, including the ability to use any valid identifier as a module name, rather than being restricted to ASCII. .. seealso:: :pep:`489` -- Multi-phase extension module initialization PEP written by Petr Viktorin, Stefan Behnel, and Nick Coghlan; implemented by Petr Viktorin. .. _whatsnew-pep-485: PEP 485: A function for testing approximate equality ---------------------------------------------------- :pep:`485` adds the :func:`math.isclose` and :func:`cmath.isclose` functions which tell whether two values are approximately equal or "close" to each other. Whether or not two values are considered close is determined according to given absolute and relative tolerances. Relative tolerance is the maximum allowed difference between ``isclose()`` arguments, relative to the larger absolute value:: >>> import math >>> a = 5.0 >>> b = 4.99998 >>> math.isclose(a, b, rel_tol=1e-5) True >>> math.isclose(a, b, rel_tol=1e-6) False It is also possible to compare two values using absolute tolerance, which must be a non-negative value:: >>> import math >>> a = 5.0 >>> b = 4.99998 >>> math.isclose(a, b, abs_tol=0.00003) True >>> math.isclose(a, b, abs_tol=0.00001) False .. seealso:: :pep:`485` -- A function for testing approximate equality PEP written by Christopher Barker; implemented by Chris Barker and Tal Einat. Other Language Changes ====================== Some smaller changes made to the core Python language are: * Added the ``"namereplace"`` error handlers. The ``"backslashreplace"`` error handlers now works with decoding and translating. (Contributed by Serhiy Storchaka in :issue:`19676` and :issue:`22286`.) * The :option:`-b` option now affects comparisons of :class:`bytes` with :class:`int`. (Contributed by Serhiy Storchaka in :issue:`23681`.) * New Kazakh :ref:`codec ` ``kz1048``. (Contributed by Serhiy Storchaka in :issue:`22682`.) * Property docstrings are now writable. This is especially useful for :func:`collections.namedtuple` docstrings. (Contributed by Berker Peksag in :issue:`24064`.) * New Tajik :ref:`codec ` ``koi8_t``. (Contributed by Serhiy Storchaka in :issue:`22681`.) * Circular imports involving relative imports are now supported. (Contributed by Brett Cannon and Antoine Pitrou in :issue:`17636`.) New Modules =========== typing ------ The new :mod:`typing` :term:`provisional ` module provides standard definitions and tools for function type annotations. See :ref:`Type Hints ` for more information. .. _whatsnew-zipapp: zipapp ------ The new :mod:`zipapp` module (specified in :pep:`441`) provides an API and command line tool for creating executable Python Zip Applications, which were introduced in Python 2.6 in :issue:`1739468`, but which were not well publicized, either at the time or since. With the new module, bundling your application is as simple as putting all the files, including a ``__main__.py`` file, into a directory ``myapp`` and running:: $ python -m zipapp myapp $ python myapp.pyz The module implementation has been contributed by Paul Moore in :issue:`23491`. .. seealso:: :pep:`441` -- Improving Python ZIP Application Support Improved Modules ================ argparse -------- The :class:`~argparse.ArgumentParser` class now allows to disable :ref:`abbreviated usage ` of long options by setting :ref:`allow_abbrev` to ``False``. (Contributed by Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson in :issue:`14910`.) asyncio ------- Since :mod:`asyncio` module is :term:`provisional `, all changes introduced in Python 3.5 have also been backported to Python 3.4.x. Notable changes in :mod:`asyncio` module since Python 3.4.0: * A new debugging APIs: :meth:`loop.set_debug() ` and :meth:`loop.get_debug() `. (Contributed by Victor Stinner.) * The proactor event loop now supports SSL. (Contributed by Antoine Pitrou and Victor Stinner in :issue:`22560`.) * A new :meth:`loop.is_closed() ` to check if the event loop is closed. (Contributed by Victor Stinner in :issue:`21326`.) * A new :meth:`loop.create_task() ` to conveniently create and schedule a new :class:`~asyncio.Task` for a coroutine. The ``create_task`` method is also used by all asyncio functions that wrap coroutines into tasks: :func:`asyncio.wait`, :func:`asyncio.gather`, etc. (Contributed by Victor Stinner.) * A new :meth:`WriteTransport.get_write_buffer_limits ` method to inquire for *high-* and *low-* water limits of the flow control. (Contributed by Victor Stinner.) * The :func:`~asyncio.async` function is deprecated in favor of :func:`~asyncio.ensure_future`. (Contributed by Yury Selivanov.) * New :meth:`loop.set_task_factory ` and :meth:`loop.set_task_factory ` to customize the task factory that :meth:`loop.create_task() ` method uses. (Contributed by Yury Selivanov.) * New :meth:`Queue.join ` and :meth:`Queue.task_done ` queue methods. (Contributed by Victor Stinner.) * The ``JoinableQueue`` class was removed, in favor of the :class:`asyncio.Queue` class. (Contributed by Victor Stinner.) bz2 --- The :meth:`BZ2Decompressor.decompress ` method now accepts an optional *max_length* argument to limit the maximum size of decompressed data. (Contributed by Nikolaus Rath in :issue:`15955`.) cgi --- The :class:`~cgi.FieldStorage` class now supports the context management protocol. (Contributed by Berker Peksag in :issue:`20289`.) csv --- :meth:`Writer.writerow ` now supports arbitrary iterables, not just sequences. (Contributed by Serhiy Storchaka in :issue:`23171`.) cmath ----- A new function :func:`~cmath.isclose` provides a way to test for approximate equality. (Contributed by Chris Barker and Tal Einat in :issue:`24270`.) code ---- The :func:`InteractiveInterpreter.showtraceback ` method now prints the full chained traceback, just like the interactive interpreter. (Contributed by Claudiu Popa in :issue:`17442`.) collections ----------- .. _whatsnew-ordereddict: The :class:`~collections.OrderedDict` class is now implemented in C, which makes it 4 to 100 times faster. (Contributed by Eric Snow in :issue:`16991`.) :meth:`OrderedDict.items `, :meth:`OrderedDict.keys `, :meth:`OrderedDict.values ` views now support :func:`reversed` iteration. (Contributed by Serhiy Storchaka in :issue:`19505`.) The :class:`~collections.deque` class now defines :meth:`~collections.deque.index`, :meth:`~collections.deque.insert`, and :meth:`~collections.deque.copy`, as well as supports ``+`` and ``*`` operators. This allows deques to be recognized as a :class:`~collections.abc.MutableSequence` and improves their substitutability for lists. (Contributed by Raymond Hettinger :issue:`23704`.) Docstrings produced by :func:`~collections.namedtuple` can now be updated:: Point = namedtuple('Point', ['x', 'y']) Point.__doc__ = 'ordered pair' Point.x.__doc__ = 'abscissa' Point.y.