kbe/src/lib/python/Doc/whatsnew/3.7.rst
What's New In Python 3.7
:Editor: Elvis Pranskevichus [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 Git log when researching a change.
This article explains the new features in Python 3.7, compared to 3.6.
Python 3.7 was released on June 27, 2018.
For full details, see the :ref:changelog <changelog>.
.. This section singles out the most important changes in Python 3.7. Brevity is key.
New syntax features:
PEP 563 <whatsnew37-pep563>, postponed evaluation of type annotations.Backwards incompatible syntax changes:
async and :keyword:await are now reserved keywords.New library modules:
contextvars: :ref:PEP 567 -- Context Variables <whatsnew37-pep567>dataclasses: :ref:PEP 557 -- Data Classes <whatsnew37-pep557>whatsnew37_importlib_resourcesNew built-in features:
PEP 553 <whatsnew37-pep553>, the new :func:breakpoint function.Python data model improvements:
:ref:PEP 562 <whatsnew37-pep562>, customization of access to
module attributes.
:ref:PEP 560 <whatsnew37-pep560>, core support for typing module and
generic types.
the insertion-order preservation nature of :ref:dict <typesmapping>
objects has been declared_ to be an official
part of the Python language spec.
.. _has been declared: https://mail.python.org/pipermail/python-dev/2017-December/151283.html
Significant improvements in the standard library:
The :mod:asyncio module has received new features, significant
:ref:usability and performance improvements <whatsnew37_asyncio>.
The :mod:time module gained support for
:ref:functions with nanosecond resolution <whatsnew37-pep564>.
CPython implementation improvements:
Avoiding the use of ASCII as a default text encoding:
PEP 538 <whatsnew37-pep538>, legacy C locale coercionPEP 540 <whatsnew37-pep540>, forced UTF-8 runtime mode:ref:PEP 552 <whatsnew37-pep552>, deterministic .pycs
:ref:the new development runtime mode <whatsnew37-devmode>
:ref:PEP 565 <whatsnew37-pep565>, improved :exc:DeprecationWarning
handling
C API improvements:
PEP 539 <whatsnew37-pep539>, new C API for thread-local storageDocumentation improvements:
PEP 545 <whatsnew37-pep545>, Python documentation translationsJapanese <https://docs.python.org/ja/>,
French <https://docs.python.org/fr/>, and
Korean <https://docs.python.org/ko/>_.This release features notable performance improvements in many areas.
The :ref:whatsnew37-perf section lists them in detail.
For a list of changes that may affect compatibility with previous Python
releases please refer to the :ref:porting-to-python-37 section.
.. _whatsnew37-pep563:
The advent of type hints in Python uncovered two glaring usability issues
with the functionality of annotations added in :pep:3107 and refined
further in :pep:526:
annotations could only use names which were already available in the current scope, in other words they didn't support forward references of any kind; and
annotating source code had adverse effects on startup time of Python programs.
Both of these issues are fixed by postponing the evaluation of
annotations. Instead of compiling code which executes expressions in
annotations at their definition time, the compiler stores the annotation
in a string form equivalent to the AST of the expression in question.
If needed, annotations can be resolved at runtime using
:func:typing.get_type_hints. In the common case where this is not
required, the annotations are cheaper to store (since short strings
are interned by the interpreter) and make startup time faster.
Usability-wise, annotations now support forward references, making the following syntax valid::
class C:
@classmethod
def from_string(cls, source: str) -> C:
...
def validate_b(self, obj: B) -> bool:
...
class B:
...
Since this change breaks compatibility, the new behavior needs to be enabled
on a per-module basis in Python 3.7 using a :mod:__future__ import::
from __future__ import annotations
It will become the default in Python 4.0.
.. seealso::
:pep:`563` -- Postponed evaluation of annotations
PEP written and implemented by Łukasz Langa.
.. _whatsnew37-pep538:
An ongoing challenge within the Python 3 series has been determining a sensible default strategy for handling the "7-bit ASCII" text encoding assumption currently implied by the use of the default C or POSIX locale on non-Windows platforms.
:pep:538 updates the default interpreter command line interface to
automatically coerce that locale to an available UTF-8 based locale as
described in the documentation of the new :envvar:PYTHONCOERCECLOCALE
environment variable. Automatically setting LC_CTYPE this way means that
both the core interpreter and locale-aware C extensions (such as
:mod:readline) will assume the use of UTF-8 as the default text encoding,
rather than ASCII.
The platform support definition in :pep:11 has also been updated to limit
full text handling support to suitably configured non-ASCII based locales.
As part of this change, the default error handler for :data:~sys.stdin and
:data:~sys.stdout is now surrogateescape (rather than strict) when
using any of the defined coercion target locales (currently C.UTF-8,
C.utf8, and UTF-8). The default error handler for :data:~sys.stderr
continues to be backslashreplace, regardless of locale.
Locale coercion is silent by default, but to assist in debugging potentially
locale related integration problems, explicit warnings (emitted directly on
:data:~sys.stderr) can be requested by setting PYTHONCOERCECLOCALE=warn.
This setting will also cause the Python runtime to emit a warning if the
legacy C locale remains active when the core interpreter is initialized.
While :pep:538's locale coercion has the benefit of also affecting extension
modules (such as GNU readline), as well as child processes (including those
running non-Python applications and older versions of Python), it has the
downside of requiring that a suitable target locale be present on the running
system. To better handle the case where no suitable target locale is available
(as occurs on RHEL/CentOS 7, for example), Python 3.7 also implements
:ref:whatsnew37-pep540.
.. seealso::
:pep:`538` -- Coercing the legacy C locale to a UTF-8 based locale
PEP written and implemented by Nick Coghlan.
.. _whatsnew37-pep540:
The new :option:-X utf8 command line option and :envvar:PYTHONUTF8
environment variable can be used to enable the CPython UTF-8 mode.
When in UTF-8 mode, CPython ignores the locale settings, and uses the
UTF-8 encoding by default. The error handlers for :data:sys.stdin and
:data:sys.stdout streams are set to surrogateescape.
The forced UTF-8 mode can be used to change the text handling behavior in an embedded Python interpreter without changing the locale settings of an embedding application.
While :pep:540's UTF-8 mode has the benefit of working regardless of which
locales are available on the running system, it has the downside of having no
effect on extension modules (such as GNU readline), child processes running
non-Python applications, and child processes running older versions of Python.
To reduce the risk of corrupting text data when communicating with such
components, Python 3.7 also implements :ref:whatsnew37-pep540).
The UTF-8 mode is enabled by default when the locale is C or POSIX, and
the :pep:538 locale coercion feature fails to change it to a UTF-8 based
alternative (whether that failure is due to PYTHONCOERCECLOCALE=0 being set,
LC_ALL being set, or the lack of a suitable target locale).
.. seealso::
:pep:`540` -- Add a new UTF-8 mode
PEP written and implemented by Victor Stinner
.. _whatsnew37-pep553:
breakpoint()Python 3.7 includes the new built-in :func:breakpoint function as
an easy and consistent way to enter the Python debugger.
Built-in breakpoint() calls :func:sys.breakpointhook. By default, the
latter imports :mod:pdb and then calls pdb.set_trace(), but by binding
sys.breakpointhook() to the function of your choosing, breakpoint() can
enter any debugger. Additionally, the environment variable
:envvar:PYTHONBREAKPOINT can be set to the callable of your debugger of
choice. Set PYTHONBREAKPOINT=0 to completely disable built-in
breakpoint().
.. seealso::
:pep:`553` -- Built-in breakpoint()
PEP written and implemented by Barry Warsaw
.. _whatsnew37-pep539:
While Python provides a C API for thread-local storage support; the existing
:ref:Thread Local Storage (TLS) API <thread-local-storage-api> has used
:c:type:int to represent TLS keys across all platforms. This has not
generally been a problem for officially-support platforms, but that is neither
POSIX-compliant, nor portable in any practical sense.
:pep:539 changes this by providing a new :ref:Thread Specific Storage (TSS) API <thread-specific-storage-api> to CPython which supersedes use of the
existing TLS API within the CPython interpreter, while deprecating the existing
API. The TSS API uses a new type :c:type:Py_tss_t instead of :c:type:int
to represent TSS keys--an opaque type the definition of which may depend on
the underlying TLS implementation. Therefore, this will allow to build CPython
on platforms where the native TLS key is defined in a way that cannot be safely
cast to :c:type:int.
Note that on platforms where the native TLS key is defined in a way that cannot
be safely cast to :c:type:int, all functions of the existing TLS API will be
no-op and immediately return failure. This indicates clearly that the old API
is not supported on platforms where it cannot be used reliably, and that no
effort will be made to add such support.
