kbe/src/lib/python/Doc/whatsnew/3.6.rst
What's New In Python 3.6
:Editors: Elvis Pranskevichus [email protected], Yury Selivanov [email protected]
.. 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 3.6, compared to 3.5.
Python 3.6 was released on December 23, 2016. See the
changelog <https://docs.python.org/3.6/whatsnew/changelog.html>_ for a full
list of changes.
.. seealso::
:pep:`494` - Python 3.6 Release Schedule
New syntax features:
:ref:PEP 498 <whatsnew36-pep498>, formatted string literals.
:ref:PEP 515 <whatsnew36-pep515>, underscores in numeric literals.
:ref:PEP 526 <whatsnew36-pep526>, syntax for variable annotations.
:ref:PEP 525 <whatsnew36-pep525>, asynchronous generators.
:ref:PEP 530 <whatsnew36-pep530>: asynchronous comprehensions.
New library modules:
secrets: :ref:PEP 506 -- Adding A Secrets Module To The Standard Library <whatsnew36-pep506>.CPython implementation improvements:
The :ref:dict <typesmapping> type has been reimplemented to use
a :ref:more compact representation <whatsnew36-compactdict>
based on a proposal by Raymond Hettinger <https://mail.python.org/pipermail/python-dev/2012-December/123028.html>_
and similar to the PyPy dict implementation_. This resulted in dictionaries
using 20% to 25% less memory when compared to Python 3.5.
Customization of class creation has been simplified with the
:ref:new protocol <whatsnew36-pep487>.
The class attribute definition order is
:ref:now preserved <whatsnew36-pep520>.
The order of elements in **kwargs now
:ref:corresponds to the order <whatsnew36-pep468> in which keyword
arguments were passed to the function.
DTrace and SystemTap :ref:probing support <whatsnew36-tracing> has
been added.
The new :ref:PYTHONMALLOC <whatsnew36-pythonmalloc> environment variable
can now be used to debug the interpreter memory allocation and access
errors.
Significant improvements in the standard library:
The :mod:asyncio module has received new features, significant
usability and performance improvements, and a fair amount of bug fixes.
Starting with Python 3.6 the asyncio module is no longer provisional
and its API is considered stable.
A new :ref:file system path protocol <whatsnew36-pep519> has been
implemented to support :term:path-like objects <path-like object>.
All standard library functions operating on paths have been updated to
work with the new protocol.
The :mod:datetime module has gained support for
:ref:Local Time Disambiguation <whatsnew36-pep495>.
The :mod:typing module received a number of
:ref:improvements <whatsnew36-typing>.
The :mod:tracemalloc module has been significantly reworked
and is now used to provide better output for :exc:ResourceWarning
as well as provide better diagnostics for memory allocation errors.
See the :ref:PYTHONMALLOC section <whatsnew36-pythonmalloc> for more
information.
Security improvements:
The new :mod:secrets module has been added to simplify the generation of
cryptographically strong pseudo-random numbers suitable for
managing secrets such as account authentication, tokens, and similar.
On Linux, :func:os.urandom now blocks until the system urandom entropy
pool is initialized to increase the security. See the :pep:524 for the
rationale.
The :mod:hashlib and :mod:ssl modules now support OpenSSL 1.1.0.
The default settings and feature set of the :mod:ssl module have been
improved.
The :mod:hashlib module received support for the BLAKE2, SHA-3 and SHAKE
hash algorithms and the :func:~hashlib.scrypt key derivation function.
Windows improvements:
:ref:PEP 528 <whatsnew36-pep528> and :ref:PEP 529 <whatsnew36-pep529>,
Windows filesystem and console encoding changed to UTF-8.
The py.exe launcher, when used interactively, no longer prefers
Python 2 over Python 3 when the user doesn't specify a version (via
command line arguments or a config file). Handling of shebang lines
remains unchanged - "python" refers to Python 2 in that case.
python.exe and pythonw.exe have been marked as long-path aware,
which means that the 260 character path limit may no longer apply.
See :ref:removing the MAX_PATH limitation <max-path> for details.
A ._pth file can be added to force isolated mode and fully specify
all search paths to avoid registry and environment lookup. See
:ref:the documentation <finding_modules> for more information.
A python36.zip file now works as a landmark to infer
:envvar:PYTHONHOME. See :ref:the documentation <finding_modules> for
more information.
.. _PyPy dict implementation: https://morepypy.blogspot.com/2015/01/faster-more-memory-efficient-and-more.html
.. _whatsnew36-pep498:
:pep:498 introduces a new kind of string literals: f-strings, or
:ref:formatted string literals <f-strings>.
Formatted string literals are prefixed with 'f' and are similar to
the format strings accepted by :meth:str.format. They contain replacement
fields surrounded by curly braces. The replacement fields are expressions,
which are evaluated at run time, and then formatted using the
:func:format protocol::
>>> name = "Fred"
>>> f"He said his name is {name}."
'He said his name is Fred.'
>>> width = 10
>>> precision = 4
>>> value = decimal.Decimal("12.34567")
>>> f"result: {value:{width}.{precision}}" # nested fields
'result: 12.35'
.. seealso::
:pep:`498` -- Literal String Interpolation.
PEP written and implemented by Eric V. Smith.
:ref:`Feature documentation <f-strings>`.
.. _whatsnew36-pep526:
:pep:484 introduced the standard for type annotations of function
parameters, a.k.a. type hints. This PEP adds syntax to Python for annotating
the types of variables including class variables and instance variables::
primes: List[int] = []
captain: str # Note: no initial value!
class Starship:
stats: Dict[str, int] = {}
Just as for function annotations, the Python interpreter does not attach any
particular meaning to variable annotations and only stores them in the
__annotations__ attribute of a class or module.
In contrast to variable declarations in statically typed languages,
the goal of annotation syntax is to provide an easy way to specify structured
type metadata for third party tools and libraries via the abstract syntax tree
and the __annotations__ attribute.
.. seealso::
:pep:526 -- Syntax for variable annotations.
PEP written by Ryan Gonzalez, Philip House, Ivan Levkivskyi, Lisa Roach,
and Guido van Rossum. Implemented by Ivan Levkivskyi.
Tools that use or will use the new syntax:
mypy <http://www.mypy-lang.org/>,
pytype <https://github.com/google/pytype>, PyCharm, etc.
.. _whatsnew36-pep515:
:pep:515 adds the ability to use underscores in numeric literals for
improved readability. For example::
>>> 1_000_000_000_000_000
1000000000000000
>>> 0x_FF_FF_FF_FF
4294967295
Single underscores are allowed between digits and after any base specifier. Leading, trailing, or multiple underscores in a row are not allowed.
The :ref:string formatting <formatspec> language also now has support
for the '_' option to signal the use of an underscore for a thousands
separator for floating point presentation types and for integer
presentation type 'd'. For integer presentation types 'b',
'o', 'x', and 'X', underscores will be inserted every 4
digits::
>>> '{:_}'.format(1000000)
'1_000_000'
>>> '{:_x}'.format(0xFFFFFFFF)
'ffff_ffff'
.. seealso::
:pep:515 -- Underscores in Numeric Literals
PEP written by Georg Brandl and Serhiy Storchaka.
.. _whatsnew36-pep525:
:pep:492 introduced support for native coroutines and async / await
syntax to Python 3.5. A notable limitation of the Python 3.5 implementation
is that it was not possible to use await and yield in the same
function body. In Python 3.6 this restriction has been lifted, making it
possible to define asynchronous generators::
async def ticker(delay, to):
"""Yield numbers from 0 to *to* every *delay* seconds."""
for i in range(to):
yield i
await asyncio.sleep(delay)
The new syntax allows for faster and more concise code.
.. seealso::
:pep:525 -- Asynchronous Generators
PEP written and implemented by Yury Selivanov.
.. _whatsnew36-pep530:
:pep:530 adds support for using async for in list, set, dict
comprehensions and generator expressions::
result = [i async for i in aiter() if i % 2]
Additionally, await expressions are supported in all kinds
of comprehensions::
result = [await fun() for fun in funcs if await condition()]
.. seealso::
:pep:530 -- Asynchronous Comprehensions
PEP written and implemented by Yury Selivanov.
.. _whatsnew36-pep487:
It is now possible to customize subclass creation without using a metaclass.
The new __init_subclass__ classmethod will be called on the base class
whenever a new subclass is created::
class PluginBase:
subclasses = []
def __init_subclass__(cls, **kwargs):
super().__init_subclass__(**kwargs)
cls.subclasses.append(cls)
class Plugin1(PluginBase):
pass
class Plugin2(PluginBase):
pass
In order to allow zero-argument :func:super calls to work correctly from
:meth:~object.__init_subclass__ implementations, custom metaclasses must
ensure that the new __classcell__ namespace entry is propagated to
type.__new__ (as described in :ref:class-object-creation).
.. seealso::
:pep:487 -- Simpler customization of class creation
PEP written and implemented by Martin Teichmann.
:ref:Feature documentation <class-customization>
.. _whatsnew36-pep487-descriptors:
:pep:487 extends the descriptor protocol to include the new optional
:meth:~object.__set_name__ method. Whenever a new class is defined, the new
method will be called on all descriptors included in the definition, providing
them with a reference to the class being defined and the name given to the
descriptor within the class namespace. In other words, instances of
descriptors can now know the attribute name of the descriptor in the
owner class::
class IntField:
def __get__(self, instance, owner):
return instance.__dict__[self.name]
def __set__(self, instance, value):
if not isinstance(value, int):
raise ValueError(f'expecting integer in {self.name}')
instance.__dict__[self.name] = value
# this is the new initializer:
def __set_name__(self, owner, name):
self.name = name
class Model:
int_field = IntField()
.. seealso::
:pep:`487` -- Simpler customization of class creation
PEP written and implemented by Martin Teichmann.