__doc__ = 'ordinate' (Contributed by Berker Peksag in :issue:`24064`.) The :class:`~collections.UserString` class now implements :meth:`__getnewargs__`, :meth:`__rmod__`, :meth:`~str.casefold`, :meth:`~str.format_map`, :meth:`~str.isprintable`, and :meth:`~str.maketrans` methods to match corresponding methods of :class:`str`. (Contributed by Joe Jevnik in :issue:`22189`.) collections.abc --------------- The :meth:`Sequence.index ` method now accepts *start* and *stop* arguments to match the corresponding methods of :class:`tuple`, :class:`list`, etc. (Contributed by Devin Jeanpierre in :issue:`23086`.) A new :class:`~collections.abc.Generator` abstract base class. (Contributed by Stefan Behnel in :issue:`24018`.) New :class:`~collections.abc.Awaitable` :class:`~collections.abc.Coroutine`, :class:`~collections.abc.AsyncIterator`, and :class:`~collections.abc.AsyncIterable` abstract base classes. (Contributed by Yury Selivanov in :issue:`24184`.) compileall ---------- A new :mod:`compileall` option, ``-j N``, allows to run ``N`` workers sumultaneously to perform parallel bytecode compilation. The :func:`~compileall.compile_dir` function has a corresponding ``workers`` parameter. (Contributed by Claudiu Popa in :issue:`16104`.) Another new option, ``-r``, allows to control the maximum recursion level for subdirectories. (Contributed by Claudiu Popa in :issue:`19628`.) The ``-q`` command line option can now be specified more than once, in which case all output, including errors, will be suppressed. The corresponding ``quiet`` parameter in :func:`~compileall.compile_dir`, :func:`~compileall.compile_file`, and :func:`~compileall.compile_path` can now accept an integer value indicating the level of output suppression. (Contributed by Thomas Kluyver in :issue:`21338`.) concurrent.futures ------------------ The :meth:`Executor.map ` method now accepts a *chunksize* argument to allow batching of tasks to improve performance when :meth:`~concurrent.futures.ProcessPoolExecutor` is used. (Contributed by Dan O'Reilly in :issue:`11271`.) A number of workers in :class:`~concurrent.futures.ThreadPoolExecutor` is optional now. The default value equals to 5 times the number of CPUs. (Contributed by Claudiu Popa in :issue:`21527`.) configparser ------------ Config parsers can be customized by providing a dictionary of converters in the constructor, or All converters defined in config parser (either by subclassing or by providing in a constructor) will be available on all section proxies. Example:: >>> import configparser >>> conv = {} >>> conv['list'] = lambda v: [e.strip() for e in v.split() if e.strip()] >>> cfg = configparser.ConfigParser(converters=conv) >>> cfg.read_string(""" ... [s] ... list = a b c d e f g ... """) >>> cfg.get('s', 'list') 'a b c d e f g' >>> cfg.getlist('s', 'list') ['a', 'b', 'c', 'd', 'e', 'f', 'g'] (Contributed by Łukasz Langa in :issue:`18159`.) contextlib ---------- The new :func:`~contextlib.redirect_stderr` context manager (similar to :func:`~contextlib.redirect_stdout`) makes it easier for utility scripts to handle inflexible APIs that write their output to :data:`sys.stderr` and don't provide any options to redirect it:: >>> import contextlib, io, logging >>> f = io.StringIO() >>> with contextlib.redirect_stderr(f): ... logging.warning('warning') ... >>> f.getvalue() 'WARNING:root:warning\n' (Contributed by Berker Peksag in :issue:`22389`.) curses ------ The new :func:`~curses.update_lines_cols` function updates :envvar:`LINES` and :envvar:`COLS` environment variables. This is useful for detecting manual screen resize. (Contributed by Arnon Yaari in :issue:`4254`.) dbm --- :func:`dumb.open ` always creates a new database when the flag has the value ``'n'``. (Contributed by Claudiu Popa in :issue:`18039`.) difflib ------- The charset of HTML documents generated by :meth:`HtmlDiff.make_file ` can now be customized by using a new *charset* keyword-only argument. The default charset of HTML document changed from ``"ISO-8859-1"`` to ``"utf-8"``. (Contributed by Berker Peksag in :issue:`2052`.) The :func:`~difflib.diff_bytes` function can now compare lists of byte strings. This fixes a regression from Python 2. (Contributed by Terry J. Reedy and Greg Ward in :issue:`17445`.) distutils --------- Both ``build`` and ``build_ext`` commands now accept a ``-j`` option to enable parallel building of extension modules. (Contributed by Antoine Pitrou in :issue:`5309`.) The :mod:`distutils` module now supports ``xz`` compression, and can be enabled by passing ``xztar`` as an argument to ``bdist --format``. (Contributed by Serhiy Storchaka in :issue:`16314`.) doctest ------- The :func:`~doctest.DocTestSuite` function returns an empty :class:`unittest.TestSuite` if *module* contains no docstrings instead of raising :exc:`ValueError`. (Contributed by Glenn Jones in :issue:`15916`.) email ----- A new policy option :attr:`Policy.mangle_from_ ` controls whether or not lines that start with ``"From "`` in email bodies are prefixed with a ``">"`` character by generators. The default is ``True`` for :attr:`~email.policy.compat32` and ``False`` for all other policies. (Contributed by Milan Oberkirch in :issue:`20098`.) A new :meth:`Message.get_content_disposition ` method provides easy access to a canonical value for the :mailheader:`Content-Disposition` header. (Contributed by Abhilash Raj in :issue:`21083`.) A new policy option :attr:`EmailPolicy.utf8 ` can be set to ``True`` to encode email headers using the UTF-8 charset instead of using encoded words. This allows ``Messages`` to be formatted according to :rfc:`6532` and used with an SMTP server that supports the :rfc:`6531` ``SMTPUTF8`` extension. (Contributed by R. David Murray in :issue:`24211`.) :class:`email.mime.text.MIMEText` constructor now accepts a :class:`~email.charset.Charset` instance. (Contributed by Claude Paroz and Berker Peksag in :issue:`16324`.) enum ---- The :class:`~enum.Enum` callable has a new parameter *start* to specify the initial number of enum values if only *names* are provided:: >>> Animal = enum.Enum('Animal', 'cat dog', start=10) >>> Animal.cat >>> Animal.dog (Contributed by Ethan Furman in :issue:`21706`.) faulthandler ------------ :func:`~faulthandler.enable`, :func:`~faulthandler.register`, :func:`~faulthandler.dump_traceback` and :func:`~faulthandler.dump_traceback_later` functions now accept file descriptors in addition to file-like objects. (Contributed by Wei Wu in :issue:`23566`.) functools --------- .. _whatsnew-lrucache: Most of :func:`~functools.lru_cache` machinery is now implemented in C, making it significantly faster. (Contributed by Matt Joiner, Alexey Kachayev, and Serhiy Storchaka in :issue:`14373`.) glob ---- :func:`~glob.iglob` and :func:`~glob.glob` functions now support recursive search in subdirectories using the ``"**"`` pattern. (Contributed by Serhiy Storchaka in :issue:`13968`.) gzip ---- The *mode* argument of :class:`~gzip.GzipFile` constructor now accepts ``"x"`` to request exclusive creation. (Contributed by Tim Heaney in :issue:`19222`.) heapq ----- Element comparison in :func:`~heapq.merge` can now be customized by passing a :term:`key function` in a new optional *key* keyword argument, and a new optional *reverse* keyword argument can be used to reverse element comparison:: >>> import heapq >>> a = ['9', '777', '55555'] >>> b = ['88', '6666'] >>> list(heapq.merge(a, b, key=len)) ['9', '88', '777', '6666', '55555'] >>> list(heapq.merge(reversed(a), reversed(b), key=len, reverse=True)) ['55555', '6666', '777', '88', '9'] (Contributed by Raymond Hettinger in :issue:`13742`.) http ---- A new :class:`HTTPStatus ` enum that defines a set of HTTP status codes, reason phrases and long descriptions written in English. (Contributed by Demian Brecht in :issue:`21793`.) http.client ----------- :meth:`HTTPConnection.getresponse() ` now raises a :exc:`~http.client.RemoteDisconnected` exception when a remote server connection is closed unexpectedly. Additionally, if a :exc:`ConnectionError` (of which ``RemoteDisconnected`` is a subclass) is raised, the client socket is now closed automatically, and will reconnect on the next request:: import http.client conn = http.client.HTTPConnection('www.python.org') for retries in range(3): try: conn.request('GET', '/') resp = conn.getresponse() except http.client.RemoteDisconnected: pass (Contributed by Martin Panter in :issue:`3566`.) idlelib and IDLE ---------------- Since idlelib implements the IDLE shell and editor and is not intended for import by other programs, it gets improvements with every release. See :file:`Lib/idlelib/NEWS.txt` for a cumulative list of changes since 3.4.0, as well as changes made in future 3.5.x releases. This file is also available from the IDLE Help -> About Idle dialog. imaplib ------- The :class:`~imaplib.IMAP4` class now