.. seealso::
:pep:`539` -- A New C-API for Thread-Local Storage in CPython
PEP written by Erik M. Bray; implementation by Masayuki Yamamoto.
.. _whatsnew37-pep562:
Python 3.7 allows defining :meth:__getattr__ on modules and will call
it whenever a module attribute is otherwise not found. Defining
:meth:__dir__ on modules is now also allowed.
A typical example of where this may be useful is module attribute deprecation and lazy loading.
.. seealso::
:pep:`562` -- Module ``__getattr__`` and ``__dir__``
PEP written and implemented by Ivan Levkivskyi
.. _whatsnew37-pep564:
The resolution of clocks in modern systems can exceed the limited precision
of a floating point number returned by the :func:time.time function
and its variants. To avoid loss of precision, :pep:564 adds six new
"nanosecond" variants of the existing timer functions to the :mod:time
module:
time.clock_gettime_nstime.clock_settime_nstime.monotonic_nstime.perf_counter_nstime.process_time_nstime.time_nsThe new functions return the number of nanoseconds as an integer value.
Measurements <https://www.python.org/dev/peps/pep-0564/#annex-clocks-resolution-in-python>_
show that on Linux and Windows the resolution of :func:time.time_ns is
approximately 3 times better than that of :func:time.time.
.. seealso::
:pep:`564` -- Add new time functions with nanosecond resolution
PEP written and implemented by Victor Stinner
.. _whatsnew37-pep565:
__main__The default handling of :exc:DeprecationWarning has been changed such that
these warnings are once more shown by default, but only when the code
triggering them is running directly in the :mod:__main__ module. As a result,
developers of single file scripts and those using Python interactively should
once again start seeing deprecation warnings for the APIs they use, but
deprecation warnings triggered by imported application, library and framework
modules will continue to be hidden by default.
As a result of this change, the standard library now allows developers to choose between three different deprecation warning behaviours:
FutureWarning: always displayed by default, recommended for warnings
intended to be seen by application end users (e.g. for deprecated application
configuration settings).DeprecationWarning: displayed by default only in :mod:__main__ and when
running tests, recommended for warnings intended to be seen by other Python
developers where a version upgrade may result in changed behaviour or an
error.PendingDeprecationWarning: displayed by default only when running
tests, intended for cases where a future version upgrade will change the
warning category to :exc:DeprecationWarning or :exc:FutureWarning.Previously both :exc:DeprecationWarning and :exc:PendingDeprecationWarning
were only visible when running tests, which meant that developers primarily
writing single file scripts or using Python interactively could be surprised
by breaking changes in the APIs they used.
.. seealso::
:pep:`565` -- Show DeprecationWarning in ``__main__``
PEP written and implemented by Nick Coghlan
.. _whatsnew37-pep560:
typing module and Generic TypesInitially :pep:484 was designed in such way that it would not introduce any
changes to the core CPython interpreter. Now type hints and the :mod:typing
module are extensively used by the community, so this restriction is removed.
The PEP introduces two special methods :meth:__class_getitem__ and
__mro_entries__, these methods are now used by most classes and special
constructs in :mod:typing. As a result, the speed of various operations
with types increased up to 7 times, the generic types can be used without
metaclass conflicts, and several long standing bugs in :mod:typing module are
fixed.
.. seealso::
:pep:560 -- Core support for typing module and generic types
PEP written and implemented by Ivan Levkivskyi
.. _whatsnew37-pep552:
Python has traditionally checked the up-to-dateness of bytecode cache files
(i.e., .pyc files) by comparing the source metadata (last-modified timestamp
and size) with source metadata saved in the cache file header when it was
generated. While effective, this invalidation method has its drawbacks. When
filesystem timestamps are too coarse, Python can miss source updates, leading to
user confusion. Additionally, having a timestamp in the cache file is
problematic for build reproducibility <https://reproducible-builds.org/>_ and
content-based build systems.
:pep:552 extends the pyc format to allow the hash of the source file to be
used for invalidation instead of the source timestamp. Such .pyc files are
called "hash-based". By default, Python still uses timestamp-based invalidation
and does not generate hash-based .pyc files at runtime. Hash-based .pyc
files may be generated with :mod:py_compile or :mod:compileall.
Hash-based .pyc files come in two variants: checked and unchecked. Python
validates checked hash-based .pyc files against the corresponding source
files at runtime but doesn't do so for unchecked hash-based pycs. Unchecked
hash-based .pyc files are a useful performance optimization for environments
where a system external to Python (e.g., the build system) is responsible for
keeping .pyc files up-to-date.
See :ref:pyc-invalidation for more information.
.. seealso::
:pep:552 -- Deterministic pycs
PEP written and implemented by Benjamin Peterson
.. _whatsnew37-pep545:
:pep:545 describes the process of creating and maintaining Python
documentation translations.
Three new translations have been added:
.. seealso::
:pep:545 -- Python Documentation Translations
PEP written and implemented by Julien Palard, Inada Naoki, and
Victor Stinner.
.. _whatsnew37-devmode:
The new :option:-X dev command line option or the new
:envvar:PYTHONDEVMODE environment variable can be used to enable
CPython's development mode. When in development mode, CPython performs
additional runtime checks that are too expensive to be enabled by default.
See :option:-X dev documentation for the full description of the effects
of this mode.
More than 255 arguments can now be passed to a function, and a function can
now have more than 255 parameters. (Contributed by Serhiy Storchaka in
:issue:12844 and :issue:18896.)
:meth:bytes.fromhex and :meth:bytearray.fromhex now ignore all ASCII
whitespace, not only spaces. (Contributed by Robert Xiao in :issue:28927.)
:class:str, :class:bytes, and :class:bytearray gained support for
the new :meth:isascii() <str.isascii> method, which can be used to
test if a string or bytes contain only the ASCII characters.
(Contributed by INADA Naoki in :issue:32677.)
:exc:ImportError now displays module name and module __file__ path when
from ... import ... fails. (Contributed by Matthias Bussonnier in
:issue:29546.)
Circular imports involving absolute imports with binding a submodule to
a name are now supported.
(Contributed by Serhiy Storchaka in :issue:30024.)
object.__format__(x, '') is now equivalent to str(x) rather than
format(str(self), '').
(Contributed by Serhiy Storchaka in :issue:28974.)
In order to better support dynamic creation of stack traces,
:class:types.TracebackType can now be instantiated from Python code, and
the tb_next attribute on :ref:tracebacks <traceback-objects> is now
writable.
(Contributed by Nathaniel J. Smith in :issue:30579.)
When using the :option:-m switch, sys.path[0] is now eagerly expanded
to the full starting directory path, rather than being left as the empty
directory (which allows imports from the current working directory at the
time when an import occurs)
(Contributed by Nick Coghlan in :issue:33053.)
The new :option:-X importtime option or the
:envvar:PYTHONPROFILEIMPORTTIME environment variable can be used to show
the timing of each module import.
(Contributed by Victor Stinner in :issue:31415.)
.. _whatsnew37-pep567:
The new :mod:contextvars module and a set of
:ref:new C APIs <contextvarsobjects> introduce
support for context variables. Context variables are conceptually
similar to thread-local variables. Unlike TLS, context variables
support asynchronous code correctly.
The :mod:asyncio and :mod:decimal modules have been updated to use
and support context variables out of the box. Particularly the active
decimal context is now stored in a context variable, which allows
decimal operations to work with the correct context in asynchronous code.
.. seealso::
:pep:`567` -- Context Variables
PEP written and implemented by Yury Selivanov
.. _whatsnew37-pep557:
The new :func:~dataclasses.dataclass decorator provides a way to declare
data classes. A data class describes its attributes using class variable
annotations. Its constructor and other magic methods, such as
:meth:~object.__repr__, :meth:~object.__eq__, and
:meth:~object.__hash__ are generated automatically.
Example::
@dataclass
class Point:
x: float
y: float
z: float = 0.0
p = Point(1.5, 2.5)
print(p) # produces "Point(x=1.5, y=2.5, z=0.0)"
.. seealso::
:pep:`557` -- Data Classes
PEP written and implemented by Eric V. Smith
.. _whatsnew37_importlib_resources:
The new :mod:importlib.resources module provides several new APIs and one
new ABC for access to, opening, and reading resources inside packages.
Resources are roughly similar to files inside packages, but they needn't
be actual files on the physical file system. Module loaders can provide a
:meth:get_resource_reader() function which returns
a :class:importlib.abc.ResourceReader instance to support this
new API. Built-in file path loaders and zip file loaders both support this.
Contributed by Barry Warsaw and Brett Cannon in :issue:32248.
.. seealso::
`importlib_resources <http://importlib-resources.readthedocs.io/en/latest/>`_
-- a PyPI backport for earlier Python versions.