:ref:`Feature documentation <descriptors>`
.. _whatsnew36-pep519:
File system paths have historically been represented as :class:str
or :class:bytes objects. This has led to people who write code which
operate on file system paths to assume that such objects are only one
of those two types (an :class:int representing a file descriptor
does not count as that is not a file path). Unfortunately that
assumption prevents alternative object representations of file system
paths like :mod:pathlib from working with pre-existing code,
including Python's standard library.
To fix this situation, a new interface represented by
:class:os.PathLike has been defined. By implementing the
:meth:~os.PathLike.__fspath__ method, an object signals that it
represents a path. An object can then provide a low-level
representation of a file system path as a :class:str or
:class:bytes object. This means an object is considered
:term:path-like <path-like object> if it implements
:class:os.PathLike or is a :class:str or :class:bytes object
which represents a file system path. Code can use :func:os.fspath,
:func:os.fsdecode, or :func:os.fsencode to explicitly get a
:class:str and/or :class:bytes representation of a path-like
object.
The built-in :func:open function has been updated to accept
:class:os.PathLike objects, as have all relevant functions in the
:mod:os and :mod:os.path modules, and most other functions and
classes in the standard library. The :class:os.DirEntry class
and relevant classes in :mod:pathlib have also been updated to
implement :class:os.PathLike.
The hope is that updating the fundamental functions for operating
on file system paths will lead to third-party code to implicitly
support all :term:path-like objects <path-like object> without any
code changes, or at least very minimal ones (e.g. calling
:func:os.fspath at the beginning of code before operating on a
path-like object).
Here are some examples of how the new interface allows for
:class:pathlib.Path to be used more easily and transparently with
pre-existing code::
import pathlib with open(pathlib.Path("README")) as f: ... contents = f.read() ... import os.path os.path.splitext(pathlib.Path("some_file.txt")) ('some_file', '.txt') os.path.join("/a/b", pathlib.Path("c")) '/a/b/c' import os os.fspath(pathlib.Path("some_file.txt")) 'some_file.txt'
(Implemented by Brett Cannon, Ethan Furman, Dusty Phillips, and Jelle Zijlstra.)
.. seealso::
:pep:`519` -- Adding a file system path protocol
PEP written by Brett Cannon and Koos Zevenhoven.
.. _whatsnew36-pep495:
In most world locations, there have been and will be times when local clocks are moved back. In those times, intervals are introduced in which local clocks show the same time twice in the same day. In these situations, the information displayed on a local clock (or stored in a Python datetime instance) is insufficient to identify a particular moment in time.
:pep:495 adds the new fold attribute to instances of
:class:datetime.datetime and :class:datetime.time classes to differentiate
between two moments in time for which local times are the same::
>>> u0 = datetime(2016, 11, 6, 4, tzinfo=timezone.utc)
>>> for i in range(4):
... u = u0 + i*HOUR
... t = u.astimezone(Eastern)
... print(u.time(), 'UTC =', t.time(), t.tzname(), t.fold)
...
04:00:00 UTC = 00:00:00 EDT 0
05:00:00 UTC = 01:00:00 EDT 0
06:00:00 UTC = 01:00:00 EST 1
07:00:00 UTC = 02:00:00 EST 0
The values of the :attr:fold <datetime.datetime.fold> attribute have the
value 0 for all instances except those that represent the second
(chronologically) moment in time in an ambiguous case.
.. seealso::
:pep:495 -- Local Time Disambiguation
PEP written by Alexander Belopolsky and Tim Peters, implementation
by Alexander Belopolsky.
.. _whatsnew36-pep529:
Representing filesystem paths is best performed with str (Unicode) rather than bytes. However, there are some situations where using bytes is sufficient and correct.
Prior to Python 3.6, data loss could result when using bytes paths on Windows.
With this change, using bytes to represent paths is now supported on Windows,
provided those bytes are encoded with the encoding returned by
:func:sys.getfilesystemencoding(), which now defaults to 'utf-8'.
Applications that do not use str to represent paths should use
:func:os.fsencode() and :func:os.fsdecode() to ensure their bytes are
correctly encoded. To revert to the previous behaviour, set
:envvar:PYTHONLEGACYWINDOWSFSENCODING or call
:func:sys._enablelegacywindowsfsencoding.
See :pep:529 for more information and discussion of code modifications that
may be required.
.. _whatsnew36-pep528:
The default console on Windows will now accept all Unicode characters and
provide correctly read str objects to Python code. sys.stdin,
sys.stdout and sys.stderr now default to utf-8 encoding.
This change only applies when using an interactive console, and not when
redirecting files or pipes. To revert to the previous behaviour for interactive
console use, set :envvar:PYTHONLEGACYWINDOWSSTDIO.
.. seealso::
:pep:528 -- Change Windows console encoding to UTF-8
PEP written and implemented by Steve Dower.
.. _whatsnew36-pep520:
Attributes in a class definition body have a natural ordering: the same
order in which the names appear in the source. This order is now
preserved in the new class's :attr:~object.__dict__ attribute.
Also, the effective default class execution namespace (returned from
:ref:type.__prepare__() <prepare>) is now an insertion-order-preserving
mapping.
.. seealso::
:pep:520 -- Preserving Class Attribute Definition Order
PEP written and implemented by Eric Snow.
.. _whatsnew36-pep468:
**kwargs in a function signature is now guaranteed to be an
insertion-order-preserving mapping.
.. seealso::
:pep:468 -- Preserving Keyword Argument Order
PEP written and implemented by Eric Snow.
.. _whatsnew36-compactdict:
dict <typesmapping> implementationThe :ref:dict <typesmapping> type now uses a "compact" representation
based on a proposal by Raymond Hettinger <https://mail.python.org/pipermail/python-dev/2012-December/123028.html>_
which was first implemented by PyPy <https://morepypy.blogspot.com/2015/01/faster-more-memory-efficient-and-more.html>_.
The memory usage of the new :func:dict is between 20% and 25% smaller
compared to Python 3.5.
The order-preserving aspect of this new implementation is considered an implementation detail and should not be relied upon (this may change in the future, but it is desired to have this new dict implementation in the language for a few releases before changing the language spec to mandate order-preserving semantics for all current and future Python implementations; this also helps preserve backwards-compatibility with older versions of the language where random iteration order is still in effect, e.g. Python 3.5).
(Contributed by INADA Naoki in :issue:27350. Idea
originally suggested by Raymond Hettinger <https://mail.python.org/pipermail/python-dev/2012-December/123028.html>_.)
.. _whatsnew36-pep523:
While Python provides extensive support to customize how code executes, one place it has not done so is in the evaluation of frame objects. If you wanted some way to intercept frame evaluation in Python there really wasn't any way without directly manipulating function pointers for defined functions.
:pep:523 changes this by providing an API to make frame
evaluation pluggable at the C level. This will allow for tools such
as debuggers and JITs to intercept frame evaluation before the
execution of Python code begins. This enables the use of alternative
evaluation implementations for Python code, tracking frame
evaluation, etc.
This API is not part of the limited C API and is marked as private to signal that usage of this API is expected to be limited and only applicable to very select, low-level use-cases. Semantics of the API will change with Python as necessary.
.. seealso::
:pep:523 -- Adding a frame evaluation API to CPython
PEP written by Brett Cannon and Dino Viehland.
.. _whatsnew36-pythonmalloc:
The new :envvar:PYTHONMALLOC environment variable allows setting the Python
memory allocators and installing debug hooks.
It is now possible to install debug hooks on Python memory allocators on Python
compiled in release mode using PYTHONMALLOC=debug. Effects of debug hooks:
0xCB0xDBPyObject_Free called on a memory block allocated by
:c:func:PyMem_Malloc.GIL <global interpreter lock> is held when allocator
functions of :c:data:PYMEM_DOMAIN_OBJ (ex: :c:func:PyObject_Malloc) and
:c:data:PYMEM_DOMAIN_MEM (ex: :c:func:PyMem_Malloc) domains are called.Checking if the GIL is held is also a new feature of Python 3.6.
See the :c:func:PyMem_SetupDebugHooks function for debug hooks on Python
memory allocators.
It is now also possible to force the usage of the :c:func:malloc allocator of
the C library for all Python memory allocations using PYTHONMALLOC=malloc.
This is helpful when using external memory debuggers like Valgrind on
a Python compiled in release mode.
On error, the debug hooks on Python memory allocators now use the
:mod:tracemalloc module to get the traceback where a memory block was
allocated.
Example of fatal error on buffer overflow using
python3.6 -X tracemalloc=5 (store 5 frames in traces)::
Debug memory block at address p=0x7fbcd41666f8: API 'o'
4 bytes originally requested
The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
The 8 pad bytes at tail=0x7fbcd41666fc are not all FORBIDDENBYTE (0xfb):
at tail+0: 0x02 *** OUCH
at tail+1: 0xfb
at tail+2: 0xfb
at tail+3: 0xfb
at tail+4: 0xfb
at tail+5: 0xfb
at tail+6: 0xfb
at tail+7: 0xfb
The block was made by call #1233329 to debug malloc/realloc.
Data at p: 1a 2b 30 00
Memory block allocated at (most recent call first):
File "test/test_bytes.py", line 323
File "unittest/case.py", line 600
File "unittest/case.py", line 648
File "unittest/suite.py", line 122
File "unittest/suite.py", line 84
Fatal Python error: bad trailing pad byte
Current thread 0x00007fbcdbd32700 (most recent call first):
File "test/test_bytes.py", line 323 in test_hex
File "unittest/case.py", line 600 in run
File "unittest/case.py", line 648 in __call__
File "unittest/suite.py", line 122 in run
File "unittest/suite.py", line 84 in __call__
File "unittest/suite.py", line 122 in run
File "unittest/suite.py", line 84 in __call__
...
(Contributed by Victor Stinner in :issue:26516 and :issue:26564.)