supports context manager protocol. When used in a :keyword:`with` statement, the IMAP4 ``LOGOUT`` command will be called automatically at the end of the block. (Contributed by Tarek Ziadé and Serhiy Storchaka in :issue:`4972`.) The :mod:`imaplib` module now supports :rfc:`5161` (ENABLE Extension) and :rfc:`6855` (UTF-8 Support) via the :meth:`IMAP4.enable ` method. A new :attr:`IMAP4.utf8_enabled ` attribute, tracks whether or not :rfc:`6855` support is enabled. (Contributed by Milan Oberkirch, R. David Murray, and Maciej Szulik in :issue:`21800`.) The :mod:`imaplib` module now automatically encodes non-ASCII string usernames and passwords using UTF-8, as recommended by the RFCs. (Contributed by Milan Oberkirch in :issue:`21800`.) imghdr ------ The :func:`~imghdr.what` function now recognizes the `OpenEXR `_ format (contributed by Martin Vignali and Claudiu Popa in :issue:`20295`), and the `WebP `_ format (contributed by Fabrice Aneche and Claudiu Popa in :issue:`20197`.) importlib --------- The :class:`util.LazyLoader ` class allows for lazy loading of modules in applications where startup time is important. (Contributed by Brett Cannon in :issue:`17621`.) The :func:`abc.InspectLoader.source_to_code ` method is now a static method. This makes it easier to initialize a module object with code compiled from a string by running ``exec(code, module.__dict__)``. (Contributed by Brett Cannon in :issue:`21156`.) The new :func:`util.module_from_spec ` function is now the preferred way to create a new module. As opposed to creating a :class:`types.ModuleType` instance directly, this new function will set the various import-controlled attributes based on the passed-in spec object. (Contributed by Brett Cannon in :issue:`20383`.) inspect ------- Both :class:`~inspect.Signature` and :class:`~inspect.Parameter` classes are now picklable and hashable. (Contributed by Yury Selivanov in :issue:`20726` and :issue:`20334`.) A new :meth:`BoundArguments.apply_defaults ` method provides a way to set default values for missing arguments:: >>> def foo(a, b='ham', *args): pass >>> ba = inspect.signature(foo).bind('spam') >>> ba.apply_defaults() >>> ba.arguments OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())]) (Contributed by Yury Selivanov in :issue:`24190`.) A new class method :meth:`Signature.from_callable ` makes subclassing of :class:`~inspect.Signature` easier. (Contributed by Yury Selivanov and Eric Snow in :issue:`17373`.) The :func:`~inspect.signature` function now accepts a ``follow_wrapped`` optional keyword argument, which, when set to ``False``, disables automatic following of ``__wrapped__`` links. (Contributed by Yury Selivanov in :issue:`20691`.) A set of new functions to inspect :term:`coroutine functions ` and :term:`coroutine objects ` has been added: :func:`~inspect.iscoroutine`, :func:`~inspect.iscoroutinefunction`, :func:`~inspect.isawaitable`, :func:`~inspect.getcoroutinelocals`, and :func:`~inspect.getcoroutinestate`. (Contributed by Yury Selivanov in :issue:`24017` and :issue:`24400`.) :func:`~inspect.stack`, :func:`~inspect.trace`, :func:`~inspect.getouterframes`, and :func:`~inspect.getinnerframes` functions now return a list of named tuples. (Contributed by Daniel Shahaf in :issue:`16808`.) io -- A new :meth:`BufferedIOBase.readinto1 ` method, that uses at most one call to the underlying raw stream's :meth:`RawIOBase.read ` (or :meth:`RawIOBase.readinto `) method. (Contributed by Nikolaus Rath in :issue:`20578`.) ipaddress --------- Both :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.IPv6Network` classes now accept an ``(address, netmask)`` tuple argument, so as to easily construct network objects from existing addresses:: >>> import ipaddress >>> ipaddress.IPv4Network(('127.0.0.0', 8)) IPv4Network('127.0.0.0/8') >>> ipaddress.IPv4Network(('127.0.0.0', '255.0.0.0')) IPv4Network('127.0.0.0/8') (Contributed by Peter Moody and Antoine Pitrou in :issue:`16531`.) A new :attr:`~ipaddress.IPv4Network.reverse_pointer>` attribute for :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.IPv6Network` classes returns the name of the reverse DNS PTR record:: >>> import ipaddress >>> addr = ipaddress.IPv4Address('127.0.0.1') >>> addr.reverse_pointer '1.0.0.127.in-addr.arpa' >>> addr6 = ipaddress.IPv6Address('::1') >>> addr6.reverse_pointer '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa' (Contributed by Leon Weber in :issue:`20480`.) json ---- The :mod:`json.tool` command line interface now preserves the order of keys in JSON objects passed in input. The new ``--sort-keys`` option can be used to sort the keys alphabetically. (Contributed by Berker Peksag in :issue:`21650`.) JSON decoder now raises :exc:`json.JSONDecodeError` instead of :exc:`ValueError` to provide better context information about the error. (Contributed by Serhiy Storchaka in :issue:`19361`.) linecache --------- A new :func:`~linecache.lazycache` function can be used to capture information about a non-file based module to permit getting its lines later via :func:`~linecache.getline`. This avoids doing I/O until a line is actually needed, without having to carry the module globals around indefinitely. (Contributed by Robert Collins in :issue:`17911`.) locale ------ A new :func:`~locale.delocalize` function can be used to convert a string into a normalized number string, taking the ``LC_NUMERIC`` settings into account:: >>> import locale >>> locale.setlocale(locale.LC_NUMERIC, 'de_DE.UTF-8') 'de_DE.UTF-8' >>> locale.delocalize('1.234,56') '1234.56' >>> locale.setlocale(locale.LC_NUMERIC, 'en_US.UTF-8') 'en_US.UTF-8' >>> locale.delocalize('1,234.56') '1234.56' (Contributed by Cédric Krier in :issue:`13918`.) logging ------- All logging methods (:class:`~logging.Logger` :meth:`~logging.Logger.log`, :meth:`~logging.Logger.exception`, :meth:`~logging.Logger.critical`, :meth:`~logging.Logger.debug`, etc.), now accept exception instances as an ``exc_info`` argument, in addition to boolean values and exception tuples:: >>> import logging >>> try: ... 1/0 ... except ZeroDivisionError as ex: ... logging.error('exception', exc_info=ex) ERROR:root:exception (Contributed by Yury Selivanov in :issue:`20537`.) The :class:`handlers.HTTPHandler ` class now accepts an optional :class:`ssl.SSLContext` instance to configure SSL settings used in an HTTP connection. (Contributed by Alex Gaynor in :issue:`22788`.) The :class:`handlers.QueueListener ` class now takes a *respect_handler_level* keyword argument which, if set to ``True``, will pass messages to handlers taking handler levels into account. (Contributed by Vinay Sajip.) lzma ---- The :meth:`LZMADecompressor.decompress ` method now accepts an optional *max_length* argument to limit the maximum size of decompressed data. (Contributed by Martin Panter in :issue:`15955`.) math ---- Two new constants have been added to the :mod:`math` module: :data:`~math.inf` and :data:`~math.nan`. (Contributed by Mark Dickinson in :issue:`23185`.) A new function :func:`~math.isclose` provides a way to test for approximate equality. (Contributed by Chris Barker and Tal Einat in :issue:`24270`.) A new :func:`~math.gcd` function has been added. The :func:`fractions.gcd` function is now deprecated. (Contributed by Mark Dickinson and Serhiy Storchaka in :issue:`22486`.) multiprocessing --------------- :func:`sharedctypes.synchronized ` objects now support the :term:`context manager` protocol. (Contributed by Charles-François Natali in :issue:`21565`.) operator -------- :func:`~operator.attrgetter`, :func:`~operator.itemgetter`, and :func:`~operator.methodcaller` objects now support pickling. (Contributed by Josh Rosenberg and Serhiy Storchaka in :issue:`22955`.) New :func:`~operator.matmul` and :func:`~operator.imatmul` functions to perform matrix