The new :meth:ArgumentParser.parse_intermixed_args() <argparse.ArgumentParser.parse_intermixed_args>
method allows intermixing options and positional arguments.
(Contributed by paul.j3 in :issue:14191.)
.. _whatsnew37_asyncio:
The :mod:asyncio module has received many new features, usability and
:ref:performance improvements <whatsnew37-asyncio-perf>. Notable changes
include:
The new :term:provisional <provisional api> :func:asyncio.run function can
be used to run a coroutine from synchronous code by automatically creating and
destroying the event loop.
(Contributed by Yury Selivanov in :issue:32314.)
asyncio gained support for :mod:contextvars.
:meth:loop.call_soon() <asyncio.loop.call_soon>,
:meth:loop.call_soon_threadsafe() <asyncio.loop.call_soon_threadsafe>,
:meth:loop.call_later() <asyncio.loop.call_later>,
:meth:loop.call_at() <asyncio.loop.call_at>, and
:meth:Future.add_done_callback() <asyncio.Future.add_done_callback>
have a new optional keyword-only context parameter.
:class:Tasks <asyncio.Task> now track their context automatically.
See :pep:567 for more details.
(Contributed by Yury Selivanov in :issue:32436.)
The new :func:asyncio.create_task function has been added as a shortcut
to asyncio.get_event_loop().create_task().
(Contributed by Andrew Svetlov in :issue:32311.)
The new :meth:loop.start_tls() <asyncio.loop.start_tls>
method can be used to upgrade an existing connection to TLS.
(Contributed by Yury Selivanov in :issue:23749.)
The new :meth:loop.sock_recv_into() <asyncio.loop.sock_recv_into>
method allows reading data from a socket directly into a provided buffer making
it possible to reduce data copies.
(Contributed by Antoine Pitrou in :issue:31819.)
The new :func:asyncio.current_task function returns the currently running
:class:~asyncio.Task instance, and the new :func:asyncio.all_tasks
function returns a set of all existing Task instances in a given loop.
The :meth:Task.current_task() <asyncio.Task.current_task> and
:meth:Task.all_tasks() <asyncio.Task.all_tasks> methods have been deprecated.
(Contributed by Andrew Svetlov in :issue:32250.)
The new provisional :class:~asyncio.BufferedProtocol class allows
implementing streaming protocols with manual control over the receive buffer.
(Contributed by Yury Selivanov in :issue:32251.)
The new :func:asyncio.get_running_loop function returns the currently
running loop, and raises a :exc:RuntimeError if no loop is running.
This is in contrast with :func:asyncio.get_event_loop, which will create
a new event loop if none is running.
(Contributed by Yury Selivanov in :issue:32269.)
The new :meth:StreamWriter.wait_closed() <asyncio.StreamWriter.wait_closed>
coroutine method allows waiting until the stream writer is closed. The new
:meth:StreamWriter.is_closing() <asyncio.StreamWriter.is_closing> method
can be used to determine if the writer is closing.
(Contributed by Andrew Svetlov in :issue:32391.)
The new :meth:loop.sock_sendfile() <asyncio.loop.sock_sendfile>
coroutine method allows sending files using :mod:os.sendfile when possible.
(Contributed by Andrew Svetlov in :issue:32410.)
The new :meth:Future.get_loop() <asyncio.Future.get_loop> and
Task.get_loop() methods return the instance of the loop on which a task or
a future were created.
:meth:Server.get_loop() <asyncio.Server.get_loop> allows doing the same for
:class:asyncio.Server objects.
(Contributed by Yury Selivanov in :issue:32415 and
Srinivas Reddy Thatiparthy in :issue:32418.)
It is now possible to control how instances of :class:asyncio.Server begin
serving. Previously, the server would start serving immediately when created.
The new start_serving keyword argument to
:meth:loop.create_server() <asyncio.loop.create_server> and
:meth:loop.create_unix_server() <asyncio.loop.create_unix_server>,
as well as :meth:Server.start_serving() <asyncio.Server.start_serving>, and
:meth:Server.serve_forever() <asyncio.Server.serve_forever>
can be used to decouple server instantiation and serving. The new
:meth:Server.is_serving() <asyncio.Server.is_serving> method returns True
if the server is serving. :class:~asyncio.Server objects are now
asynchronous context managers::
srv = await loop.create_server(...)
async with srv:
# some code
# At this point, srv is closed and no longer accepts new connections.
(Contributed by Yury Selivanov in :issue:32662.)
Callback objects returned by
:func:loop.call_later() <asyncio.loop.call_later>
gained the new :meth:when() <asyncio.TimerHandle.when> method which
returns an absolute scheduled callback timestamp.
(Contributed by Andrew Svetlov in :issue:32741.)
The :meth:loop.create_datagram_endpoint() \ <asyncio.loop.create_datagram_endpoint> method
gained support for Unix sockets.
(Contributed by Quentin Dawans in :issue:31245.)
The :func:asyncio.open_connection, :func:asyncio.start_server functions,
:meth:loop.create_connection() <asyncio.loop.create_connection>,
:meth:loop.create_server() <asyncio.loop.create_server>,
:meth:loop.create_accepted_socket() <asyncio.loop.connect_accepted_socket>
methods and their corresponding UNIX socket variants now accept the
ssl_handshake_timeout keyword argument.
(Contributed by Neil Aspinall in :issue:29970.)
The new :meth:Handle.cancelled() <asyncio.Handle.cancelled> method returns
True if the callback was cancelled.
(Contributed by Marat Sharafutdinov in :issue:31943.)
The asyncio source has been converted to use the
:keyword:async/:keyword:await syntax.
(Contributed by Andrew Svetlov in :issue:32193.)
The new :meth:ReadTransport.is_reading() <asyncio.ReadTransport.is_reading>
method can be used to determine the reading state of the transport.
Additionally, calls to
:meth:ReadTransport.resume_reading() <asyncio.ReadTransport.resume_reading>
and :meth:ReadTransport.pause_reading() <asyncio.ReadTransport.pause_reading>
are now idempotent.
(Contributed by Yury Selivanov in :issue:32356.)
Loop methods which accept socket paths now support passing
:term:path-like objects <path-like object>.
(Contributed by Yury Selivanov in :issue:32066.)
In :mod:asyncio TCP sockets on Linux are now created with TCP_NODELAY
flag set by default.
(Contributed by Yury Selivanov and Victor Stinner in :issue:27456.)
Exceptions occurring in cancelled tasks are no longer logged.
(Contributed by Yury Selivanov in :issue:30508.)
New WindowsSelectorEventLoopPolicy and
WindowsProactorEventLoopPolicy classes.
(Contributed by Yury Selivanov in :issue:33792.)
Several asyncio APIs have been
:ref:deprecated <whatsnew37-asyncio-deprecated>.
The :func:~binascii.b2a_uu function now accepts an optional backtick
keyword argument. When it's true, zeros are represented by '`'
instead of spaces. (Contributed by Xiang Zhang in :issue:30103.)
The :class:~calendar.HTMLCalendar class has new class attributes which ease
the customization of CSS classes in the produced HTML calendar.
(Contributed by Oz Tiram in :issue:30095.)
collections.namedtuple() now supports default values.
(Contributed by Raymond Hettinger in :issue:32320.)
:func:compileall.compile_dir learned the new invalidation_mode parameter,
which can be used to enable
:ref:hash-based .pyc invalidation <whatsnew37-pep552>. The invalidation
mode can also be specified on the command line using the new
--invalidation-mode argument.
(Contributed by Benjamin Peterson in :issue:31650.)
:class:ProcessPoolExecutor <concurrent.futures.ProcessPoolExecutor> and
:class:ThreadPoolExecutor <concurrent.futures.ThreadPoolExecutor> now
support the new initializer and initargs constructor arguments.
(Contributed by Antoine Pitrou in :issue:21423.)
The :class:ProcessPoolExecutor <concurrent.futures.ProcessPoolExecutor>
can now take the multiprocessing context via the new mp_context argument.
(Contributed by Thomas Moreau in :issue:31540.)
The new :func:~contextlib.nullcontext is a simpler and faster no-op
context manager than :class:~contextlib.ExitStack.
(Contributed by Jesse-Bakker in :issue:10049.)
The new :func:~contextlib.asynccontextmanager,
:class:~contextlib.AbstractAsyncContextManager, and
:class:~contextlib.AsyncExitStack have been added to
complement their synchronous counterparts. (Contributed
by Jelle Zijlstra in :issue:29679 and :issue:30241,
and by Alexander Mohr and Ilya Kulakov in :issue:29302.)
The :mod:cProfile command line now accepts -m module_name as an
alternative to script path. (Contributed by Sanyam Khurana in :issue:21862.)
The :mod:crypt module now supports the Blowfish hashing method.