.. _whatsnew36-tracing:
Python can now be built --with-dtrace which enables static markers
for the following events in the interpreter:
function call/return
garbage collection started/finished
line of code executed.
This can be used to instrument running interpreters in production, without the need to recompile specific debug builds or providing application-specific profiling/debugging code.
More details in :ref:instrumentation.
The current implementation is tested on Linux and macOS. Additional markers may be added in the future.
(Contributed by Łukasz Langa in :issue:21590, based on patches by
Jesús Cea Avión, David Malcolm, and Nikhil Benesch.)
Some smaller changes made to the core Python language are:
A global or nonlocal statement must now textually appear
before the first use of the affected name in the same scope.
Previously this was a :exc:SyntaxWarning.
It is now possible to set a :ref:special method <specialnames> to
None to indicate that the corresponding operation is not available.
For example, if a class sets :meth:__iter__ to None, the class
is not iterable.
(Contributed by Andrew Barnert and Ivan Levkivskyi in :issue:25958.)
Long sequences of repeated traceback lines are now abbreviated as
"[Previous line repeated {count} more times]" (see
:ref:whatsnew36-traceback for an example).
(Contributed by Emanuel Barry in :issue:26823.)
Import now raises the new exception :exc:ModuleNotFoundError
(subclass of :exc:ImportError) when it cannot find a module. Code
that currently checks for ImportError (in try-except) will still work.
(Contributed by Eric Snow in :issue:15767.)
Class methods relying on zero-argument super() will now work correctly
when called from metaclass methods during class creation.
(Contributed by Martin Teichmann in :issue:23722.)
.. _whatsnew36-pep506:
The main purpose of the new :mod:secrets module is to provide an obvious way
to reliably generate cryptographically strong pseudo-random values suitable
for managing secrets, such as account authentication, tokens, and similar.
.. warning::
Note that the pseudo-random generators in the :mod:random module
should NOT be used for security purposes. Use :mod:secrets
on Python 3.6+ and :func:os.urandom() on Python 3.5 and earlier.
.. seealso::
:pep:`506` -- Adding A Secrets Module To The Standard Library
PEP written and implemented by Steven D'Aprano.
Exhausted iterators of :class:array.array will now stay exhausted even
if the iterated array is extended. This is consistent with the behavior
of other mutable sequences.
Contributed by Serhiy Storchaka in :issue:26492.
The new :class:ast.Constant AST node has been added. It can be used
by external AST optimizers for the purposes of constant folding.
Contributed by Victor Stinner in :issue:26146.
Starting with Python 3.6 the asyncio module is no longer provisional and its
API is considered stable.
Notable changes in the :mod:asyncio module since Python 3.5.0
(all backported to 3.5.x due to the provisional status):
The :func:~asyncio.get_event_loop function has been changed to
always return the currently running loop when called from coroutines
and callbacks.
(Contributed by Yury Selivanov in :issue:28613.)
The :func:~asyncio.ensure_future function and all functions that
use it, such as :meth:loop.run_until_complete() <asyncio.loop.run_until_complete>,
now accept all kinds of :term:awaitable objects <awaitable>.
(Contributed by Yury Selivanov.)
New :func:~asyncio.run_coroutine_threadsafe function to submit
coroutines to event loops from other threads.
(Contributed by Vincent Michel.)
New :meth:Transport.is_closing() <asyncio.BaseTransport.is_closing>
method to check if the transport is closing or closed.
(Contributed by Yury Selivanov.)
The :meth:loop.create_server() <asyncio.loop.create_server>
method can now accept a list of hosts.
(Contributed by Yann Sionneau.)
New :meth:loop.create_future() <asyncio.loop.create_future>
method to create Future objects. This allows alternative event
loop implementations, such as
uvloop <https://github.com/MagicStack/uvloop>_, to provide a faster
:class:asyncio.Future implementation.
(Contributed by Yury Selivanov in :issue:27041.)
New :meth:loop.get_exception_handler() <asyncio.loop.get_exception_handler>
method to get the current exception handler.
(Contributed by Yury Selivanov in :issue:27040.)
New :meth:StreamReader.readuntil() <asyncio.StreamReader.readuntil>
method to read data from the stream until a separator bytes
sequence appears.
(Contributed by Mark Korenberg.)
The performance of :meth:StreamReader.readexactly() <asyncio.StreamReader.readexactly>
has been improved.
(Contributed by Mark Korenberg in :issue:28370.)
The :meth:loop.getaddrinfo() <asyncio.loop.getaddrinfo>
method is optimized to avoid calling the system getaddrinfo
function if the address is already resolved.
(Contributed by A. Jesse Jiryu Davis.)
The :meth:loop.stop() <asyncio.loop.stop>
method has been changed to stop the loop immediately after
the current iteration. Any new callbacks scheduled as a result
of the last iteration will be discarded.
(Contributed by Guido van Rossum in :issue:25593.)
:meth:Future.set_exception <asyncio.futures.Future.set_exception>
will now raise :exc:TypeError when passed an instance of
the :exc:StopIteration exception.
(Contributed by Chris Angelico in :issue:26221.)
New :meth:loop.connect_accepted_socket() <asyncio.loop.connect_accepted_socket>
method to be used by servers that accept connections outside of asyncio,
but that use asyncio to handle them.
(Contributed by Jim Fulton in :issue:27392.)
TCP_NODELAY flag is now set for all TCP transports by default.
(Contributed by Yury Selivanov in :issue:27456.)
New :meth:loop.shutdown_asyncgens() <asyncio.loop.shutdown_asyncgens>
to properly close pending asynchronous generators before closing the
loop.
(Contributed by Yury Selivanov in :issue:28003.)
:class:Future <asyncio.Future> and :class:Task <asyncio.Task>
classes now have an optimized C implementation which makes asyncio
code up to 30% faster.
(Contributed by Yury Selivanov and INADA Naoki in :issue:26081
and :issue:28544.)
The :func:~binascii.b2a_base64 function now accepts an optional newline
keyword argument to control whether the newline character is appended to the
return value.
(Contributed by Victor Stinner in :issue:25357.)
The new :const:cmath.tau (τ) constant has been added.
(Contributed by Lisa Roach in :issue:12345, see :pep:628 for details.)
New constants: :const:cmath.inf and :const:cmath.nan to
match :const:math.inf and :const:math.nan, and also :const:cmath.infj
and :const:cmath.nanj to match the format used by complex repr.
(Contributed by Mark Dickinson in :issue:23229.)
The new :class:~collections.abc.Collection abstract base class has been
added to represent sized iterable container classes.
(Contributed by Ivan Levkivskyi, docs by Neil Girdhar in :issue:27598.)
The new :class:~collections.abc.Reversible abstract base class represents
iterable classes that also provide the :meth:__reversed__ method.
(Contributed by Ivan Levkivskyi in :issue:25987.)
The new :class:~collections.abc.AsyncGenerator abstract base class represents
asynchronous generators.
(Contributed by Yury Selivanov in :issue:28720.)
The :func:~collections.namedtuple function now accepts an optional
keyword argument module, which, when specified, is used for
the __module__ attribute of the returned named tuple class.
(Contributed by Raymond Hettinger in :issue:17941.)
The verbose and rename arguments for
:func:~collections.namedtuple are now keyword-only.
(Contributed by Raymond Hettinger in :issue:25628.)
Recursive :class:collections.deque instances can now be pickled.
(Contributed by Serhiy Storchaka in :issue:26482.)
The :class:ThreadPoolExecutor <concurrent.futures.ThreadPoolExecutor>
class constructor now accepts an optional thread_name_prefix argument
to make it possible to customize the names of the threads created by the
pool.
(Contributed by Gregory P. Smith in :issue:27664.)
The :class:contextlib.AbstractContextManager class has been added to
provide an abstract base class for context managers. It provides a
sensible default implementation for __enter__() which returns
self and leaves __exit__() an abstract method. A matching
class has been added to the :mod:typing module as
:class:typing.ContextManager.
(Contributed by Brett Cannon in :issue:25609.)
The :class:~datetime.datetime and :class:~datetime.time classes have
the new :attr:~time.fold attribute used to disambiguate local time
when necessary. Many functions in the :mod:datetime have been
updated to support local time disambiguation.
See :ref:Local Time Disambiguation <whatsnew36-pep495> section for more
information.
(Contributed by Alexander Belopolsky in :issue:24773.)
The :meth:datetime.strftime() <datetime.datetime.strftime> and
:meth:date.strftime() <datetime.date.strftime> methods now support
ISO 8601 date directives %G, %u and %V.
(Contributed by Ashley Anderson in :issue:12006.)
The :func:datetime.isoformat() <datetime.datetime.isoformat> function
now accepts an optional timespec argument that specifies the number
of additional components of the time value to include.
(Contributed by Alessandro Cucci and Alexander Belopolsky in :issue:19475.)
The :meth:datetime.combine() <datetime.datetime.combine> now
accepts an optional tzinfo argument.
(Contributed by Alexander Belopolsky in :issue:27661.)
New :meth:Decimal.as_integer_ratio() <decimal.Decimal.as_integer_ratio>
method that returns a pair (n, d) of integers that represent the given
:class:~decimal.Decimal instance as a fraction, in lowest terms and
with a positive denominator::
>>> Decimal('-3.14').as_integer_ratio()
(-157, 50)
(Contributed by Stefan Krah amd Mark Dickinson in :issue:25928.)
The default_format attribute has been removed from
:class:distutils.command.sdist.sdist and the formats
attribute defaults to ['gztar']. Although not anticipated,
any code relying on the presence of default_format may
need to be adapted. See :issue:27819 for more details.
The new email API, enabled via the policy keyword to various constructors, is
no longer provisional. The :mod:email documentation has been reorganized and
rewritten to focus on the new API, while retaining the old documentation for
the legacy API. (Contributed by R. David Murray in :issue:24277.)