multiplication. (Contributed by Benjamin Peterson in :issue:`21176`.) os -- The new :func:`~os.scandir` function returning an iterator of :class:`~os.DirEntry` objects has been added. If possible, :func:`~os.scandir` extracts file attributes while scanning a directory, removing the need to perform subsequent system calls to determine file type or attributes, which may significantly improve performance. (Contributed by Ben Hoyt with the help of Victor Stinner in :issue:`22524`.) On Windows, a new :attr:`stat_result.st_file_attributes ` attribute is now available. It corresponds to ``dwFileAttributes`` member of the ``BY_HANDLE_FILE_INFORMATION`` structure returned by ``GetFileInformationByHandle()``. (Contributed by Ben Hoyt in :issue:`21719`.) The :func:`~os.urandom` function now uses ``getrandom()`` syscall on Linux 3.17 or newer, and ``getentropy()`` on OpenBSD 5.6 and newer, removing the need to use ``/dev/urandom`` and avoiding failures due to potential file descriptor exhaustion. (Contributed by Victor Stinner in :issue:`22181`.) New :func:`~os.get_blocking` and :func:`~os.set_blocking` functions allow to get and set a file descriptor blocking mode (:data:`~os.O_NONBLOCK`.) (Contributed by Victor Stinner in :issue:`22054`.) The :func:`~os.truncate` and :func:`~os.ftruncate` functions are now supported on Windows. (Contributed by Steve Dower in :issue:`23668`.) There is a new :func:`os.path.commonpath` function returning the longest common sub-path of each passed pathname. Unlike the :func:`os.path.commonprefix` function, it always returns a valid path:: >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib']) '/usr/l' >>> os.path.commonpath(['/usr/lib', '/usr/local/lib']) '/usr' (Contributed by Rafik Draoui and Serhiy Storchaka in :issue:`10395`.) pathlib ------- The new :meth:`Path.samefile ` method can be used to check whether the path points to the same file as other path, which can be either an another :class:`~pathlib.Path` object, or a string:: >>> import pathlib >>> p1 = pathlib.Path('/etc/hosts') >>> p2 = pathlib.Path('/etc/../etc/hosts') >>> p1.samefile(p2) True (Contributed by Vajrasky Kok and Antoine Pitrou in :issue:`19775`.) The :meth:`Path.mkdir ` method how accepts a new optional ``exist_ok`` argument to match ``mkdir -p`` and :func:`os.makrdirs` functionality. (Contributed by Berker Peksag in :issue:`21539`.) There is a new :meth:`Path.expanduser ` method to expand ``~`` and ``~user`` prefixes. (Contributed by Serhiy Storchaka and Claudiu Popa in :issue:`19776`.) A new :meth:`Path.home ` class method can be used to get an instance of :class:`~pathlib.Path` object representing the user’s home directory. (Contributed by Victor Salgado and Mayank Tripathi in :issue:`19777`.) New :meth:`Path.write_text `, :meth:`Path.read_text `, :meth:`Path.write_bytes `, :meth:`Path.read_bytes ` methods to simplify read/write operations on files. The following code snippet will create or rewrite existing file ``~/spam42``:: >>> import pathlib >>> p = pathlib.Path('~/spam42') >>> p.expanduser().write_text('ham') 3 (Contributed by Christopher Welborn in :issue:`20218`.) pickle ------ Nested objects, such as unbound methods or nested classes, can now be pickled using :ref:`pickle protocols ` older than protocol version 4. Protocol version 4 already supports these cases. (Contributed by Serhiy Storchaka in :issue:`23611`.) poplib ------ A new :meth:`POP3.utf8 ` command enables :rfc:`6856` (Internationalized Email) support, if a POP server supports it. (Contributed by Milan OberKirch in :issue:`21804`.) re -- References and conditional references to groups with fixed length are now allowed in lookbehind assertions:: >>> import re >>> pat = re.compile(r'(a|b).(?<=\1)c') >>> pat.match('aac') <_sre.SRE_Match object; span=(0, 3), match='aac'> >>> pat.match('bbc') <_sre.SRE_Match object; span=(0, 3), match='bbc'> (Contributed by Serhiy Storchaka in :issue:`9179`.) The number of capturing groups in regular expression is no longer limited by 100. (Contributed by Serhiy Storchaka in :issue:`22437`.) The :func:`~re.sub` and :func:`~re.subn` functions now replace unmatched groups with empty strings instead of raising an exception. (Contributed by Serhiy Storchaka in :issue:`1519638`.) The :class:`re.error` exceptions have new attributes: :attr:`~re.error.msg`, :attr:`~re.error.pattern`, :attr:`~re.error.pos`, :attr:`~re.error.lineno`, and :attr:`~re.error.colno` that provide better context information about the error:: >>> re.compile(""" ... (?x) ... .++ ... """) Traceback (most recent call last): ... sre_constants.error: multiple repeat at position 16 (line 3, column 7) (Contributed by Serhiy Storchaka in :issue:`22578`.) readline -------- A new :func:`~readline.append_history_file` function can be used to append the specified number of trailing elements in history to the given file. (Contributed by Bruno Cauet in :issue:`22940`.) selectors --------- The new :class:`~selectors.DevpollSelector` supports efficient ``/dev/poll`` polling on Solaris. (Contributed by Giampaolo Rodola' in :issue:`18931`.) shutil ------ The :func:`~shutil.move` function now accepts a *copy_function* argument, allowing, for example, the :func:`~shutil.copy` function to be used instead of the default :func:`~shutil.copy2` if there is a need to ignore file metadata when moving. (Contributed by Claudiu Popa in :issue:`19840`.) The :func:`~shutil.make_archive` function now supports the *xztar* format. (Contributed by Serhiy Storchaka in :issue:`5411`.) signal ------ On Windows, the :func:`~signal.set_wakeup_fd` function now also supports socket handles. (Contributed by Victor Stinner in :issue:`22018`.) Various ``SIG*`` constants in the :mod:`signal` module have been converted into :mod:`Enums `. This allows meaningful names to be printed during debugging, instead of integer "magic numbers". (Contributed by Giampaolo Rodola' in :issue:`21076`.) smtpd ----- Both :class:`~smtpd.SMTPServer` and :class:`~smtpd.SMTPChannel` classes now accept a *decode_data* keyword argument to determine if the ``DATA`` portion of the SMTP transaction is decoded using the ``"utf-8"`` codec or is instead provided to the :meth:`SMTPServer.process_message ` method as a byte string. The default is ``True`` for backward compatibility reasons, but will change to ``False`` in Python 3.6. If *decode_data* is set to ``False``, the :meth:`~smtpd.SMTPServer.process_message` method must be prepared to accept keyword arguments. (Contributed by Maciej Szulik in :issue:`19662`.) The :class:`~smtpd.SMTPServer` class now advertises the ``8BITMIME`` extension (:rfc:`6152`) if *decode_data* has been set ``True``. If the client specifies ``BODY=8BITMIME`` on the ``MAIL`` command, it is passed to :meth:`SMTPServer.process_message ` via the ``mail_options`` keyword. (Contributed by Milan Oberkirch and R. David Murray in :issue:`21795`.) The :class:`~smtpd.SMTPServer` class now also supports the ``SMTPUTF8`` extension (:rfc:`6531`: Internationalized Email). If the client specified ``SMTPUTF8 BODY=8BITMIME`` on the ``MAIL`` command, they are passed to :meth:`SMTPServer.process_message ` via the ``mail_options`` keyword. It is the responsibility of the :meth:`~smtpd.SMTPServer.process_message` method to correctly handle the ``SMTPUTF8`` data. (Contributed by Milan Oberkirch in :issue:`21725`.) It is now possible to provide, directly or via name resolution, IPv6 addresses in the :class:`~smtpd.SMTPServer` constructor, and have it successfully connect. (Contributed by Milan Oberkirch in :issue:`14758`.) smtplib ------- A new :meth:`SMTP.auth ` method provides a convenient way to implement custom authentication mechanisms. (Contributed by Milan Oberkirch in :issue:`15014`.) The :meth:`SMTP.set_debuglevel ` method now accepts an additional debuglevel (2), which enables timestamps in debug messages. (Contributed by Gavin Chappell and Maciej Szulik in :issue:`16914`.) Both :meth:`SMTP.sendmail ` and :meth:`SMTP.send_message ` methods now support support :rfc:`6531` (SMTPUTF8). (Contributed by Milan Oberkirch and R. David Murray in :issue:`22027`.) sndhdr ------ :func:`~sndhdr.what` and :func:`~sndhdr.whathdr` functions now return a :func:`~collections.namedtuple`. (Contributed by Claudiu Popa in :issue:`18615`.) ssl --- .. _whatsnew-sslmemorybio: Memory BIO Support ~~~~~~~~~~~~~~~~~~ (Contributed by Geert Jansen in :issue:`21965`.) The new :class:`~ssl.SSLObject` class has been added to provide SSL protocol support for cases when the network I/O capabilities of :class:`~ssl.SSLSocket` are not necessary or suboptimal. :class:`~ssl.SSLObject` represents an SSL protocol instance, but does not implement any network I/O methods, and instead provides a memory buffer interface. The new :class:`~ssl.MemoryBIO` class can be used to pass data between Python and an SSL protocol instance. The memory BIO SSL support is primarily intended to be used in frameworks implementing asynchronous I/O for which :class:`~ssl.SSLSocket`'s readiness model ("select/poll") is inefficient. A new :meth:`SSLContext.wrap_bio ` method can be used to create a new :class:`~ssl.SSLObject` instance. Application-Layer Protocol Negotiation Support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (Contributed by Benjamin Peterson in :issue:`20188`.) Where OpenSSL support is present, :mod:`ssl` module now implements *Application-Layer Protocol Negotiation* TLS extension as described in :rfc:`7301`. The new :meth:`SSLContext.set_alpn_protocols ` can be used to specify which protocols a socket should advertise during the TLS handshake. The new :meth:`SSLSocket.selected_alpn_protocol ` returns the protocol that was selected during the TLS handshake. :data:`~ssl.HAS_ALPN` flag indicates whether APLN support is present. Other Changes ~~~~~~~~~~~~~ There is a new :meth:`SSLSocket.version ` method to query the actual protocol version in use. (Contributed by Antoine Pitrou in :issue:`20421`.) The :class:`~ssl.SSLSocket` class now implements a :meth:`SSLSocket.sendfile ` method. (Contributed by Giampaolo Rodola' in :issue:`17552`.) The :meth:`SSLSocket.send ` method now raises either :exc:`ssl.SSLWantReadError` or :exc:`ssl.SSLWantWriteError` exception on a non-blocking socket if the operation would block. Previously, it would return ``0``. (Contributed by Nikolaus Rath in :issue:`20951`.) The :func:`~ssl.cert_time_to_seconds` function now interprets the input time as UTC and not as local time, per :rfc:`5280`. Additionally, the return value is always an :class:`int`. (Contributed by Akira Li in :issue:`19940`.) New :meth:`SSLObject.shared_ciphers ` and :meth:`SSLSocket.shared_ciphers ` methods return the list of ciphers sent by the client during the handshake. (Contributed by Benjamin Peterson in :issue:`23186`.) The :meth:`SSLSocket.do_handshake `, :meth:`SSLSocket.read `, :meth:`SSLSocket.shutdown `, and :meth:`SSLSocket.write ` methods of :class:`ssl.SSLSocket` class no longer reset the socket timeout every time bytes are received or sent. The socket timeout is now the maximum total duration of the method. (Contributed by Victor Stinner in :issue:`23853`.) The :func:`~ssl.match_hostname` function now supports matching of IP addresses. (Contributed by Antoine Pitrou in :issue:`23239`.) socket ------ Functions with timeouts now use a monotonic clock, instead of a system clock. (Contributed by Victor Stinner in :issue:`22043`.) A new :meth:`socket.sendfile ` method allows to send a file over a socket by using the high-performance :func:`os.sendfile` function on UNIX resulting in uploads being from 2 to 3 times faster than when using plain :meth:`socket.send `. (Contributed by Giampaolo Rodola' in :issue:`17552`.) The :meth:`socket.sendall ` method no longer resets the socket timeout every time bytes are received or sent. The socket timeout is now the maximum total duration to send all data. (Contributed by Victor Stinner in :issue:`23853`.) The *backlog* argument of the :meth:`socket.listen ` method is now optional. By default it is set to :data:`SOMAXCONN ` or to ``128`` whichever is less. (Contributed by Charles-François Natali in :issue:`21455`.) sqlite3 ------- The :class:`~sqlite3.Row` class now fully supports sequence protocol, in particular :func:`reversed` iteration and slice indexing. (Contributed by Claudiu Popa in :issue:`10203`; by Lucas Sinclair, Jessica McKellar, and Serhiy Storchaka in :issue:`13583`.) .. _whatsnew-subprocess: subprocess ---------- The new :func:`~subprocess.run` function has been added. It runs the specified command and and returns a :class:`~subprocess.CompletedProcess` object, which describes a finished process. The new API is more consistent and is the recommended approach to invoking subprocesses in Python code that does not need to maintain compatibility with earlier Python versions. (Contributed by Thomas Kluyver in :issue:`23342`.) Examples:: >>> subprocess.run(["ls", "-l"]) # doesn't capture output CompletedProcess(args=['ls', '-l'], returncode=0) >>> subprocess.run("exit 1", shell=True, check=True) Traceback (most recent call last): ... subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 >>> subprocess.run(["ls", "-l", "/dev/null"], stdout=subprocess.PIPE) CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0, stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n') sys --- A new :func:`~sys.set_coroutine_wrapper` function allows setting a global hook that will be called whenever a :term:`coroutine object ` is created by an :keyword:`async def` function. A corresponding :func:`~sys.get_coroutine_wrapper` can be used to obtain a currently set wrapper. Both functions are :term:`provisional `, and are intended for debugging purposes only. (Contributed by Yury Selivanov in :issue:`24017`.) A new :func:`~sys.is_finalizing` function can be used to check if the Python interpreter is :term:`shutting down `. (Contributed by Antoine Pitrou in :issue:`22696`.) sysconfig --------- The name of the user scripts directory on Windows now includes the first two components of Python version. (Contributed by Paul Moore in :issue:`23437`.) tarfile ------- The *mode* argument of the :func:`~tarfile.open` function now accepts ``"x"`` to request exclusive creation. (Contributed by Berker Peksag in :issue:`21717`.) :meth:`TarFile.extractall ` and :meth:`TarFile.extract ` methods now take a keyword argument *numeric_only*. If set to ``True``, the extracted files and directories will be owned by the numeric ``uid`` and ``gid`` from the tarfile. If set to ``False`` (the default, and the behavior in versions prior to 3.5), they will be owned by the named user and group in the tarfile. (Contributed by Michael Vogt and Eric Smith in :issue:`23193`.) The :meth:`TarFile.list ` now accepts an optional *members* keyword argument that can be set to a subset of the list returned by :meth:`TarFile.getmembers `. (Contributed by Serhiy Storchaka in :issue:`21549`.) threading --------- Both :meth:`Lock.acquire ` and :meth:`RLock.acquire ` methods now use a monotonic clock for timeout management. (Contributed by Victor Stinner in :issue:`22043`.) time ---- The :func:`~time.monotonic` function is now always available. (Contributed by Victor Stinner in :issue:`22043`.) timeit ------ A new command line option ``-u`` or ``--unit=U`` can be used to specify the time unit for the timer output. Supported options are ``usec``, ``msec``, or ``sec``. (Contributed by Julian Gindi in :issue:`18983`.) The :func:`~timeit.timeit` function has a new *globals* parameter for specifying the namespace in which the code will be running. (Contributed by Ben