(Contributed by Serhiy Storchaka in :issue:31664.)
The :func:~crypt.mksalt function now allows specifying the number of rounds
for hashing. (Contributed by Serhiy Storchaka in :issue:31702.)
The new :meth:datetime.fromisoformat() <datetime.datetime.fromisoformat>
method constructs a :class:~datetime.datetime object from a string
in one of the formats output by
:meth:datetime.isoformat() <datetime.datetime.isoformat>.
(Contributed by Paul Ganssle in :issue:15873.)
The :class:tzinfo <datetime.tzinfo> class now supports sub-minute offsets.
(Contributed by Alexander Belopolsky in :issue:5288.)
:mod:dbm.dumb now supports reading read-only files and no longer writes the
index file when it is not changed.
The :mod:decimal module now uses :ref:context variables <whatsnew37-pep567>
to store the decimal context.
(Contributed by Yury Selivanov in :issue:32630.)
The :func:~dis.dis function is now able to
disassemble nested code objects (the code of comprehensions, generator
expressions and nested functions, and the code used for building nested
classes). The maximum depth of disassembly recursion is controlled by
the new depth parameter.
(Contributed by Serhiy Storchaka in :issue:11822.)
README.rst is now included in the list of distutils standard READMEs and
therefore included in source distributions.
(Contributed by Ryan Gonzalez in :issue:11913.)
The :class:Enum <enum.Enum> learned the new _ignore_ class property,
which allows listing the names of properties which should not become
enum members.
(Contributed by Ethan Furman in :issue:31801.)
In Python 3.8, attempting to check for non-Enum objects in :class:Enum
classes will raise a :exc:TypeError (e.g. 1 in Color); similarly,
attempting to check for non-Flag objects in a :class:Flag member will
raise :exc:TypeError (e.g. 1 in Perm.RW); currently, both operations
return :const:False instead and are deprecated.
(Contributed by Ethan Furman in :issue:33217.)
:func:functools.singledispatch now supports registering implementations
using type annotations.
(Contributed by Łukasz Langa in :issue:32227.)
The new :func:gc.freeze function allows freezing all objects tracked
by the garbage collector and excluding them from future collections.
This can be used before a POSIX fork() call to make the GC copy-on-write
friendly or to speed up collection. The new :func:gc.unfreeze functions
reverses this operation. Additionally, :func:gc.get_freeze_count can
be used to obtain the number of frozen objects.
(Contributed by Li Zekun in :issue:31558.)
The :mod:hmac module now has an optimized one-shot :func:~hmac.digest
function, which is up to three times faster than :func:~hmac.HMAC.
(Contributed by Christian Heimes in :issue:32433.)
:class:~http.client.HTTPConnection and :class:~http.client.HTTPSConnection
now support the new blocksize argument for improved upload throughput.
(Contributed by Nir Soffer in :issue:31945.)
:class:~http.server.SimpleHTTPRequestHandler now supports the HTTP
If-Modified-Since header. The server returns the 304 response status if
the target file was not modified after the time specified in the header.
(Contributed by Pierre Quentel in :issue:29654.)
:class:~http.server.SimpleHTTPRequestHandler accepts the new directory
argument, in addition to the new --directory command line argument.
With this parameter, the server serves the specified directory, by default it
uses the current working directory.
(Contributed by Stéphane Wirtel and Julien Palard in :issue:28707.)
The new :class:ThreadingHTTPServer <http.server.ThreadingHTTPServer> class
uses threads to handle requests using :class:~socketserver.ThreadingMixin.
It is used when http.server is run with -m.
(Contributed by Julien Palard in :issue:31639.)
Multiple fixes for autocompletion. (Contributed by Louie Lu in :issue:15786.)
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 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.)
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.)
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.)
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 3.7.1:
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.)
The changes above have been backported to 3.6 maintenance releases.
The :class:importlib.abc.ResourceReader ABC was introduced to
support the loading of resources from packages. See also
:ref:whatsnew37_importlib_resources.
(Contributed by Barry Warsaw, Brett Cannon in :issue:32248.)
:func:importlib.reload now raises :exc:ModuleNotFoundError if the module
lacks a spec.
(Contributed by Garvit Khatri in :issue:29851.)
:func:importlib.find_spec now raises :exc:ModuleNotFoundError instead of
:exc:AttributeError if the specified parent module is not a package (i.e.
lacks a __path__ attribute).
(Contributed by Milan Oberkirch in :issue:30436.)
The new :func:importlib.source_hash can be used to compute the hash of
the passed source. A :ref:hash-based .pyc file <whatsnew37-pep552>
embeds the value returned by this function.
The new :meth:TextIOWrapper.reconfigure() <io.TextIOWrapper.reconfigure>
method can be used to reconfigure the text stream with the new settings.
(Contributed by Antoine Pitrou in :issue:30526 and
INADA Naoki in :issue:15216.)
The new subnet_of() and supernet_of() methods of
:class:ipaddress.IPv6Network and :class:ipaddress.IPv4Network can
be used for network containment tests.
(Contributed by Michel Albert and Cheryl Sabella in :issue:20825.)
:func:itertools.islice now accepts
:meth:integer-like objects <object.__index__> as start, stop,
and slice arguments.
(Contributed by Will Roberts in :issue:30537.)
The new monetary argument to :func:locale.format_string can be used
to make the conversion use monetary thousands separators and
grouping strings. (Contributed by Garvit in :issue:10379.)
The :func:locale.getpreferredencoding function now always returns 'UTF-8'
on Android or when in the :ref:forced UTF-8 mode <whatsnew37-pep540>.
:class:~logging.Logger instances can now be pickled.
(Contributed by Vinay Sajip in :issue:30520.)
The new :meth:StreamHandler.setStream() <logging.StreamHandler.setStream>
method can be used to replace the logger stream after handler creation.
(Contributed by Vinay Sajip in :issue:30522.)
It is now possible to specify keyword arguments to handler constructors in
configuration passed to :func:logging.config.fileConfig.
(Contributed by Preston Landers in :issue:31080.)
The new :func:math.remainder function implements the IEEE 754-style remainder
operation. (Contributed by Mark Dickinson in :issue:29962.)
The MIME type of .bmp has been changed from 'image/x-ms-bmp' to
'image/bmp'.
(Contributed by Nitish Chandra in :issue:22589.)
The new :meth:Database.Close() <msilib.Database.Close> method can be used
to close the :abbr:MSI database.
(Contributed by Berker Peksag in :issue:20486.)
The new :meth:Process.close() <multiprocessing.Process.close> method
explicitly closes the process object and releases all resources associated
with it. :exc:ValueError is raised if the underlying process is still
running.
(Contributed by Antoine Pitrou in :issue:30596.)
The new :meth:Process.kill() <multiprocessing.Process.kill> method can
be used to terminate the process using the :data:SIGKILL signal on Unix.
(Contributed by Vitor Pereira in :issue:30794.)
Non-daemonic threads created by :class:~multiprocessing.Process are now
joined on process exit.
(Contributed by Antoine Pitrou in :issue:18966.)
:func:os.fwalk now accepts the path argument as :class:bytes.
(Contributed by Serhiy Storchaka in :issue:28682.)
:func:os.scandir gained support for :ref:file descriptors <path_fd>.
(Contributed by Serhiy Storchaka in :issue:25996.)
The new :func:~os.register_at_fork function allows registering Python
callbacks to be executed at process fork.
(Contributed by Antoine Pitrou in :issue:16500.)
Added :func:os.preadv (combine the functionality of :func:os.readv and
:func:os.pread) and :func:os.pwritev functions (combine the functionality
of :func:os.writev and :func:os.pwrite). (Contributed by Pablo Galindo in
:issue:31368.)
The mode argument of :func:os.makedirs no longer affects the file
permission bits of newly-created intermediate-level directories.
(Contributed by Serhiy Storchaka in :issue:19930.)
:func:os.dup2 now returns the new file descriptor. Previously, None
was always returned.
(Contributed by Benjamin Peterson in :issue:32441.)
The structure returned by :func:os.stat now contains the
:attr:~os.stat_result.st_fstype attribute on Solaris and its derivatives.
(Contributed by Jesús Cea Avión in :issue:32659.)
The new :meth:Path.is_mount() <pathlib.Path.is_mount> method is now available
on POSIX systems and can be used to determine whether a path is a mount point.
(Contributed by Cooper Ry Lees in :issue:30897.)
:func:pdb.set_trace now takes an optional header keyword-only
argument. If given, it is printed to the console just before debugging
begins. (Contributed by Barry Warsaw in :issue:31389.)
:mod:pdb command line now accepts -m module_name as an alternative to
script file. (Contributed by Mario Corchero in :issue:32206.)