The :mod:email.mime classes now all accept an optional policy keyword.
(Contributed by Berker Peksag in :issue:27331.)
The :class:~email.generator.DecodedGenerator now supports the policy
keyword.
There is a new :mod:~email.policy attribute,
:attr:~email.policy.Policy.message_factory, that controls what class is used
by default when the parser creates new message objects. For the
:attr:email.policy.compat32 policy this is :class:~email.message.Message,
for the new policies it is :class:~email.message.EmailMessage.
(Contributed by R. David Murray in :issue:20476.)
On Windows, added the 'oem' encoding to use CP_OEMCP, and the 'ansi'
alias for the existing 'mbcs' encoding, which uses the CP_ACP code page.
(Contributed by Steve Dower in :issue:27959.)
Two new enumeration base classes have been added to the :mod:enum module:
:class:~enum.Flag and :class:~enum.IntFlags. Both are used to define
constants that can be combined using the bitwise operators.
(Contributed by Ethan Furman in :issue:23591.)
Many standard library modules have been updated to use the
:class:~enum.IntFlags class for their constants.
The new :class:enum.auto value can be used to assign values to enum
members automatically::
>>> from enum import Enum, auto
>>> class Color(Enum):
... red = auto()
... blue = auto()
... green = auto()
...
>>> list(Color)
[<Color.red: 1>, <Color.blue: 2>, <Color.green: 3>]
On Windows, the :mod:faulthandler module now installs a handler for Windows
exceptions: see :func:faulthandler.enable. (Contributed by Victor Stinner in
:issue:23848.)
:func:~fileinput.hook_encoded now supports the errors argument.
(Contributed by Joseph Hackman in :issue:25788.)
:mod:hashlib supports OpenSSL 1.1.0. The minimum recommend version is 1.0.2.
(Contributed by Christian Heimes in :issue:26470.)
BLAKE2 hash functions were added to the module. :func:~hashlib.blake2b
and :func:~hashlib.blake2s are always available and support the full
feature set of BLAKE2.
(Contributed by Christian Heimes in :issue:26798 based on code by
Dmitry Chestnykh and Samuel Neves. Documentation written by Dmitry Chestnykh.)
The SHA-3 hash functions :func:~hashlib.sha3_224, :func:~hashlib.sha3_256,
:func:~hashlib.sha3_384, :func:~hashlib.sha3_512, and SHAKE hash functions
:func:~hashlib.shake_128 and :func:~hashlib.shake_256 were added.
(Contributed by Christian Heimes in :issue:16113. Keccak Code Package
by Guido Bertoni, Joan Daemen, Michaël Peeters, Gilles Van Assche, and
Ronny Van Keer.)
The password-based key derivation function :func:~hashlib.scrypt is now
available with OpenSSL 1.1.0 and newer.
(Contributed by Christian Heimes in :issue:27928.)
:meth:HTTPConnection.request() <http.client.HTTPConnection.request> and
:meth:~http.client.HTTPConnection.endheaders both now support
chunked encoding request bodies.
(Contributed by Demian Brecht and Rolf Krahl in :issue:12319.)
The idlelib package is being modernized and refactored to make IDLE look and work better and to make the code easier to understand, test, and improve. Part of making IDLE look better, especially on Linux and Mac, is using ttk widgets, mostly in the dialogs. As a result, IDLE no longer runs with tcl/tk 8.4. It now requires tcl/tk 8.5 or 8.6. We recommend running the latest release of either.
'Modernizing' includes renaming and consolidation of idlelib modules. The
renaming of files with partial uppercase names is similar to the renaming of,
for instance, Tkinter and TkFont to tkinter and tkinter.font in 3.0. As a
result, imports of idlelib files that worked in 3.5 will usually not work in
3.6. At least a module name change will be needed (see idlelib/README.txt),
sometimes more. (Name changes contributed by Al Swiegart and Terry Reedy in
:issue:24225. Most idlelib patches since have been and will be part of the
process.)
In compensation, the eventual result with be that some idlelib classes will be easier to use, with better APIs and docstrings explaining them. Additional useful information will be added to idlelib when available.
New in 3.6.2:
Multiple fixes for autocompletion. (Contributed by Louie Lu in :issue:15786.)
New in 3.6.3:
Module Browser (on the File menu, formerly called Class Browser),
now displays nested functions and classes in addition to top-level
functions and classes.
(Contributed by Guilherme Polo, Cheryl Sabella, and Terry Jan Reedy
in :issue:1612262.)
The IDLE features formerly implemented as extensions have been reimplemented
as normal features. Their settings have been moved from the Extensions tab
to other dialog tabs.
(Contributed by Charles Wohlganger and Terry Jan Reedy in :issue:27099.)
The Settings dialog (Options, Configure IDLE) has been partly rewritten to improve both appearance and function. (Contributed by Cheryl Sabella and Terry Jan Reedy in multiple issues.)
New in 3.6.4:
The font sample now includes a selection of non-Latin characters so that
users can better see the effect of selecting a particular font.
(Contributed by Terry Jan Reedy in :issue:13802.)
The sample can be edited to include other characters.
(Contributed by Serhiy Storchaka in :issue:31860.)
New in 3.6.6:
Editor code context option revised. Box displays all context lines up to
maxlines. Clicking on a context line jumps the editor to that line. Context
colors for custom themes is added to Highlights tab of Settings dialog.
(Contributed by Cheryl Sabella and Terry Jan Reedy in :issue:33642,
:issue:33768, and :issue:33679.)
On Windows, a new API call tells Windows that tk scales for DPI. On Windows
8.1+ or 10, with DPI compatibility properties of the Python binary
unchanged, and a monitor resolution greater than 96 DPI, this should
make text and lines sharper. It should otherwise have no effect.
(Contributed by Terry Jan Reedy in :issue:33656.)
New in 3.6.7:
Output over N lines (50 by default) is squeezed down to a button.
N can be changed in the PyShell section of the General page of the
Settings dialog. Fewer, but possibly extra long, lines can be squeezed by
right clicking on the output. Squeezed output can be expanded in place
by double-clicking the button or into the clipboard or a separate window
by right-clicking the button. (Contributed by Tal Einat in :issue:1529353.)
Import now raises the new exception :exc:ModuleNotFoundError
(subclass of :exc:ImportError) when it cannot find a module. Code
that current checks for ImportError (in try-except) will still work.
(Contributed by Eric Snow in :issue:15767.)
:class:importlib.util.LazyLoader now calls
:meth:~importlib.abc.Loader.create_module on the wrapped loader, removing the
restriction that :class:importlib.machinery.BuiltinImporter and
:class:importlib.machinery.ExtensionFileLoader couldn't be used with
:class:importlib.util.LazyLoader.
:func:importlib.util.cache_from_source,
:func:importlib.util.source_from_cache, and
:func:importlib.util.spec_from_file_location now accept a
:term:path-like object.
The :func:inspect.signature() <inspect.signature> function now reports the
implicit .0 parameters generated by the compiler for comprehension and
generator expression scopes as if they were positional-only parameters called
implicit0. (Contributed by Jelle Zijlstra in :issue:19611.)
To reduce code churn when upgrading from Python 2.7 and the legacy
:func:inspect.getargspec API, the previously documented deprecation of
:func:inspect.getfullargspec has been reversed. While this function is
convenient for single/source Python 2/3 code bases, the richer
:func:inspect.signature interface remains the recommended approach for new
code. (Contributed by Nick Coghlan in :issue:27172)
:func:json.load and :func:json.loads now support binary input. Encoded
JSON should be represented using either UTF-8, UTF-16, or UTF-32.
(Contributed by Serhiy Storchaka in :issue:17909.)
The new :meth:WatchedFileHandler.reopenIfNeeded() <logging.handlers.WatchedFileHandler.reopenIfNeeded>
method has been added to add the ability to check if the log file needs to
be reopened.
(Contributed by Marian Horban in :issue:24884.)
The tau (τ) constant has been added to the :mod:math and :mod:cmath
modules.
(Contributed by Lisa Roach in :issue:12345, see :pep:628 for details.)
:ref:Proxy Objects <multiprocessing-proxy_objects> returned by
:func:multiprocessing.Manager can now be nested.
(Contributed by Davin Potts in :issue:6766.)
See the summary of :ref:PEP 519 <whatsnew36-pep519> for details on how the
:mod:os and :mod:os.path modules now support
:term:path-like objects <path-like object>.
:func:~os.scandir now supports :class:bytes paths on Windows.
A new :meth:~os.scandir.close method allows explicitly closing a
:func:~os.scandir iterator. The :func:~os.scandir iterator now
supports the :term:context manager protocol. If a :func:scandir
iterator is neither exhausted nor explicitly closed a :exc:ResourceWarning
will be emitted in its destructor.
(Contributed by Serhiy Storchaka in :issue:25994.)
On Linux, :func:os.urandom now blocks until the system urandom entropy pool
is initialized to increase the security. See the :pep:524 for the rationale.
The Linux getrandom() syscall (get random bytes) is now exposed as the new
:func:os.getrandom function.
(Contributed by Victor Stinner, part of the :pep:524)
:mod:pathlib now supports :term:path-like objects <path-like object>.
(Contributed by Brett Cannon in :issue:27186.)
See the summary of :ref:PEP 519 <whatsnew36-pep519> for details.
The :class:~pdb.Pdb class constructor has a new optional readrc argument
to control whether .pdbrc files should be read.
Objects that need __new__ called with keyword arguments can now be pickled
using :ref:pickle protocols <pickle-protocols> older than protocol version 4.
Protocol version 4 already supports this case. (Contributed by Serhiy
Storchaka in :issue:24164.)
:func:pickletools.dis() now outputs the implicit memo index for the
MEMOIZE opcode.
(Contributed by Serhiy Storchaka in :issue:25382.)