Roberts in :issue:`2527`.) tkinter ------- The :mod:`tkinter._fix` module used for setting up the Tcl/Tk environment on Windows has been replaced by a private function in the :mod:`_tkinter` module which makes no permanent changes to environment variables. (Contributed by Zachary Ware in :issue:`20035`.) .. _whatsnew-traceback: traceback --------- New :func:`~traceback.walk_stack` and :func:`~traceback.walk_tb` functions to conveniently traverse frame and traceback objects. (Contributed by Robert Collins in :issue:`17911`.) New lightweight classes: :class:`~traceback.TracebackException`, :class:`~traceback.StackSummary`, and :class:`traceback.FrameSummary`. (Contributed by Robert Collins in :issue:`17911`.) Both :func:`~traceback.print_tb` and :func:`~traceback.print_stack` functions now support negative values for the *limit* argument. (Contributed by Dmitry Kazakov in :issue:`22619`.) types ----- A new :func:`~types.coroutine` function to transform :term:`generator ` and :class:`generator-like ` objects into :term:`awaitables `. (Contributed by Yury Selivanov in :issue:`24017`.) A new :class:`~types.CoroutineType` is the type of :term:`coroutine` objects created by :keyword:`async def` functions. (Contributed by Yury Selivanov in :issue:`24400`.) urllib ------ A new :class:`request.HTTPPasswordMgrWithPriorAuth ` class allows HTTP Basic Authentication credentials to be managed so as to eliminate unnecessary ``401`` response handling, or to unconditionally send credentials on the first request in order to communicate with servers that return a ``404`` response instead of a ``401`` if the ``Authorization`` header is not sent. (Contributed by Matej Cepl in :issue:`19494` and Akshit Khurana in :issue:`7159`.) A new *quote_via* argument for the :func:`parse.urlencode ` function provides a way to control the encoding of query parts if needed. (Contributed by Samwyse and Arnon Yaari in :issue:`13866`.) The :func:`request.urlopen ` function accepts an :class:`ssl.SSLContext` object as a *context* argument, which will be used for the HTTPS connection. (Contributed by Alex Gaynor in :issue:`22366`.) The :func:`parse.urljoin ` was updated to use the :rfc:`3986` semantics for the resolution of relative URLs, rather than :rfc:`1808` and :rfc:`2396`. (Contributed by Demian Brecht and Senthil Kumaran in :issue:`22118`.) unicodedata ----------- The :mod:`unicodedata` module now uses data from `Unicode 8.0.0 `_. unittest -------- The :meth:`TestLoader.loadTestsFromModule ` method now accepts a keyword-only argument *pattern* which is passed to ``load_tests`` as the third argument. Found packages are now checked for ``load_tests`` regardless of whether their path matches *pattern*, because it is impossible for a package name to match the default pattern. (Contributed by Robert Collins and Barry A. Warsaw in :issue:`16662`.) Unittest discovery errors now are exposed in :data:`TestLoader.errors ` attribute of the :class:`~unittest.TestLoader` instance. (Contributed by Robert Collins in :issue:`19746`.) A new command line option ``--locals`` to show local variables in tracebacks. (Contributed by Robert Collins in :issue:`22936`.) unittest.mock ------------- The :class:`~unittest.mock.Mock` has the following improvements: * Class constructor has a new *unsafe* parameter, which causes mock objects to raise :exc:`AttributeError` on attribute names starting with ``"assert"``. (Contributed by Kushal Das in :issue:`21238`.) * A new :meth:`Mock.assert_not_called ` method to check if the mock object was called. (Contributed by Kushal Das in :issue:`21262`.) The :class:`~unittest.mock.MagicMock` class now supports :meth:`__truediv__`, :meth:`__divmod__` and :meth:`__matmul__` operators. (Contributed by Johannes Baiter in :issue:`20968`, and Håkan Lövdahl in :issue:`23581` and :issue:`23568`.) It is no longer necessary to explicitly pass ``create=True`` to the :func:`~unittest.mock.patch` function when patching builtin names. (Contributed by Kushal Das in :issue:`17660`.) wsgiref ------- The *headers* argument of the :class:`headers.Headers ` class constructor is now optional. (Contributed by Pablo Torres Navarrete and SilentGhost in :issue:`5800`.) xmlrpc ------ The :class:`client.ServerProxy ` class is now a :term:`context manager`. (Contributed by Claudiu Popa in :issue:`20627`.) :class:`client.ServerProxy ` constructor now accepts an optional :class:`ssl.SSLContext` instance. (Contributed by Alex Gaynor in :issue:`22960`.) xml.sax ------- SAX parsers now support a character stream of the :class:`xmlreader.InputSource ` object. (Contributed by Serhiy Storchaka in :issue:`2175`.) :func:`~xml.sax.parseString` now accepts a :class:`str` instance. (Contributed by Serhiy Storchaka in :issue:`10590`.) zipfile ------- ZIP output can now be written to unseekable streams. (Contributed by Serhiy Storchaka in :issue:`23252`.) The *mode* argument of :meth:`ZipFile.open ` method now accepts ``"x"`` to request exclusive creation. (Contributed by Serhiy Storchaka in :issue:`21717`.) Other module-level changes ========================== Many functions in :mod:`mmap`, :mod:`ossaudiodev`, :mod:`socket`, :mod:`ssl`, and :mod:`codecs` modules now accept writable :term:`bytes-like objects `. (Contributed by Serhiy Storchaka in :issue:`23001`.) Optimizations ============= The :func:`os.walk` function has been sped up by 3 to 5 times on POSIX systems, and by 7 to 20 times on Windows. This was done using the new :func:`os.scandir` function, which exposes file information from the underlying ``readdir`` or ``FindFirstFile``/``FindNextFile`` system calls. (Contributed by Ben Hoyt with help from Victor Stinner in :issue:`23605`.) Construction of ``bytes(int)`` (filled by zero bytes) is faster and uses less memory for large objects. ``calloc()`` is used instead of ``malloc()`` to allocate memory for these objects. (Contributed by Victor Stinner in :issue:`21233`.) Some operations on :mod:`ipaddress` :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.IPv6Network` have been massively sped up, such as :meth:`~ipaddress.IPv4Network.subnets`, :meth:`~ipaddress.IPv4Network.supernet`, :func:`~ipaddress.summarize_address_range`, :func:`~ipaddress.collapse_addresses`. The speed up can range from 3 to 15 times. (Contributed by Antoine Pitrou, Michel Albert, and Markus in :issue:`21486`, :issue:`21487`, :issue:`20826`, :issue:`23266`.) Pickling of :mod:`ipaddress` objects was optimized to produce significantly smaller output. (Contributed by Serhiy Storchaka in :issue:`23133`.) Many operations on :class:`io.BytesIO` are now 50% to 100% faster. (Contributed by Serhiy Storchaka in :issue:`15381` and David Wilson in :issue:`22003`.) The :func:`marshal.dumps` function is now faster: 65-85% with versions 3 and 4, 20-25% with versions 0 to 2 on typical data, and up to 5 times in best cases. (Contributed by Serhiy Storchaka in :issue:`20416` and :issue:`23344`.) The UTF-32 encoder is now 3 to 7 times faster. (Contributed by Serhiy Storchaka in :issue:`15027`.) Regular expressions are now parsed up to 10% faster. (Contributed by Serhiy Storchaka in :issue:`19380`.) The :func:`json.dumps` function was optimized to run with ``ensure_ascii=False`` as fast as with ``ensure_ascii=True``. (Contributed by Naoki Inada in :issue:`23206`.) The :c:func:`PyObject_IsInstance` and :c:func:`PyObject_IsSubclass` functions have been sped up in the common case that the second argument has :class:`type` as its metaclass. (Contributed Georg Brandl by in :issue:`22540`.) Method caching was slightly improved, yielding up to 5% performance improvement in some benchmarks. (Contributed by Antoine Pitrou in :issue:`22847`.) Objects from :mod:`random` module now use two times less memory on 64-bit builds. (Contributed by Serhiy Storchaka in :issue:`23488`.) The :func:`property` getter calls are up to 25% faster. (Contributed by Joe Jevnik in :issue:`23910`.) Instantiation of :class:`fractions.Fraction` is now up to 30% faster. (Contributed by Stefan Behnel in :issue:`22464`.) String methods :meth:`~str.find`, :meth:`~str.rfind`, :meth:`~str.split`, :meth:`~str.partition` and :keyword:`in` string operator are now significantly faster for searching 1-character substrings. (Contributed by Serhiy Storchaka in :issue:`23573`.) Build and C API Changes ======================= New ``calloc`` functions were added: * :c:func:`PyMem_RawCalloc`, * :c:func:`PyMem_Calloc`, * :c:func:`PyObject_Calloc`, * :c:func:`_PyObject_GC_Calloc`. (Contributed by Victor Stinner in :issue:`21233`.) New encoding/decoding helper functions: * :c:func:`Py_DecodeLocale` (replaced ``_Py_char2wchar()``), * :c:func:`Py_EncodeLocale` (replaced ``_Py_wchar2char()``). (Contributed by Victor Stinner in :issue:`18395`.) A new :c:func:`PyCodec_NameReplaceErrors` function to replace the unicode encode error with ``\N{...