:func:py_compile.compile -- and by extension, :mod:compileall -- now
respects the :envvar:SOURCE_DATE_EPOCH environment variable by
unconditionally creating .pyc files for hash-based validation.
This allows for guaranteeing
reproducible builds <https://reproducible-builds.org/>_ of .pyc
files when they are created eagerly. (Contributed by Bernhard M. Wiedemann
in :issue:29708.)
The pydoc server can now bind to an arbitrary hostname specified by the
new -n command-line argument.
(Contributed by Feanil Patel in :issue:31128.)
The new :class:~queue.SimpleQueue class is an unbounded :abbr:FIFO queue.
(Contributed by Antoine Pitrou in :issue:14976.)
The flags :const:re.ASCII, :const:re.LOCALE and :const:re.UNICODE
can be set within the scope of a group.
(Contributed by Serhiy Storchaka in :issue:31690.)
:func:re.split now supports splitting on a pattern like r'\b',
'^$' or (?=-) that matches an empty string.
(Contributed by Serhiy Storchaka in :issue:25054.)
Regular expressions compiled with the :const:re.LOCALE flag no longer
depend on the locale at compile time. Locale settings are applied only
when the compiled regular expression is used.
(Contributed by Serhiy Storchaka in :issue:30215.)
:exc:FutureWarning is now emitted if a regular expression contains
character set constructs that will change semantically in the future,
such as nested sets and set operations.
(Contributed by Serhiy Storchaka in :issue:30349.)
Compiled regular expression and match objects can now be copied
using :func:copy.copy and :func:copy.deepcopy.
(Contributed by Serhiy Storchaka in :issue:10076.)
The new warn_on_full_buffer argument to the :func:signal.set_wakeup_fd
function makes it possible to specify whether Python prints a warning on
stderr when the wakeup buffer overflows.
(Contributed by Nathaniel J. Smith in :issue:30050.)
The new :func:socket.getblocking() <socket.socket.getblocking> method
returns True if the socket is in blocking mode and False otherwise.
(Contributed by Yury Selivanov in :issue:32373.)
The new :func:socket.close function closes the passed socket file descriptor.
This function should be used instead of :func:os.close for better
compatibility across platforms.
(Contributed by Christian Heimes in :issue:32454.)
The :mod:socket module now exposes the :data:socket.TCP_CONGESTION
(Linux 2.6.13), :data:socket.TCP_USER_TIMEOUT (Linux 2.6.37), and
:data:socket.TCP_NOTSENT_LOWAT (Linux 3.12) constants.
(Contributed by Omar Sandoval in :issue:26273 and
Nathaniel J. Smith in :issue:29728.)
Support for :data:socket.AF_VSOCK sockets has been added to allow
communication between virtual machines and their hosts.
(Contributed by Cathy Avery in :issue:27584.)
Sockets now auto-detect family, type and protocol from file descriptor
by default.
(Contributed by Christian Heimes in :issue:28134.)
:meth:socketserver.ThreadingMixIn.server_close now waits until all non-daemon
threads complete. :meth:socketserver.ForkingMixIn.server_close now waits
until all child processes complete.
Add a new :attr:socketserver.ForkingMixIn.block_on_close class attribute to
:class:socketserver.ForkingMixIn and :class:socketserver.ThreadingMixIn
classes. Set the class attribute to False to get the pre-3.7 behaviour.
:class:sqlite3.Connection now exposes the :meth:~sqlite3.Connection.backup
method when the underlying SQLite library is at version 3.6.11 or higher.
(Contributed by Lele Gaifax in :issue:27645.)
The database argument of :func:sqlite3.connect now accepts any
:term:path-like object, instead of just a string.
(Contributed by Anders Lorentsen in :issue:31843.)
The :mod:ssl module now uses OpenSSL's builtin API instead of
:func:~ssl.match_hostname to check a host name or an IP address. Values
are validated during TLS handshake. Any certificate validation error
including failing the host name check now raises
:exc:~ssl.SSLCertVerificationError and aborts the handshake with a proper
TLS Alert message. The new exception contains additional information.
Host name validation can be customized with
:attr:SSLContext.host_flags <ssl.SSLContext.host_flags>.
(Contributed by Christian Heimes in :issue:31399.)
.. note::
The improved host name check requires a libssl implementation compatible
with OpenSSL 1.0.2 or 1.1. Consequently, OpenSSL 0.9.8 and 1.0.1 are no
longer supported (see :ref:37-platform-support-removals for more details).
The ssl module is mostly compatible with LibreSSL 2.7.2 and newer.
The ssl module no longer sends IP addresses in SNI TLS extension.
(Contributed by Christian Heimes in :issue:32185.)
:func:~ssl.match_hostname no longer supports partial wildcards like
www*.example.org. :attr:SSLContext.host_flags <ssl.SSLContext.host_flags>
has partial wildcard matching disabled by default.
(Contributed by Mandeep Singh in :issue:23033 and Christian Heimes in
:issue:31399.)
The default cipher suite selection of the ssl module now uses a blacklist
approach rather than a hard-coded whitelist. Python no longer re-enables
ciphers that have been blocked by OpenSSL security updates. Default cipher
suite selection can be configured at compile time.
(Contributed by Christian Heimes in :issue:31429.)
Validation of server certificates containing internationalized domain names
(IDNs) is now supported. As part of this change, the
:attr:SSLSocket.server_hostname <ssl.SSLSocket.server_hostname> attribute
now stores the expected hostname in A-label form ("xn--pythn-mua.org"),
rather than the U-label form ("pythön.org"). (Contributed by
Nathaniel J. Smith and Christian Heimes in :issue:28414.)
The ssl module has preliminary and experimental support for TLS 1.3 and
OpenSSL 1.1.1. At the time of Python 3.7.0 release, OpenSSL 1.1.1 is still
under development and TLS 1.3 hasn't been finalized yet. The TLS 1.3
handshake and protocol behaves slightly differently than TLS 1.2 and earlier,
see :ref:ssl-tlsv1_3.
(Contributed by Christian Heimes in :issue:32947, :issue:20995,
:issue:29136, :issue:30622 and :issue:33618)
:class:~ssl.SSLSocket and :class:~ssl.SSLObject no longer have a public
constructor. Direct instantiation was never a documented and supported
feature. Instances must be created with :class:~ssl.SSLContext methods
:meth:~ssl.SSLContext.wrap_socket and :meth:~ssl.SSLContext.wrap_bio.
(Contributed by Christian Heimes in :issue:32951)
OpenSSL 1.1 APIs for setting the minimum and maximum TLS protocol version are
available as :attr:SSLContext.minimum_version <ssl.SSLContext.minimum_version>
and :attr:SSLContext.maximum_version <ssl.SSLContext.maximum_version>.
Supported protocols are indicated by several new flags, such as
:data:~ssl.HAS_TLSv1_1.
(Contributed by Christian Heimes in :issue:32609.)
Added :attr:SSLContext.post_handshake_auth to enable and
:meth:ssl.SSLSocket.verify_client_post_handshake to initiate TLS 1.3
post-handshake authentication.
(Contributed by Christian Heimes in :issue:34670.)
:class:string.Template now lets you to optionally modify the regular
expression pattern for braced placeholders and non-braced placeholders
separately. (Contributed by Barry Warsaw in :issue:1198569.)
The :func:subprocess.run function accepts the new capture_output
keyword argument. When true, stdout and stderr will be captured.
This is equivalent to passing :data:subprocess.PIPE as stdout and
stderr arguments.
(Contributed by Bo Bayles in :issue:32102.)
The subprocess.run function and the :class:subprocess.Popen constructor
now accept the text keyword argument as an alias
to universal_newlines.
(Contributed by Andrew Clegg in :issue:31756.)
On Windows the default for close_fds was changed from False to
True when redirecting the standard handles. It's now possible to set
close_fds to true when redirecting the standard handles. See
:class:subprocess.Popen. This means that close_fds now defaults to
True on all supported platforms.
(Contributed by Segev Finer in :issue:19764.)
The subprocess module is now more graceful when handling
:exc:KeyboardInterrupt during :func:subprocess.call,
:func:subprocess.run, or in a :class:~subprocess.Popen
context manager. It now waits a short amount of time for the child
to exit, before continuing the handling of the KeyboardInterrupt
exception.
(Contributed by Gregory P. Smith in :issue:25942.)
The new :func:sys.breakpointhook hook function is called by the
built-in :func:breakpoint.
(Contributed by Barry Warsaw in :issue:31353.)
On Android, the new :func:sys.getandroidapilevel returns the build-time
Android API version.
(Contributed by Victor Stinner in :issue:28740.)