The :mod:pydoc module has learned to respect the MANPAGER
environment variable.
(Contributed by Matthias Klose in :issue:8637.)
:func:help and :mod:pydoc can now list named tuple fields in the
order they were defined rather than alphabetically.
(Contributed by Raymond Hettinger in :issue:24879.)
The new :func:~random.choices function returns a list of elements of
specified size from the given population with optional weights.
(Contributed by Raymond Hettinger in :issue:18844.)
Added support of modifier spans in regular expressions. Examples:
'(?i:p)ython' matches 'python' and 'Python', but not 'PYTHON';
'(?i)g(?-i:v)r' matches 'GvR' and 'gvr', but not 'GVR'.
(Contributed by Serhiy Storchaka in :issue:433028.)
Match object groups can be accessed by __getitem__, which is
equivalent to group(). So mo['name'] is now equivalent to
mo.group('name'). (Contributed by Eric Smith in :issue:24454.)
:class:~re.Match objects now support
:meth:index-like objects <object.__index__> as group
indices.
(Contributed by Jeroen Demeyer and Xiang Zhang in :issue:27177.)
Added :func:~readline.set_auto_history to enable or disable
automatic addition of input to the history list. (Contributed by
Tyler Crompton in :issue:26870.)
Private and special attribute names now are omitted unless the prefix starts
with underscores. A space or a colon is added after some completed keywords.
(Contributed by Serhiy Storchaka in :issue:25011 and :issue:25209.)
The :class:~shlex.shlex has much
:ref:improved shell compatibility <improved-shell-compatibility>
through the new punctuation_chars argument to control which characters
are treated as punctuation.
(Contributed by Vinay Sajip in :issue:1521950.)
When specifying paths to add to :attr:sys.path in a .pth file,
you may now specify file paths on top of directories (e.g. zip files).
(Contributed by Wolfgang Langner in :issue:26587).
:attr:sqlite3.Cursor.lastrowid now supports the REPLACE statement.
(Contributed by Alex LordThorsen in :issue:16864.)
The :func:~socket.socket.ioctl function now supports the
:data:~socket.SIO_LOOPBACK_FAST_PATH control code.
(Contributed by Daniel Stokes in :issue:26536.)
The :meth:~socket.socket.getsockopt constants SO_DOMAIN,
SO_PROTOCOL, SO_PEERSEC, and SO_PASSSEC are now supported.
(Contributed by Christian Heimes in :issue:26907.)
The :meth:~socket.socket.setsockopt now supports the
setsockopt(level, optname, None, optlen: int) form.
(Contributed by Christian Heimes in :issue:27744.)
The socket module now supports the address family
:data:~socket.AF_ALG to interface with Linux Kernel crypto API. ALG_*,
SOL_ALG and :meth:~socket.socket.sendmsg_afalg were added.
(Contributed by Christian Heimes in :issue:27744 with support from
Victor Stinner.)
New Linux constants TCP_USER_TIMEOUT and TCP_CONGESTION were added.
(Contributed by Omar Sandoval, issue:26273).
Servers based on the :mod:socketserver module, including those
defined in :mod:http.server, :mod:xmlrpc.server and
:mod:wsgiref.simple_server, now support the :term:context manager
protocol.
(Contributed by Aviv Palivoda in :issue:26404.)
The :attr:~socketserver.StreamRequestHandler.wfile attribute of
:class:~socketserver.StreamRequestHandler classes now implements
the :class:io.BufferedIOBase writable interface. In particular,
calling :meth:~io.BufferedIOBase.write is now guaranteed to send the
data in full. (Contributed by Martin Panter in :issue:26721.)
:mod:ssl supports OpenSSL 1.1.0. The minimum recommend version is 1.0.2.
(Contributed by Christian Heimes in :issue:26470.)
3DES has been removed from the default cipher suites and ChaCha20 Poly1305
cipher suites have been added.
(Contributed by Christian Heimes in :issue:27850 and :issue:27766.)
:class:~ssl.SSLContext has better default configuration for options
and ciphers.
(Contributed by Christian Heimes in :issue:28043.)
SSL session can be copied from one client-side connection to another
with the new :class:~ssl.SSLSession class. TLS session resumption can
speed up the initial handshake, reduce latency and improve performance
(Contributed by Christian Heimes in :issue:19500 based on a draft by
Alex Warhawk.)
The new :meth:~ssl.SSLContext.get_ciphers method can be used to
get a list of enabled ciphers in order of cipher priority.
All constants and flags have been converted to :class:~enum.IntEnum and
:class:~enum.IntFlags.
(Contributed by Christian Heimes in :issue:28025.)
Server and client-side specific TLS protocols for :class:~ssl.SSLContext
were added.
(Contributed by Christian Heimes in :issue:28085.)
A new :func:~statistics.harmonic_mean function has been added.
(Contributed by Steven D'Aprano in :issue:27181.)
:mod:struct now supports IEEE 754 half-precision floats via the 'e'
format specifier.
(Contributed by Eli Stevens, Mark Dickinson in :issue:11734.)
:class:subprocess.Popen destructor now emits a :exc:ResourceWarning warning
if the child process is still running. Use the context manager protocol (with proc: ...) or explicitly call the :meth:~subprocess.Popen.wait method to
read the exit status of the child process. (Contributed by Victor Stinner in
:issue:26741.)
The :class:subprocess.Popen constructor and all functions that pass arguments
through to it now accept encoding and errors arguments. Specifying either
of these will enable text mode for the stdin, stdout and stderr streams.
(Contributed by Steve Dower in :issue:6135.)
The new :func:~sys.getfilesystemencodeerrors function returns the name of
the error mode used to convert between Unicode filenames and bytes filenames.
(Contributed by Steve Dower in :issue:27781.)
On Windows the return value of the :func:~sys.getwindowsversion function
now includes the platform_version field which contains the accurate major
version, minor version and build number of the current operating system,
rather than the version that is being emulated for the process
(Contributed by Steve Dower in :issue:27932.)
:class:~telnetlib.Telnet is now a context manager (contributed by
Stéphane Wirtel in :issue:25485).
The :class:~time.struct_time attributes :attr:tm_gmtoff and
:attr:tm_zone are now available on all platforms.
The new :meth:Timer.autorange() <timeit.Timer.autorange> convenience
method has been added to call :meth:Timer.timeit() <timeit.Timer.timeit>
repeatedly so that the total run time is greater or equal to 200 milliseconds.
(Contributed by Steven D'Aprano in :issue:6422.)
:mod:timeit now warns when there is substantial (4x) variance
between best and worst times.
(Contributed by Serhiy Storchaka in :issue:23552.)
Added methods :meth:~tkinter.Variable.trace_add,
:meth:~tkinter.Variable.trace_remove and :meth:~tkinter.Variable.trace_info
in the :class:tkinter.Variable class. They replace old methods
:meth:~tkinter.Variable.trace_variable, :meth:~tkinter.Variable.trace,
:meth:~tkinter.Variable.trace_vdelete and
:meth:~tkinter.Variable.trace_vinfo that use obsolete Tcl commands and might
not work in future versions of Tcl.
(Contributed by Serhiy Storchaka in :issue:22115).
.. _whatsnew36-traceback:
Both the traceback module and the interpreter's builtin exception display now abbreviate long sequences of repeated lines in tracebacks as shown in the following example::
>>> def f(): f()
...
>>> f()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 1, in f
File "<stdin>", line 1, in f
File "<stdin>", line 1, in f
[Previous line repeated 995 more times]
RecursionError: maximum recursion depth exceeded
(Contributed by Emanuel Barry in :issue:26823.)
The :mod:tracemalloc module now supports tracing memory allocations in
multiple different address spaces.
The new :class:~tracemalloc.DomainFilter filter class has been added
to filter block traces by their address space (domain).
(Contributed by Victor Stinner in :issue:26588.)
.. _whatsnew36-typing:
Since the :mod:typing module is :term:provisional <provisional api>,
all changes introduced in Python 3.6 have also been
backported to Python 3.5.x.
The :mod:typing module has a much improved support for generic type
aliases. For example Dict[str, Tuple[S, T]] is now a valid
type annotation.
(Contributed by Guido van Rossum in Github #195 <https://github.com/python/typing/pull/195>_.)
The :class:typing.ContextManager class has been added for
representing :class:contextlib.AbstractContextManager.
(Contributed by Brett Cannon in :issue:25609.)
The :class:typing.Collection class has been added for
representing :class:collections.abc.Collection.
(Contributed by Ivan Levkivskyi in :issue:27598.)
The :const:typing.ClassVar type construct has been added to
mark class variables. As introduced in :pep:526, a variable annotation
wrapped in ClassVar indicates that a given attribute is intended to be used as
a class variable and should not be set on instances of that class.
(Contributed by Ivan Levkivskyi in Github #280 <https://github.com/python/typing/pull/280>_.)
A new :const:~typing.TYPE_CHECKING constant that is assumed to be
True by the static type checkers, but is False at runtime.
(Contributed by Guido van Rossum in Github #230 <https://github.com/python/typing/issues/230>_.)
A new :func:~typing.NewType helper function has been added to create
lightweight distinct types for annotations::
from typing import NewType
UserId = NewType('UserId', int)
some_id = UserId(524313)
The static type checker will treat the new type as if it were a subclass
of the original type. (Contributed by Ivan Levkivskyi in Github #189 <https://github.com/python/typing/issues/189>_.)
The :mod:unicodedata module now uses data from Unicode 9.0.0 <http://unicode.org/versions/Unicode9.0.0/>_.
(Contributed by Benjamin Peterson.)
The :class:~unittest.mock.Mock class has the following improvements:
Two new methods, :meth:Mock.assert_called() <unittest.mock.Mock.assert_called> and :meth:Mock.assert_called_once() <unittest.mock.Mock.assert_called_once> to check if the mock object
was called.