}`` escapes. (Contributed by Serhiy Storchaka in :issue:`19676`.) A new :c:func:`PyErr_FormatV` function similar to :c:func:`PyErr_Format`, but accepts a ``va_list`` argument. (Contributed by Antoine Pitrou in :issue:`18711`.) A new :c:data:`PyExc_RecursionError` exception. (Contributed by Georg Brandl in :issue:`19235`.) New :c:func:`PyModule_FromDefAndSpec`, :c:func:`PyModule_FromDefAndSpec2`, and :c:func:`PyModule_ExecDef` introduced by :pep:`489` -- multi-phase extension module initialization. (Contributed by Petr Viktorin in :issue:`24268`.) New :c:func:`PyNumber_MatrixMultiply` and :c:func:`PyNumber_InPlaceMatrixMultiply` functions to perform matrix multiplication. (Contributed by Benjamin Peterson in :issue:`21176`. See also :pep:`465` for details.) The :c:member:`PyTypeObject.tp_finalize` slot is now part of stable ABI. Windows builds now require Microsoft Visual C++ 14.0, which is available as part of `Visual Studio 2015 `_. Extension modules now include platform information tag in their filename on some platforms (the tag is optional, and CPython will import extensions without it; although if the tag is present and mismatched, the extension won't be loaded): * On Linux, extension module filenames end with ``.cpython-m--.pyd``: * ```` is the major number of the Python version; for Python 3.5 this is ``3``. * ```` is the minor number of the Python version; for Python 3.5 this is ``5``. * ```` is the hardware architecture the extension module was built to run on. It's most commonly either ``i386`` for 32-bit Intel platforms or ``x86_64`` for 64-bit Intel (and AMD) platforms. * ```` is always ``linux-gnu``, except for extensions built to talk to the 32-bit ABI on 64-bit platforms, in which case it is ``linux-gnu32`` (and ```` will be ``x86_64``). * On Windows, extension module filenames end with ``.cp-.pyd``: * ```` is the major number of the Python version; for Python 3.5 this is ``3``. * ```` is the minor number of the Python version; for Python 3.5 this is ``5``. * ```` is the platform the extension module was built for, either ``win32`` for Win32, ``win_amd64`` for Win64, ``win_ia64`` for Windows Itanium 64, and ``win_arm`` for Windows on ARM. * If built in debug mode, ```` will be ``_d``, otherwise it will be blank. * On OS X platforms, extension module filenames now end with ``-darwin.so``. * On all other platforms, extension module filenames are the same as they were with Python 3.4. Deprecated ========== New Keywords ------------ ``async`` and ``await`` are not recommended to be used as variable, class, function or module names. Introduced by :pep:`492` in Python 3.5, they will become proper keywords in Python 3.7. Deprecated Python Behavior -------------------------- Raising :exc:`StopIteration` inside a generator will now generate a silent :exc:`PendingDeprecationWarning`, which will become a non-silent deprecation warning in Python 3.6 and will trigger a :exc:`RuntimeError` in Python 3.7. See :ref:`PEP 479: Change StopIteration handling inside generators ` for details. Unsupported Operating Systems ----------------------------- Windows XP is no longer supported by Microsoft, thus, per :PEP:`11`, CPython 3.5 is no longer officially supported on this OS. Deprecated Python modules, functions and methods ------------------------------------------------ The :mod:`formatter` module has now graduated to full deprecation and is still slated for removal in Python 3.6. The :func:`asyncio.async` function is deprecated in favor of :func:`~asyncio.ensure_future`. The :mod:`smtpd` module has in the past always decoded the DATA portion of email messages using the ``utf-8`` codec. This can now be controlled by the new *decode_data* keyword to :class:`~smtpd.SMTPServer`. The default value is ``True``, but this default is deprecated. Specify the *decode_data* keyword with an appropriate value to avoid the deprecation warning. Directly assigning values to the :attr:`~http.cookies.Morsel.key`, :attr:`~http.cookies.Morsel.value` and :attr:`~http.cookies.Morsel.coded_value` of :class:`~http.cookies.Morsel` objects is deprecated. Use the :func:`~http.cookies.Morsel.set` method instead. In addition, the undocumented *LegalChars* parameter of :func:`~http.cookies.Morsel.set` is deprecated, and is now ignored. Passing a format string as keyword argument *format_string* to the :meth:`~string.Formatter.format` method of the :class:`string.Formatter` class has been deprecated. (Contributed by Serhiy Storchaka in :issue:`23671`.) The :func:`platform.dist` and :func:`platform.linux_distribution` functions are now deprecated and will be removed in Python 3.7. Linux distributions use too many different ways of describing themselves, so the functionality is left to a package. (Contributed by Vajrasky Kok and Berker Peksag in :issue:`1322`.) The previously undocumented ``from_function`` and ``from_builtin`` methods of :class:`inspect.Signature` are deprecated. Use new :meth:`inspect.Signature.from_callable` instead. (Contributed by Yury Selivanov in :issue:`24248`.) The :func:`inspect.getargspec` function is deprecated and scheduled to be removed in Python 3.6. (See :issue:`20438` for details.) The :mod:`inspect` :func:`~inspect.getfullargspec`, :func:`~inspect.getargvalues`, :func:`~inspect.getcallargs`, :func:`~inspect.getargvalues`, :func:`~inspect.formatargspec`, and :func:`~inspect.formatargvalues` functions are deprecated in favor of :func:`inspect.signature` API. (Contributed by Yury Selivanov in :issue:`20438`.) Use of ``re.LOCALE`` flag with str patterns or ``re.ASCII`` is now deprecated. (Contributed by Serhiy Storchaka in :issue:`22407`.) Use of unrecognized special sequences consisting of ``'\'`` and an ASCII letter in regular expression patterns and replacement patterns now raises a deprecation warning and will be forbidden in Python 3.6. (Contributed by Serhiy Storchaka in :issue:`23622`.) The undocumented and unofficial *use_load_tests* default argument of the :meth:`unittest.TestLoader.loadTestsFromModule` method now is deprecated and ignored. (Contributed by Robert Collins and Barry A. Warsaw in :issue:`16662`.) Removed ======= API and Feature Removals ------------------------ The following obsolete and previously deprecated APIs and features have been removed: * The ``__version__`` attribute has been dropped from the email package. The email code hasn't been shipped separately from the stdlib for a long time, and the ``__version__`` string was not updated in the last few releases. * The internal ``Netrc`` class in the :mod:`ftplib` module was deprecated in 3.4, and has now been removed. (Contributed by Matt Chaput in :issue:`6623`.) * The concept of ``.pyo`` files has been removed. * The JoinableQueue class in the provisional :mod:`asyncio` module was deprecated in 3.4.4 and is now removed. (Contributed by A. Jesse Jiryu Davis in :issue:`23464`.) Porting to Python 3.5 ===================== This section lists previously described changes and other bugfixes that may require changes to your code. Changes in Python behavior -------------------------- * Due to an oversight, earlier Python versions erroneously accepted the following syntax:: f(1 for x in [1], *args) f(1 for x in [1], **kwargs) Python 3.5 now correctly raises a :exc:`SyntaxError`, as generator expressions must be put in parentheses if not a sole argument to a function. Changes in the Python API ------------------------- * :pep:`475`: System calls are now retried when interrupted by a signal instead of raising :exc:`InterruptedError` if the Python signal handler does not raise an exception. * Before Python 3.5, a :class:`datetime.time` object was considered to be false if it represented midnight in UTC. This behavior was considered obscure and error-prone and has been removed in Python 3.5. See :issue:`13936` for full details. * The :meth:`ssl.SSLSocket.send()` method now raises either :exc:`ssl.SSLWantReadError` or :exc:`ssl.SSLWantWriteError` on a non-blocking socket if the operation would block. Previously, it would return ``0``. (Contributed by Nikolaus Rath in :issue:`20951`.) * The ``__name__`` attribute of generator is now set from the function name, instead of being set from the code name. Use ``gen.gi_code.co_name`` to retrieve the code name. Generators also have a new ``__qualname__`` attribute, the qualified name, which is now used for the representation of a generator (``repr(gen)``). (Contributed by Victor Stinner in :issue:`21205`.) * The deprecated "strict" mode and argument of :class:`~html.parser.HTMLParser`, :meth:`HTMLParser.error`, and the :exc:`HTMLParserError` exception have been removed. (Contributed by Ezio Melotti in :issue:`15114`.) The *convert_charrefs* argument of :class:`~html.parser.HTMLParser` is now ``True`` by default. (Contributed by Berker Peksag in :issue:`21047`.) * Although it is not formally part of the API, it is worth noting for porting purposes (ie: fixing tests) that error messages that were previously of the form "'sometype' does not support the buffer protocol" are now of the form "a :term:`bytes-like object` is required, not 'sometype'". (Contributed by Ezio Melotti in :issue:`16518`.) * If the current directory is set to a directory that no longer exists then :exc:`FileNotFoundError` will no longer be raised and instead :meth:`~importlib.machinery.FileFinder.find_spec` will return ``None`` **without** caching ``None`` in :data:`sys.path_importer_cache` which is different than the typical case (:issue:`22834`). * HTTP status code and messages from :mod:`http.client` and :mod:`http.server` were refactored into a common :class:`~http.HTTPStatus` enum. The values in :mod:`http.client` and :mod:`http.server` remain available for backwards compatibility. (Contributed by Demian Brecht in :issue:`21793`.) * When an import loader defines :meth:`~importlib.machinery.Loader.exec_module` it is now expected to also define :meth:`~importlib.machinery.Loader.create_module` (raises a :exc:`DeprecationWarning` now, will be an error in Python 3.6). If the loader inherits from :class:`importlib.abc.Loader` then there is nothing to do, else simply define :meth:`~importlib.machinery.Loader.create_module` to return ``None``. (Contributed by Brett Cannon in :issue:`23014`.) * The :func:`re.split` function always ignored empty pattern matches, so the ``"x*"`` pattern worked the same as ``"x+"``, and the ``"\b"`` pattern never worked. Now :func:`re.split` raises a warning if the pattern could match an empty string. For compatibility use patterns that never match an empty string (e.g. ``"x+"`` instead of ``"x*"``). Patterns that could only match an empty string (such as ``"\b"``) now raise an error. (Contributed by Serhiy Storchaka in :issue:`22818`.) * The :class:`~http.cookies.Morsel` dict-like interface has been made self consistent: morsel comparison now takes the :attr:`~http.cookies.Morsel.key` and :attr:`~http.cookies.Morsel.value` into account, :meth:`~http.cookies.Morsel.copy` now results in a :class:`~http.cookies.Morsel` instance rather than a :class:`dict`, and :meth:`~http.cookies.Morsel.update` will now raise an exception if any of the keys in the update dictionary are invalid. In addition, the undocumented *LegalChars* parameter of :func:`~http.cookies.Morsel.set` is deprecated and is now ignored. (Contributed by Demian Brecht in :issue:`2211`.) * :pep:`488` has removed ``.pyo`` files from Python and introduced the optional ``opt-`` tag in ``.pyc`` file names. The :func:`importlib.util.cache_from_source` has gained an *optimization* parameter to help control the ``opt-`` tag. Because of this, the *debug_override* parameter of the function is now deprecated. `.pyo` files are also no longer supported as a file argument to the Python interpreter and thus serve no purpose when distributed on their own (i.e. sourcless code distribution). Due to the fact that the magic number for bytecode has changed in Python 3.5, all old `.pyo` files from previous versions of Python are invalid regardless of this PEP. * The :mod:`socket` module now exports the :data:`~socket.CAN_RAW_FD_FRAMES` constant on linux 3.6 and greater. * The :func:`~ssl.cert_time_to_seconds` function now interprets the input time as UTC and not as local time, per :rfc:`5280`. Additionally, the return value is always an :class:`int`. (Contributed by Akira Li in :issue:`19940`.) * The ``pygettext.py`` Tool now uses the standard +NNNN format for timezones in the POT-Creation-Date header. * The :mod:`smtplib` module now uses :data:`sys.stderr` instead of previous module level :data:`stderr` variable for debug output. If your (test) program depends on patching the module level variable to capture the debug output, you will need to update it to capture sys.stderr instead. * The :meth:`str.startswith` and :meth:`str.endswith` methods no longer return ``True`` when finding the empty string and the indexes are completely out of range. (Contributed by Serhiy Storchaka in :issue:`24284`.) * The :func:`inspect.getdoc` function now returns documentation strings inherited from base classes. Documentation strings no longer need to be duplicated if the inherited documentation is appropriate. To suppress an inherited string, an empty string must be specified (or the documentation may be filled in). This change affects the output of the :mod:`pydoc` module and the :func:`help` function. (Contributed by Serhiy Storchaka in :issue:`15582`.) Changes in the C API -------------------- * The undocumented :c:member:`~PyMemoryViewObject.format` member of the (non-public) :c:type:`PyMemoryViewObject` structure has been removed. All extensions relying on the relevant parts in ``memoryobject.h`` must be rebuilt. * The :c:type:`PyMemAllocator` structure was renamed to :c:type:`PyMemAllocatorEx` and a new ``calloc`` field was added. * Removed non-documented macro :c:macro:`PyObject_REPR` which leaked references. Use format character ``%R`` in :c:func:`PyUnicode_FromFormat`-like functions to format the :func:`repr` of the object. (Contributed by Serhiy Storchaka in :issue:`22453`.) * Because the lack of the :attr:`__module__` attribute breaks pickling and introspection, a deprecation warning now is raised for builtin type without the :attr:`__module__` attribute. Would be an AttributeError in future. (Contributed by Serhiy Storchaka in :issue:`20204`.) * As part of :pep:`492` implementation, ``tp_reserved`` slot of :c:type:`PyTypeObject` was replaced with a :c:member:`tp_as_async` slot. Refer to :ref:`coro-objects` for new types, structures and functions.