The new :func:sys.get_coroutine_origin_tracking_depth function returns
the current coroutine origin tracking depth, as set by
the new :func:sys.set_coroutine_origin_tracking_depth. :mod:asyncio
has been converted to use this new API instead of
the deprecated :func:sys.set_coroutine_wrapper.
(Contributed by Nathaniel J. Smith in :issue:32591.)
:pep:564 adds six new functions with nanosecond resolution to the
:mod:time module:
time.clock_gettime_nstime.clock_settime_nstime.monotonic_nstime.perf_counter_nstime.process_time_nstime.time_nsNew clock identifiers have been added:
time.CLOCK_BOOTTIME (Linux): Identical to
:data:time.CLOCK_MONOTONIC, except it also includes any time that the
system is suspended.time.CLOCK_PROF (FreeBSD, NetBSD and OpenBSD): High-resolution
per-process CPU timer.time.CLOCK_UPTIME (FreeBSD, OpenBSD): Time whose absolute value is
the time the system has been running and not suspended, providing accurate
uptime measurement.The new :func:time.thread_time and :func:time.thread_time_ns functions
can be used to get per-thread CPU time measurements.
(Contributed by Antoine Pitrou in :issue:32025.)
The new :func:time.pthread_getcpuclockid function returns the clock ID
of the thread-specific CPU-time clock.
The new :class:tkinter.ttk.Spinbox class is now available.
(Contributed by Alan Moore in :issue:32585.)
:class:tracemalloc.Traceback behaves more like regular tracebacks,
sorting the frames from oldest to most recent.
:meth:Traceback.format() <tracemalloc.Traceback.format>
now accepts negative limit, truncating the result to the
abs(limit) oldest frames. To get the old behaviour, use
the new most_recent_first argument to Traceback.format().
(Contributed by Jesse Bakker in :issue:32121.)
The new :class:~types.WrapperDescriptorType,
:class:~types.MethodWrapperType, :class:~types.MethodDescriptorType,
and :class:~types.ClassMethodDescriptorType classes are now available.
(Contributed by Manuel Krebber and Guido van Rossum in :issue:29377,
and Serhiy Storchaka in :issue:32265.)
The new :func:types.resolve_bases function resolves MRO entries
dynamically as specified by :pep:560.
(Contributed by Ivan Levkivskyi in :issue:32717.)
The internal :mod:unicodedata database has been upgraded to use Unicode 11 <http://www.unicode.org/versions/Unicode11.0.0/>_. (Contributed by Benjamin
Peterson.)
The new -k command-line option allows filtering tests by a name
substring or a Unix shell-like pattern.
For example, python -m unittest -k foo runs
foo_tests.SomeTest.test_something, bar_tests.SomeTest.test_foo,
but not bar_tests.FooTest.test_something.
(Contributed by Jonas Haag in :issue:32071.)
The :const:~unittest.mock.sentinel attributes now preserve their identity
when they are :mod:copied <copy> or :mod:pickled <pickle>. (Contributed by
Serhiy Storchaka in :issue:20804.)
The new :func:~unittest.mock.seal function allows sealing
:class:~unittest.mock.Mock instances, which will disallow further creation
of attribute mocks. The seal is applied recursively to all attributes that
are themselves mocks.
(Contributed by Mario Corchero in :issue:30541.)
:func:urllib.parse.quote has been updated from :rfc:2396 to :rfc:3986,
adding ~ to the set of characters that are never quoted by default.
(Contributed by Christian Theune and Ratnadeep Debnath in :issue:16285.)
The :func:uu.encode function now accepts an optional backtick
keyword argument. When it's true, zeros are represented by '`'
instead of spaces. (Contributed by Xiang Zhang in :issue:30103.)
The new :attr:UUID.is_safe <uuid.UUID.is_safe> attribute relays information
from the platform about whether generated UUIDs are generated with a
multiprocessing-safe method.
(Contributed by Barry Warsaw in :issue:22807.)
:func:uuid.getnode now prefers universally administered
MAC addresses over locally administered MAC addresses.
This makes a better guarantee for global uniqueness of UUIDs returned
from :func:uuid.uuid1. If only locally administered MAC addresses are
available, the first such one found is returned.
(Contributed by Barry Warsaw in :issue:32107.)
The initialization of the default warnings filters has changed as follows:
warnings enabled via command line options (including those for :option:-b
and the new CPython-specific :option:-X dev option) are always passed
to the warnings machinery via the :data:sys.warnoptions attribute.
warnings filters enabled via the command line or the environment now have the following order of precedence:
BytesWarning filter for :option:-b (or -bb)-W optionPYTHONWARNINGS environment
variabledefault filter added
for the new -X dev mode)in CPython debug builds, all warnings are now displayed by default (the implicit filter list is empty)
(Contributed by Nick Coghlan and Victor Stinner in :issue:20361,
:issue:32043, and :issue:32230.)
Deprecation warnings are once again shown by default in single-file scripts and
at the interactive prompt. See :ref:whatsnew37-pep565 for details.
(Contributed by Nick Coghlan in :issue:31975.)
As mitigation against DTD and external entity retrieval, the
:mod:xml.dom.minidom and :mod:xml.sax modules no longer process
external entities by default.
(Contributed by Christian Heimes in :issue:17239.)
:ref:ElementPath <elementtree-xpath> predicates in the :meth:find
methods can now compare text of the current node with [. = "text"],
not only text in children. Predicates also allow adding spaces for
better readability. (Contributed by Stefan Behnel in :issue:31648.)
:meth:SimpleXMLRPCDispatcher.register_function <xmlrpc.server.SimpleXMLRPCDispatcher>
can now be used as a decorator. (Contributed by Xiang Zhang in
:issue:7769.)
Function :func:~zipapp.create_archive now accepts an optional filter
argument to allow the user to select which files should be included in the
archive. (Contributed by Irmen de Jong in :issue:31072.)
Function :func:~zipapp.create_archive now accepts an optional compressed
argument to generate a compressed archive. A command line option
--compress has also been added to support compression.
(Contributed by Zhiming Wang in :issue:31638.)
:class:~zipfile.ZipFile now accepts the new compresslevel parameter to
control the compression level.
(Contributed by Bo Bayles in :issue:21417.)
Subdirectories in archives created by ZipFile are now stored in
alphabetical order.
(Contributed by Bernhard M. Wiedemann in :issue:30693.)
A new API for thread-local storage has been implemented. See
:ref:whatsnew37-pep539 for an overview and
:ref:thread-specific-storage-api for a complete reference.
(Contributed by Masayuki Yamamoto in :issue:25658.)
The new :ref:context variables <whatsnew37-pep567> functionality
exposes a number of :ref:new C APIs <contextvarsobjects>.
The new :c:func:PyImport_GetModule function returns the previously
imported module with the given name.
(Contributed by Eric Snow in :issue:28411.)
The new :c:macro:Py_RETURN_RICHCOMPARE macro eases writing rich
comparison functions.
(Contributed by Petr Victorin in :issue:23699.)
The new :c:macro:Py_UNREACHABLE macro can be used to mark unreachable
code paths.
(Contributed by Barry Warsaw in :issue:31338.)
The :mod:tracemalloc now exposes a C API through the new
:c:func:PyTraceMalloc_Track and :c:func:PyTraceMalloc_Untrack
functions.
(Contributed by Victor Stinner in :issue:30054.)
The new :c:func:import__find__load__start and
:c:func:import__find__load__done static markers can be used to trace
module imports.
(Contributed by Christian Heimes in :issue:31574.)
The fields :c:member:name and :c:member:doc of structures
:c:type:PyMemberDef, :c:type:PyGetSetDef,
:c:type:PyStructSequence_Field, :c:type:PyStructSequence_Desc,
and :c:type:wrapperbase are now of type const char * rather of
char *. (Contributed by Serhiy Storchaka in :issue:28761.)
The result of :c:func:PyUnicode_AsUTF8AndSize and :c:func:PyUnicode_AsUTF8
is now of type const char * rather of char *. (Contributed by Serhiy
Storchaka in :issue:28769.)
The result of :c:func:PyMapping_Keys, :c:func:PyMapping_Values and
:c:func:PyMapping_Items is now always a list, rather than a list or a
tuple. (Contributed by Oren Milman in :issue:28280.)
Added functions :c:func:PySlice_Unpack and :c:func:PySlice_AdjustIndices.
(Contributed by Serhiy Storchaka in :issue:27867.)
:c:func:PyOS_AfterFork is deprecated in favour of the new functions
:c:func:PyOS_BeforeFork, :c:func:PyOS_AfterFork_Parent and
:c:func:PyOS_AfterFork_Child. (Contributed by Antoine Pitrou in
:issue:16500.)
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.
Added C API support for timezones with timezone constructors
:c:func:PyTimeZone_FromOffset and :c:func:PyTimeZone_FromOffsetAndName,
and access to the UTC singleton with :c:data:PyDateTime_TimeZone_UTC.