(Contributed by Amit Saha in :issue:26323.)
The :meth:Mock.reset_mock() <unittest.mock.Mock.reset_mock> method
now has two optional keyword only arguments: return_value and
side_effect.
(Contributed by Kushal Das in :issue:21271.)
If a HTTP request has a file or iterable body (other than a
bytes object) but no Content-Length header, rather than
throwing an error, :class:~urllib.request.AbstractHTTPHandler now
falls back to use chunked transfer encoding.
(Contributed by Demian Brecht and Rolf Krahl in :issue:12319.)
:class:~urllib.robotparser.RobotFileParser now supports the Crawl-delay and
Request-rate extensions.
(Contributed by Nikolay Bogoychev in :issue:16099.)
:mod:venv accepts a new parameter --prompt. This parameter provides an
alternative prefix for the virtual environment. (Proposed by Łukasz Balcerzak
and ported to 3.6 by Stéphane Wirtel in :issue:22829.)
A new optional source parameter has been added to the
:func:warnings.warn_explicit function: the destroyed object which emitted a
:exc:ResourceWarning. A source attribute has also been added to
:class:warnings.WarningMessage (contributed by Victor Stinner in
:issue:26568 and :issue:26567).
When a :exc:ResourceWarning warning is logged, the :mod:tracemalloc module is now
used to try to retrieve the traceback where the destroyed object was allocated.
Example with the script example.py::
import warnings
def func():
return open(__file__)
f = func()
f = None
Output of the command python3.6 -Wd -X tracemalloc=5 example.py::
example.py:7: ResourceWarning: unclosed file <_io.TextIOWrapper name='example.py' mode='r' encoding='UTF-8'>
f = None
Object allocated at (most recent call first):
File "example.py", lineno 4
return open(__file__)
File "example.py", lineno 6
f = func()
The "Object allocated at" traceback is new and is only displayed if
:mod:tracemalloc is tracing Python memory allocations and if the
:mod:warnings module was already imported.
Added the 64-bit integer type :data:REG_QWORD <winreg.REG_QWORD>.
(Contributed by Clement Rouault in :issue:23026.)
Allowed keyword arguments to be passed to :func:Beep <winsound.Beep>,
:func:MessageBeep <winsound.MessageBeep>, and :func:PlaySound <winsound.PlaySound> (:issue:27982).
The :mod:xmlrpc.client module now supports unmarshalling
additional data types used by the Apache XML-RPC implementation
for numerics and None.
(Contributed by Serhiy Storchaka in :issue:26885.)
A new :meth:ZipInfo.from_file() <zipfile.ZipInfo.from_file> class method
allows making a :class:~zipfile.ZipInfo instance from a filesystem file.
A new :meth:ZipInfo.is_dir() <zipfile.ZipInfo.is_dir> method can be used
to check if the :class:~zipfile.ZipInfo instance represents a directory.
(Contributed by Thomas Kluyver in :issue:26039.)
The :meth:ZipFile.open() <zipfile.ZipFile.open> method can now be used to
write data into a ZIP file, as well as for extracting data.
(Contributed by Thomas Kluyver in :issue:26039.)
The :func:~zlib.compress and :func:~zlib.decompress functions now accept
keyword arguments.
(Contributed by Aviv Palivoda in :issue:26243 and
Xiang Zhang in :issue:16764 respectively.)
The Python interpreter now uses a 16-bit wordcode instead of bytecode which
made a number of opcode optimizations possible.
(Contributed by Demur Rumed with input and reviews from
Serhiy Storchaka and Victor Stinner in :issue:26647 and :issue:28050.)
The :class:asyncio.Future class now has an optimized C implementation.
(Contributed by Yury Selivanov and INADA Naoki in :issue:26081.)
The :class:asyncio.Task class now has an optimized
C implementation. (Contributed by Yury Selivanov in :issue:28544.)
Various implementation improvements in the :mod:typing module
(such as caching of generic types) allow up to 30 times performance
improvements and reduced memory footprint.
The ASCII decoder is now up to 60 times as fast for error handlers
surrogateescape, ignore and replace (Contributed
by Victor Stinner in :issue:24870).
The ASCII and the Latin1 encoders are now up to 3 times as fast for the
error handler surrogateescape
(Contributed by Victor Stinner in :issue:25227).
The UTF-8 encoder is now up to 75 times as fast for error handlers
ignore, replace, surrogateescape, surrogatepass (Contributed
by Victor Stinner in :issue:25267).
The UTF-8 decoder is now up to 15 times as fast for error handlers
ignore, replace and surrogateescape (Contributed
by Victor Stinner in :issue:25301).
bytes % args is now up to 2 times faster. (Contributed by Victor Stinner
in :issue:25349).
bytearray % args is now between 2.5 and 5 times faster. (Contributed by
Victor Stinner in :issue:25399).
Optimize :meth:bytes.fromhex and :meth:bytearray.fromhex: they are now
between 2x and 3.5x faster. (Contributed by Victor Stinner in :issue:25401).
Optimize bytes.replace(b'', b'.') and bytearray.replace(b'', b'.'):
up to 80% faster. (Contributed by Josh Snider in :issue:26574).
Allocator functions of the :c:func:PyMem_Malloc domain
(:c:data:PYMEM_DOMAIN_MEM) now use the :ref:pymalloc memory allocator <pymalloc> instead of :c:func:malloc function of the C library. The
pymalloc allocator is optimized for objects smaller or equal to 512 bytes
with a short lifetime, and use :c:func:malloc for larger memory blocks.
(Contributed by Victor Stinner in :issue:26249).
:func:pickle.load and :func:pickle.loads are now up to 10% faster when
deserializing many small objects (Contributed by Victor Stinner in
:issue:27056).
Passing :term:keyword arguments <keyword argument> to a function has an
overhead in comparison with passing :term:positional arguments <positional argument>. Now in extension functions implemented with using
Argument Clinic this overhead is significantly decreased.
(Contributed by Serhiy Storchaka in :issue:27574).
Optimized :func:~glob.glob and :func:~glob.iglob functions in the
:mod:glob module; they are now about 3--6 times faster.
(Contributed by Serhiy Storchaka in :issue:25596).
Optimized globbing in :mod:pathlib by using :func:os.scandir;
it is now about 1.5--4 times faster.
(Contributed by Serhiy Storchaka in :issue:26032).
:class:xml.etree.ElementTree parsing, iteration and deepcopy performance
has been significantly improved.
(Contributed by Serhiy Storchaka in :issue:25638, :issue:25873,
and :issue:25869.)
Creation of :class:fractions.Fraction instances from floats and
decimals is now 2 to 3 times faster.
(Contributed by Serhiy Storchaka in :issue:25971.)
Python now requires some C99 support in the toolchain to build.
Most notably, Python now uses standard integer types and macros in
place of custom macros like PY_LONG_LONG.
For more information, see :pep:7 and :issue:17884.
Cross-compiling CPython with the Android NDK and the Android API level set to
21 (Android 5.0 Lollipop) or greater runs successfully. While Android is not
yet a supported platform, the Python test suite runs on the Android emulator
with only about 16 tests failures. See the Android meta-issue :issue:26865.
The --enable-optimizations configure flag has been added. Turning it on
will activate expensive optimizations like PGO.
(Original patch by Alecsandru Patrascu of Intel in :issue:26359.)
The :term:GIL <global interpreter lock> must now be held when allocator
functions of :c:data:PYMEM_DOMAIN_OBJ (ex: :c:func:PyObject_Malloc) and
:c:data:PYMEM_DOMAIN_MEM (ex: :c:func:PyMem_Malloc) domains are called.
New :c:func:Py_FinalizeEx API which indicates if flushing buffered data
failed.
(Contributed by Martin Panter in :issue:5319.)
:c:func:PyArg_ParseTupleAndKeywords now supports :ref:positional-only parameters <positional-only_parameter>. Positional-only parameters are
defined by empty names.
(Contributed by Serhiy Storchaka in :issue:26282).
PyTraceback_Print method now abbreviates long sequences of repeated lines
as "[Previous line repeated {count} more times]".
(Contributed by Emanuel Barry in :issue:26823.)
The new :c:func:PyErr_SetImportErrorSubclass function allows for
specifying a subclass of :exc:ImportError to raise.
(Contributed by Eric Snow in :issue:15767.)
The new :c:func:PyErr_ResourceWarning function can be used to generate
a :exc:ResourceWarning providing the source of the resource allocation.
(Contributed by Victor Stinner in :issue:26567.)
The new :c:func:PyOS_FSPath function returns the file system
representation of a :term:path-like object.
(Contributed by Brett Cannon in :issue:27186.)
The :c:func:PyUnicode_FSConverter and :c:func:PyUnicode_FSDecoder
functions will now accept :term:path-like objects <path-like object>.
When :option:--version (short form: :option:-V) is supplied twice,
Python prints :data:sys.version for detailed information.
.. code-block:: shell-session
$ ./python -VV Python 3.6.0b4+ (3.6:223967b49e49+, Nov 21 2016, 20:55:04) [GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]
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. Starting in Python 3.6, the use of
async or await as names will generate a :exc:DeprecationWarning.
Raising the :exc:StopIteration exception inside a generator will now
generate a :exc:DeprecationWarning, and will trigger a :exc:RuntimeError
in Python 3.7. See :ref:whatsnew-pep-479 for details.
The :meth:__aiter__ method is now expected to return an asynchronous
iterator directly instead of returning an awaitable as previously.
Doing the former will trigger a :exc:DeprecationWarning. Backward
compatibility will be removed in Python 3.7.
(Contributed by Yury Selivanov in :issue:27243.)
A backslash-character pair that is not a valid escape sequence now generates
a :exc:DeprecationWarning. Although this will eventually become a
:exc:SyntaxError, that will not be for several Python releases.
(Contributed by Emanuel Barry in :issue:27364.)
When performing a relative import, falling back on __name__ and
__path__ from the calling module when __spec__ or
__package__ are not defined now raises an :exc:ImportWarning.
(Contributed by Rose Ames in :issue:25791.)
asynchat
The :mod:`asynchat` has been deprecated in favor of :mod:`asyncio`.
(Contributed by Mariatta in :issue:`25002`.)
asyncore
The :mod:asyncore has been deprecated in favor of :mod:asyncio.
(Contributed by Mariatta in :issue:25002.)
dbm
Unlike other :mod:`dbm` implementations, the :mod:`dbm.dumb` module
creates databases with the ``'rw'`` mode and allows modifying the database
opened with the ``'r'`` mode. This behavior is now deprecated and will
be removed in 3.8.
(Contributed by Serhiy Storchaka in :issue:`21708`.)
distutils
The undocumented extra_path argument to the
:class:~distutils.Distribution constructor is now considered deprecated
and will raise a warning if set. Support for this parameter will be
removed in a future Python release. See :issue:27919 for details.
grp
The support of non-integer arguments in :func:`~grp.getgrgid` has been
deprecated.
(Contributed by Serhiy Storchaka in :issue:`26129`.)
importlib
The :meth:importlib.machinery.SourceFileLoader.load_module and
:meth:importlib.machinery.SourcelessFileLoader.load_module methods
are now deprecated. They were the only remaining implementations of
:meth:importlib.abc.Loader.load_module in :mod:importlib that had not
been deprecated in previous versions of Python in favour of
:meth:importlib.abc.Loader.exec_module.
The :class:importlib.machinery.WindowsRegistryFinder class is now
deprecated. As of 3.6.0, it is still added to :attr:sys.meta_path by
default (on Windows), but this may change in future releases.
os ~~
Undocumented support of general :term:bytes-like objects <bytes-like object>
as paths in :mod:os functions, :func:compile and similar functions is
now deprecated.
(Contributed by Serhiy Storchaka in :issue:25791 and :issue:26754.)
re ~~
Support for inline flags (?letters) in the middle of the regular
expression has been deprecated and will be removed in a future Python
version. Flags at the start of a regular expression are still allowed.
(Contributed by Serhiy Storchaka in :issue:22493.)
ssl
OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported.
In the future the :mod:`ssl` module will require at least OpenSSL 1.0.2 or
1.1.0.
SSL-related arguments like ``certfile``, ``keyfile`` and ``check_hostname``
in :mod:`ftplib`, :mod:`http.client`, :mod:`imaplib`, :mod:`poplib`,
and :mod:`smtplib` have been deprecated in favor of ``context``.
(Contributed by Christian Heimes in :issue:`28022`.)
A couple of protocols and functions of the :mod:`ssl` module are now
deprecated. Some features will no longer be available in future versions
of OpenSSL. Other features are deprecated in favor of a different API.
(Contributed by Christian Heimes in :issue:`28022` and :issue:`26470`.)
tkinter
The :mod:tkinter.tix module is now deprecated. :mod:tkinter users
should use :mod:tkinter.ttk instead.
venv
The ``pyvenv`` script has been deprecated in favour of ``python3 -m venv``.
This prevents confusion as to what Python interpreter ``pyvenv`` is
connected to and thus what Python interpreter will be used by the virtual
environment. (Contributed by Brett Cannon in :issue:`25154`.)
Deprecated functions and types of the C API
-------------------------------------------
Undocumented functions :c:func:`PyUnicode_AsEncodedObject`,
:c:func:`PyUnicode_AsDecodedObject`, :c:func:`PyUnicode_AsEncodedUnicode`
and :c:func:`PyUnicode_AsDecodedUnicode` are deprecated now.
Use the :ref:`generic codec based API <codec-registry>` instead.
Deprecated Build Options
------------------------
The ``--with-system-ffi`` configure flag is now on by default on non-macOS
UNIX platforms. It may be disabled by using ``--without-system-ffi``, but
using the flag is deprecated and will not be accepted in Python 3.7.
macOS is unaffected by this change. Note that many OS distributors already
use the ``--with-system-ffi`` flag when building their system Python.
Removed
=======
API and Feature Removals
------------------------
* Unknown escapes consisting of ``'\'`` and an ASCII letter in
regular expressions will now cause an error. In replacement templates for
:func:`re.sub` they are still allowed, but deprecated.
The :const:`re.LOCALE` flag can now only be used with binary patterns.
* ``inspect.getmoduleinfo()`` was removed (was deprecated since CPython 3.3).
:func:`inspect.getmodulename` should be used for obtaining the module
name for a given path.
(Contributed by Yury Selivanov in :issue:`13248`.)
* ``traceback.Ignore`` class and ``traceback.usage``, ``traceback.modname``,
``traceback.fullmodname``, ``traceback.find_lines_from_code``,
``traceback.find_lines``, ``traceback.find_strings``,
``traceback.find_executable_lines`` methods were removed from the
:mod:`traceback` module. They were undocumented methods deprecated since
Python 3.2 and equivalent functionality is available from private methods.
* The ``tk_menuBar()`` and ``tk_bindForTraversal()`` dummy methods in
:mod:`tkinter` widget classes were removed (corresponding Tk commands
were obsolete since Tk 4.0).
* The :meth:`~zipfile.ZipFile.open` method of the :class:`zipfile.ZipFile`
class no longer supports the ``'U'`` mode (was deprecated since Python 3.4).
Use :class:`io.TextIOWrapper` for reading compressed text files in
:term:`universal newlines` mode.
* The undocumented ``IN``, ``CDROM``, ``DLFCN``, ``TYPES``, ``CDIO``, and
``STROPTS`` modules have been removed. They had been available in the
platform specific ``Lib/plat-*/`` directories, but were chronically out of
date, inconsistently available across platforms, and unmaintained. The
script that created these modules is still available in the source
distribution at :source:`Tools/scripts/h2py.py`.
* The deprecated ``asynchat.fifo`` class has been removed.
Porting to Python 3.6
=====================
This section lists previously described changes and other bugfixes
that may require changes to your code.
Changes in 'python' Command Behavior
------------------------------------
* The output of a special Python build with defined ``COUNT_ALLOCS``,
``SHOW_ALLOC_COUNT`` or ``SHOW_TRACK_COUNT`` macros is now off by
default. It can be re-enabled using the ``-X showalloccount`` option.
It now outputs to ``stderr`` instead of ``stdout``.
(Contributed by Serhiy Storchaka in :issue:`23034`.)
Changes in the Python API
-------------------------
* :func:`open() <open>` will no longer allow combining the ``'U'`` mode flag
with ``'+'``.
(Contributed by Jeff Balogh and John O'Connor in :issue:`2091`.)
* :mod:`sqlite3` no longer implicitly commits an open transaction before DDL
statements.
* On Linux, :func:`os.urandom` now blocks until the system urandom entropy pool
is initialized to increase the security.
* When :meth:`importlib.abc.Loader.exec_module` is defined,
:meth:`importlib.abc.Loader.create_module` must also be defined.
* :c:func:`PyErr_SetImportError` now sets :exc:`TypeError` when its **msg**
argument is not set. Previously only ``NULL`` was returned.
* The format of the ``co_lnotab`` attribute of code objects changed to support
a negative line number delta. By default, Python does not emit bytecode with
a negative line number delta. Functions using ``frame.f_lineno``,
``PyFrame_GetLineNumber()`` or ``PyCode_Addr2Line()`` are not affected.
Functions directly decoding ``co_lnotab`` should be updated to use a signed
8-bit integer type for the line number delta, but this is only required to
support applications using a negative line number delta. See
``Objects/lnotab_notes.txt`` for the ``co_lnotab`` format and how to decode
it, and see the :pep:`511` for the rationale.
* The functions in the :mod:`compileall` module now return booleans instead
of ``1`` or ``0`` to represent success or failure, respectively. Thanks to
booleans being a subclass of integers, this should only be an issue if you
were doing identity checks for ``1`` or ``0``. See :issue:`25768`.
* Reading the :attr:`~urllib.parse.SplitResult.port` attribute of
:func:`urllib.parse.urlsplit` and :func:`~urllib.parse.urlparse` results
now raises :exc:`ValueError` for out-of-range values, rather than
returning :const:`None`. See :issue:`20059`.
* The :mod:`imp` module now raises a :exc:`DeprecationWarning` instead of
:exc:`PendingDeprecationWarning`.
* The following modules have had missing APIs added to their :attr:`__all__`
attributes to match the documented APIs:
:mod:`calendar`, :mod:`cgi`, :mod:`csv`,
:mod:`~xml.etree.ElementTree`, :mod:`enum`,
:mod:`fileinput`, :mod:`ftplib`, :mod:`logging`, :mod:`mailbox`,
:mod:`mimetypes`, :mod:`optparse`, :mod:`plistlib`, :mod:`smtpd`,
:mod:`subprocess`, :mod:`tarfile`, :mod:`threading` and
:mod:`wave`. This means they will export new symbols when ``import *``
is used.
(Contributed by Joel Taddei and Jacek Kołodziej in :issue:`23883`.)
* When performing a relative import, if ``__package__`` does not compare equal
to ``__spec__.parent`` then :exc:`ImportWarning` is raised.
(Contributed by Brett Cannon in :issue:`25791`.)
* When a relative import is performed and no parent package is known, then
:exc:`ImportError` will be raised. Previously, :exc:`SystemError` could be
raised. (Contributed by Brett Cannon in :issue:`18018`.)
* Servers based on the :mod:`socketserver` module, including those
defined in :mod:`http.server`, :mod:`xmlrpc.server` and
:mod:`wsgiref.simple_server`, now only catch exceptions derived
from :exc:`Exception`. Therefore if a request handler raises
an exception like :exc:`SystemExit` or :exc:`KeyboardInterrupt`,
:meth:`~socketserver.BaseServer.handle_error` is no longer called, and
the exception will stop a single-threaded server. (Contributed by
Martin Panter in :issue:`23430`.)