Contributed by Paul Ganssle in :issue:10381.
The type of results of :c:func:PyThread_start_new_thread and
:c:func:PyThread_get_thread_ident, and the id parameter of
:c:func:PyThreadState_SetAsyncExc changed from :c:type:long to
:c:type:unsigned long.
(Contributed by Serhiy Storchaka in :issue:6532.)
:c:func:PyUnicode_AsWideCharString now raises a :exc:ValueError if the
second argument is NULL and the :c:type:wchar_t* string contains null
characters. (Contributed by Serhiy Storchaka in :issue:30708.)
Changes to the startup sequence and the management of dynamic memory
allocators mean that the long documented requirement to call
:c:func:Py_Initialize before calling most C API functions is now
relied on more heavily, and failing to abide by it may lead to segfaults in
embedding applications. See the :ref:porting-to-python-37 section in this
document and the :ref:pre-init-safe section in the C API documentation
for more details.
The new :c:func:PyInterpreterState_GetID returns the unique ID for a
given interpreter.
(Contributed by Eric Snow in :issue:29102.)
:c:func:Py_DecodeLocale, :c:func:Py_EncodeLocale now use the UTF-8
encoding when the :ref:UTF-8 mode <whatsnew37-pep540> is enabled.
(Contributed by Victor Stinner in :issue:29240.)
:c:func:PyUnicode_DecodeLocaleAndSize and :c:func:PyUnicode_EncodeLocale
now use the current locale encoding for surrogateescape error handler.
(Contributed by Victor Stinner in :issue:29240.)
The start and end parameters of :c:func:PyUnicode_FindChar are
now adjusted to behave like string slices.
(Contributed by Xiang Zhang in :issue:28822.)
Support for building --without-threads has been removed. The
:mod:threading module is now always available.
(Contributed by Antoine Pitrou in :issue:31370.).
A full copy of libffi is no longer bundled for use when building the
:mod:_ctypes <ctypes> module on non-OSX UNIX platforms. An installed copy
of libffi is now required when building _ctypes on such platforms.
(Contributed by Zachary Ware in :issue:27979.)
The Windows build process no longer depends on Subversion to pull in external
sources, a Python script is used to download zipfiles from GitHub instead.
If Python 3.6 is not found on the system (via py -3.6), NuGet is used to
download a copy of 32-bit Python for this purpose. (Contributed by Zachary
Ware in :issue:30450.)
The :mod:ssl module requires OpenSSL 1.0.2 or 1.1 compatible libssl.
OpenSSL 1.0.1 has reached end of lifetime on 2016-12-31 and is no longer
supported. LibreSSL is temporarily not supported as well. LibreSSL releases
up to version 2.6.4 are missing required OpenSSL 1.0.2 APIs.
.. _whatsnew37-perf:
The overhead of calling many methods of various standard library classes
implemented in C has been significantly reduced by porting more code
to use the METH_FASTCALL convention.
(Contributed by Victor Stinner in :issue:29300, :issue:29507,
:issue:29452, and :issue:29286.)
Various optimizations have reduced Python startup time by 10% on Linux and
up to 30% on macOS.
(Contributed by Victor Stinner, INADA Naoki in :issue:29585, and
Ivan Levkivskyi in :issue:31333.)
Method calls are now up to 20% faster due to the bytecode changes which
avoid creating bound method instances.
(Contributed by Yury Selivanov and INADA Naoki in :issue:26110.)
.. _whatsnew37-asyncio-perf:
The :mod:asyncio module received a number of notable optimizations for
commonly used functions:
The :func:asyncio.get_event_loop function has been reimplemented in C to
make it up to 15 times faster.
(Contributed by Yury Selivanov in :issue:32296.)
:class:asyncio.Future callback management has been optimized.
(Contributed by Yury Selivanov in :issue:32348.)
:func:asyncio.gather is now up to 15% faster.
(Contributed by Yury Selivanov in :issue:32355.)
:func:asyncio.sleep is now up to 2 times faster when the delay
argument is zero or negative.
(Contributed by Andrew Svetlov in :issue:32351.)
The performance overhead of asyncio debug mode has been reduced.
(Contributed by Antoine Pitrou in :issue:31970.)
As a result of :ref:PEP 560 work <whatsnew37-pep560>, the import time
of :mod:typing has been reduced by a factor of 7, and many typing operations
are now faster.
(Contributed by Ivan Levkivskyi in :issue:32226.)
:func:sorted and :meth:list.sort have been optimized for common cases
to be up to 40-75% faster.
(Contributed by Elliot Gorokhovsky in :issue:28685.)
:meth:dict.copy is now up to 5.5 times faster.
(Contributed by Yury Selivanov in :issue:31179.)
:func:hasattr and :func:getattr are now about 4 times faster when
name is not found and obj does not override :meth:object.__getattr__
or :meth:object.__getattribute__.
(Contributed by INADA Naoki in :issue:32544.)
Searching for certain Unicode characters (like Ukrainian capital "Є")
in a string was up to 25 times slower than searching for other characters.
It is now only 3 times slower in the worst case.
(Contributed by Serhiy Storchaka in :issue:24821.)
The :func:collections.namedtuple factory has been reimplemented to
make the creation of named tuples 4 to 6 times faster.
(Contributed by Jelle Zijlstra with further improvements by INADA Naoki,
Serhiy Storchaka, and Raymond Hettinger in :issue:28638.)
:meth:date.fromordinal and :meth:date.fromtimestamp are now up to
30% faster in the common case.
(Contributed by Paul Ganssle in :issue:32403.)
The :func:os.fwalk function is now up to 2 times faster thanks to
the use of :func:os.scandir.
(Contributed by Serhiy Storchaka in :issue:25996.)
The speed of the :func:shutil.rmtree function has been improved by
20--40% thanks to the use of the :func:os.scandir function.
(Contributed by Serhiy Storchaka in :issue:28564.)
Optimized case-insensitive matching and searching of :mod:regular expressions <re>. Searching some patterns can now be up to 20 times faster.
(Contributed by Serhiy Storchaka in :issue:30285.)
:func:re.compile now converts flags parameter to int object if
it is RegexFlag. It is now as fast as Python 3.5, and faster than
Python 3.6 by about 10% depending on the pattern.
(Contributed by INADA Naoki in :issue:31671.)
The :meth:~selectors.BaseSelector.modify methods of classes
:class:selectors.EpollSelector, :class:selectors.PollSelector
and :class:selectors.DevpollSelector may be around 10% faster under
heavy loads. (Contributed by Giampaolo Rodola' in :issue:30014)
Constant folding has been moved from the peephole optimizer to the new AST
optimizer, which is able perform optimizations more consistently.
(Contributed by Eugene Toder and INADA Naoki in :issue:29469 and
:issue:11549.)
Most functions and methods in :mod:abc have been rewritten in C.
This makes creation of abstract base classes, and calling :func:isinstance
and :func:issubclass on them 1.5x faster. This also reduces Python
start-up time by up to 10%. (Contributed by Ivan Levkivskyi and INADA Naoki
in :issue:31333)
Significant speed improvements to alternate constructors for
:class:datetime.date and :class:datetime.datetime by using fast-path
constructors when not constructing subclasses. (Contributed by Paul Ganssle
in :issue:32403)
The speed of comparison of :class:array.array instances has been
improved considerably in certain cases. It is now from 10x to 70x faster
when comparing arrays holding values of the same integer type.
(Contributed by Adrian Wielgosik in :issue:24700.)
The :func:math.erf and :func:math.erfc functions now use the (faster)
C library implementation on most platforms.
(Contributed by Serhiy Storchaka in :issue:26121.)
Trace hooks may now opt out of receiving the line and opt into receiving
the opcode events from the interpreter by setting the corresponding new
f_trace_lines and f_trace_opcodes attributes on the
frame being traced. (Contributed by Nick Coghlan in :issue:31344.)
Fixed some consistency problems with namespace package module attributes.
Namespace module objects now have an __file__ that is set to None
(previously unset), and their __spec__.origin is also set to None
(previously the string "namespace"). See :issue:32305. Also, the
namespace module object's __spec__.loader is set to the same value as
__loader__ (previously, the former was set to None). See
:issue:32303.
The :func:locals dictionary now displays in the lexical order that
variables were defined. Previously, the order was undefined.
(Contributed by Raymond Hettinger in :issue:32690.)
The :mod:distutils upload command no longer tries to change CR
end-of-line characters to CRLF. This fixes a corruption issue with sdists
that ended with a byte equivalent to CR.
(Contributed by Bo Bayles in :issue:32304.)