* :func:`spwd.getspnam` now raises a :exc:`PermissionError` instead of
:exc:`KeyError` if the user doesn't have privileges.
* The :meth:`socket.socket.close` method now raises an exception if
an error (e.g. ``EBADF``) was reported by the underlying system call.
(Contributed by Martin Panter in :issue:`26685`.)
* The *decode_data* argument for the :class:`smtpd.SMTPChannel` and
:class:`smtpd.SMTPServer` constructors is now ``False`` by default.
This means that the argument passed to
:meth:`~smtpd.SMTPServer.process_message` is now a bytes object by
default, and ``process_message()`` will be passed keyword arguments.
Code that has already been updated in accordance with the deprecation
warning generated by 3.5 will not be affected.
* All optional arguments of the :func:`~json.dump`, :func:`~json.dumps`,
:func:`~json.load` and :func:`~json.loads` functions and
:class:`~json.JSONEncoder` and :class:`~json.JSONDecoder` class
constructors in the :mod:`json` module are now :ref:`keyword-only
<keyword-only_parameter>`.
(Contributed by Serhiy Storchaka in :issue:`18726`.)
* Subclasses of :class:`type` which don't override ``type.__new__`` may no
longer use the one-argument form to get the type of an object.
* As part of :pep:`487`, the handling of keyword arguments passed to
:class:`type` (other than the metaclass hint, ``metaclass``) is now
consistently delegated to :meth:`object.__init_subclass__`. This means that
:meth:`type.__new__` and :meth:`type.__init__` both now accept arbitrary
keyword arguments, but :meth:`object.__init_subclass__` (which is called from
:meth:`type.__new__`) will reject them by default. Custom metaclasses
accepting additional keyword arguments will need to adjust their calls to
:meth:`type.__new__` (whether direct or via :class:`super`) accordingly.
* In :class:`distutils.command.sdist.sdist`, the ``default_format``
attribute has been removed and is no longer honored. Instead, the
gzipped tarfile format is the default on all platforms and no
platform-specific selection is made.
In environments where distributions are
built on Windows and zip distributions are required, configure
the project with a ``setup.cfg`` file containing the following:
.. code-block:: ini
[sdist]
formats=zip
This behavior has also been backported to earlier Python versions
by Setuptools 26.0.0.
* In the :mod:`urllib.request` module and the
:meth:`http.client.HTTPConnection.request` method, if no Content-Length
header field has been specified and the request body is a file object,
it is now sent with HTTP 1.1 chunked encoding. If a file object has to
be sent to a HTTP 1.0 server, the Content-Length value now has to be
specified by the caller.
(Contributed by Demian Brecht and Rolf Krahl with tweaks from
Martin Panter in :issue:`12319`.)
* The :class:`~csv.DictReader` now returns rows of type
:class:`~collections.OrderedDict`.
(Contributed by Steve Holden in :issue:`27842`.)
* The :const:`crypt.METHOD_CRYPT` will no longer be added to ``crypt.methods``
if unsupported by the platform.
(Contributed by Victor Stinner in :issue:`25287`.)
* The *verbose* and *rename* arguments for
:func:`~collections.namedtuple` are now keyword-only.
(Contributed by Raymond Hettinger in :issue:`25628`.)
* On Linux, :func:`ctypes.util.find_library` now looks in
``LD_LIBRARY_PATH`` for shared libraries.
(Contributed by Vinay Sajip in :issue:`9998`.)
* The :class:`imaplib.IMAP4` class now handles flags containing the
``']'`` character in messages sent from the server to improve
real-world compatibility.
(Contributed by Lita Cho in :issue:`21815`.)
* The :func:`mmap.write() <mmap.write>` function now returns the number
of bytes written like other write methods.
(Contributed by Jakub Stasiak in :issue:`26335`.)
* The :func:`pkgutil.iter_modules` and :func:`pkgutil.walk_packages`
functions now return :class:`~pkgutil.ModuleInfo` named tuples.
(Contributed by Ramchandra Apte in :issue:`17211`.)
* :func:`re.sub` now raises an error for invalid numerical group
references in replacement templates even if the pattern is not
found in the string. The error message for invalid group references
now includes the group index and the position of the reference.
(Contributed by SilentGhost, Serhiy Storchaka in :issue:`25953`.)
* :class:`zipfile.ZipFile` will now raise :exc:`NotImplementedError` for
unrecognized compression values. Previously a plain :exc:`RuntimeError`
was raised. Additionally, calling :class:`~zipfile.ZipFile` methods
on a closed ZipFile or calling the :meth:`~zipfile.ZipFile.write` method
on a ZipFile created with mode ``'r'`` will raise a :exc:`ValueError`.
Previously, a :exc:`RuntimeError` was raised in those scenarios.
* when custom metaclasses are combined with zero-argument :func:`super` or
direct references from methods to the implicit ``__class__`` closure
variable, the implicit ``__classcell__`` namespace entry must now be passed
up to ``type.__new__`` for initialisation. Failing to do so will result in
a :exc:`DeprecationWarning` in Python 3.6 and a :exc:`RuntimeError` in
Python 3.8.
* With the introduction of :exc:`ModuleNotFoundError`, import system consumers
may start expecting import system replacements to raise that more specific
exception when appropriate, rather than the less-specific :exc:`ImportError`.
To provide future compatibility with such consumers, implementors of
alternative import systems that completely replace :func:`__import__` will
need to update their implementations to raise the new subclass when a module
can't be found at all. Implementors of compliant plugins to the default
import system shouldn't need to make any changes, as the default import
system will raise the new subclass when appropriate.
Changes in the C API
--------------------
* The :c:func:`PyMem_Malloc` allocator family now uses the :ref:`pymalloc allocator
<pymalloc>` rather than the system :c:func:`malloc`. Applications calling
:c:func:`PyMem_Malloc` without holding the GIL can now crash. Set the
:envvar:`PYTHONMALLOC` environment variable to ``debug`` to validate the
usage of memory allocators in your application. See :issue:`26249`.
* :c:func:`Py_Exit` (and the main interpreter) now override the exit status
with 120 if flushing buffered data failed. See :issue:`5319`.
CPython bytecode changes
------------------------
There have been several major changes to the :term:`bytecode` in Python 3.6.
* The Python interpreter now uses a 16-bit wordcode instead of bytecode.
(Contributed by Demur Rumed with input and reviews from
Serhiy Storchaka and Victor Stinner in :issue:`26647` and :issue:`28050`.)
* The new :opcode:`FORMAT_VALUE` and :opcode:`BUILD_STRING` opcodes as part
of the :ref:`formatted string literal <whatsnew36-pep498>` implementation.
(Contributed by Eric Smith in :issue:`25483` and
Serhiy Storchaka in :issue:`27078`.)
* The new :opcode:`BUILD_CONST_KEY_MAP` opcode to optimize the creation
of dictionaries with constant keys.
(Contributed by Serhiy Storchaka in :issue:`27140`.)
* The function call opcodes have been heavily reworked for better performance
and simpler implementation.
The :opcode:`MAKE_FUNCTION`, :opcode:`CALL_FUNCTION`,
:opcode:`CALL_FUNCTION_KW` and :opcode:`BUILD_MAP_UNPACK_WITH_CALL` opcodes
have been modified, the new :opcode:`CALL_FUNCTION_EX` and
:opcode:`BUILD_TUPLE_UNPACK_WITH_CALL` have been added, and
``CALL_FUNCTION_VAR``, ``CALL_FUNCTION_VAR_KW`` and ``MAKE_CLOSURE`` opcodes
have been removed.
(Contributed by Demur Rumed in :issue:`27095`, and Serhiy Storchaka in
:issue:`27213`, :issue:`28257`.)
* The new :opcode:`SETUP_ANNOTATIONS` and :opcode:`STORE_ANNOTATION` opcodes
have been added to support the new :term:`variable annotation` syntax.
(Contributed by Ivan Levkivskyi in :issue:`27985`.)
Notable changes in Python 3.6.2
===============================
New ``make regen-all`` build target
-----------------------------------
To simplify cross-compilation, and to ensure that CPython can reliably be
compiled without requiring an existing version of Python to already be
available, the autotools-based build system no longer attempts to implicitly
recompile generated files based on file modification times.
Instead, a new ``make regen-all`` command has been added to force regeneration
of these files when desired (e.g. after an initial version of Python has
already been built based on the pregenerated versions).
More selective regeneration targets are also defined - see
:source:`Makefile.pre.in` for details.
(Contributed by Victor Stinner in :issue:`23404`.)
.. versionadded:: 3.6.2
Removal of ``make touch`` build target
--------------------------------------
The ``make touch`` build target previously used to request implicit regeneration
of generated files by updating their modification times has been removed.
It has been replaced by the new ``make regen-all`` target.
(Contributed by Victor Stinner in :issue:`23404`.)
.. versionchanged:: 3.6.2
Notable changes in Python 3.6.4
===============================
The ``PyExc_RecursionErrorInst`` singleton that was part of the public API
has been removed as its members being never cleared may cause a segfault
during finalization of the interpreter.
(Contributed by Xavier de Gaye in :issue:`22898` and :issue:`30697`.)
Notable changes in Python 3.6.5
===============================
The :func:`locale.localeconv` function now sets temporarily the ``LC_CTYPE``
locale to the ``LC_NUMERIC`` locale in some cases.
(Contributed by Victor Stinner in :issue:`31900`.)
Notable changes in Python 3.6.7
===============================
In 3.6.7 the :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token
when provided with input that does not have a trailing new line. This behavior
now matches what the C tokenizer does internally.
(Contributed by Ammar Askar in :issue:`33899`.)