Yield expressions (both yield and yield from clauses) are now deprecated
in comprehensions and generator expressions (aside from the iterable expression
in the leftmost :keyword:!for clause). This ensures that comprehensions
always immediately return a container of the appropriate type (rather than
potentially returning a :term:generator iterator object), while generator
expressions won't attempt to interleave their implicit output with the output
from any explicit yield expressions. In Python 3.7, such expressions emit
:exc:DeprecationWarning when compiled, in Python 3.8 this will be a
:exc:SyntaxError.
(Contributed by Serhiy Storchaka in :issue:10544.)
Returning a subclass of :class:complex from :meth:object.__complex__ is
deprecated and will be an error in future Python versions. This makes
__complex__() consistent with :meth:object.__int__ and
:meth:object.__float__.
(Contributed by Serhiy Storchaka in :issue:28894.)
:func:aifc.openfp has been deprecated and will be removed in Python 3.9.
Use :func:aifc.open instead.
(Contributed by Brian Curtin in :issue:31985.)
.. _whatsnew37-asyncio-deprecated:
Support for directly await-ing instances of :class:asyncio.Lock and
other asyncio synchronization primitives has been deprecated. An
asynchronous context manager must be used in order to acquire and release
the synchronization resource.
(Contributed by Andrew Svetlov in :issue:32253.)
The :meth:asyncio.Task.current_task and :meth:asyncio.Task.all_tasks
methods have been deprecated.
(Contributed by Andrew Svetlov in :issue:32250.)
In Python 3.8, the abstract base classes in :mod:collections.abc will no
longer be exposed in the regular :mod:collections module. This will help
create a clearer distinction between the concrete classes and the abstract
base classes.
(Contributed by Serhiy Storchaka in :issue:25988.)
:mod:dbm.dumb now supports reading read-only files and no longer writes the
index file when it is not changed. A deprecation warning is now emitted
if the index file is missing and recreated in the 'r' and 'w'
modes (this will be an error in future Python releases).
(Contributed by Serhiy Storchaka in :issue:28847.)
In Python 3.8, attempting to check for non-Enum objects in :class:Enum
classes will raise a :exc:TypeError (e.g. 1 in Color); similarly,
attempting to check for non-Flag objects in a :class:Flag member will
raise :exc:TypeError (e.g. 1 in Perm.RW); currently, both operations
return :const:False instead.
(Contributed by Ethan Furman in :issue:33217.)
Using non-integer value for selecting a plural form in :mod:gettext is
now deprecated. It never correctly worked. (Contributed by Serhiy Storchaka
in :issue:28692.)
Methods
:meth:MetaPathFinder.find_module() <importlib.abc.MetaPathFinder.find_module>
(replaced by
:meth:MetaPathFinder.find_spec() <importlib.abc.MetaPathFinder.find_spec>)
and
:meth:PathEntryFinder.find_loader() <importlib.abc.PathEntryFinder.find_loader>
(replaced by
:meth:PathEntryFinder.find_spec() <importlib.abc.PathEntryFinder.find_spec>)
both deprecated in Python 3.4 now emit :exc:DeprecationWarning.
(Contributed by Matthias Bussonnier in :issue:29576)
The :class:importlib.abc.ResourceLoader ABC has been deprecated in
favour of :class:importlib.abc.ResourceReader.
:func:locale.format has been deprecated, use :meth:locale.format_string
instead. (Contributed by Garvit in :issue:10379.)
The :mod:macpath is now deprecated and will be removed in Python 3.8.
(Contributed by Chi Hsuan Yen in :issue:9850.)
:mod:dummy_threading and :mod:_dummy_thread have been deprecated. It is
no longer possible to build Python with threading disabled.
Use :mod:threading instead.
(Contributed by Antoine Pitrou in :issue:31370.)
The silent argument value truncation in :func:socket.htons and
:func:socket.ntohs has been deprecated. In future versions of Python,
if the passed argument is larger than 16 bits, an exception will be raised.
(Contributed by Oren Milman in :issue:28332.)
:func:ssl.wrap_socket is deprecated. Use
:meth:ssl.SSLContext.wrap_socket instead.
(Contributed by Christian Heimes in :issue:28124.)
:func:sunau.openfp has been deprecated and will be removed in Python 3.9.
Use :func:sunau.open instead.
(Contributed by Brian Curtin in :issue:31985.)
Deprecated :func:sys.set_coroutine_wrapper and
:func:sys.get_coroutine_wrapper.
The undocumented sys.callstats() function has been deprecated and
will be removed in a future Python version.
(Contributed by Victor Stinner in :issue:28799.)
:func:wave.openfp has been deprecated and will be removed in Python 3.9.
Use :func:wave.open instead.
(Contributed by Brian Curtin in :issue:31985.)
Function :c:func:PySlice_GetIndicesEx is deprecated and replaced with
a macro if Py_LIMITED_API is not set or set to a value in the range
between 0x03050400 and 0x03060000 (not inclusive), or is 0x03060100
or higher. (Contributed by Serhiy Storchaka in :issue:27867.)
:c:func:PyOS_AfterFork has been deprecated. Use :c:func:PyOS_BeforeFork,
:c:func:PyOS_AfterFork_Parent or :c:func:PyOS_AfterFork_Child() instead.
(Contributed by Antoine Pitrou in :issue:16500.)
.. _37-platform-support-removals:
FreeBSD 9 and older are no longer officially supported.
For full Unicode support, including within extension modules, *nix platforms
are now expected to provide at least one of C.UTF-8 (full locale),
C.utf8 (full locale) or UTF-8 (LC_CTYPE-only locale) as an
alternative to the legacy ASCII-based C locale.
OpenSSL 0.9.8 and 1.0.1 are no longer supported, which means building CPython 3.7 with SSL/TLS support on older platforms still using these versions requires custom build options that link to a more recent version of OpenSSL.
Notably, this issue affects the Debian 8 (aka "jessie") and Ubuntu 14.04 (aka "Trusty") LTS Linux distributions, as they still use OpenSSL 1.0.1 by default.
Debian 9 ("stretch") and Ubuntu 16.04 ("xenial"), as well as recent releases of other LTS Linux releases (e.g. RHEL/CentOS 7.5, SLES 12-SP3), use OpenSSL 1.0.2 or later, and remain supported in the default build configuration.
CPython's own :source:CI configuration file <.travis.yml> provides an
example of using the SSL
:source:compatibility testing infrastructure <Tools/ssl/multissltests.py> in
CPython's test suite to build and link against OpenSSL 1.1.0 rather than an
outdated system provided OpenSSL.
The following features and APIs have been removed from Python 3.7:
The os.stat_float_times() function has been removed. It was introduced in
Python 2.3 for backward compatibility with Python 2.2, and was deprecated
since Python 3.1.
Unknown escapes consisting of '\' and an ASCII letter in replacement
templates for :func:re.sub were deprecated in Python 3.5, and will now
cause an error.
Removed support of the exclude argument in :meth:tarfile.TarFile.add.
It was deprecated in Python 2.7 and 3.2. Use the filter argument instead.
The splitunc() function in the :mod:ntpath module was deprecated in
Python 3.1, and has now been removed. Use the :func:~os.path.splitdrive
function instead.
:func:collections.namedtuple no longer supports the verbose parameter
or _source attribute which showed the generated source code for the
named tuple class. This was part of an optimization designed to speed-up
class creation. (Contributed by Jelle Zijlstra with further improvements
by INADA Naoki, Serhiy Storchaka, and Raymond Hettinger in :issue:28638.)
Functions :func:bool, :func:float, :func:list and :func:tuple no
longer take keyword arguments. The first argument of :func:int can now
be passed only as positional argument.
Removed previously deprecated in Python 2.4 classes Plist, Dict and
_InternalDict in the :mod:plistlib module. Dict values in the result
of functions :func:~plistlib.readPlist and
:func:~plistlib.readPlistFromBytes are now normal dicts. You no longer
can use attribute access to access items of these dictionaries.
The asyncio.windows_utils.socketpair() function has been
removed. Use the :func:socket.socketpair function instead,
it is available on all platforms since Python 3.5.
asyncio.windows_utils.socketpair was just an alias to
socket.socketpair on Python 3.5 and newer.
:mod:asyncio no longer exports the :mod:selectors and
:mod:_overlapped modules as asyncio.selectors and
asyncio._overlapped. Replace from asyncio import selectors with
import selectors.
Direct instantiation of :class:ssl.SSLSocket and :class:ssl.SSLObject
objects is now prohibited. The constructors were never documented, tested,
or designed as public constructors. Users were supposed to use
:func:ssl.wrap_socket or :class:ssl.SSLContext.
(Contributed by Christian Heimes in :issue:32951.)
The unused :mod:distutils install_misc command has been removed.
(Contributed by Eric N. Vander Weele in :issue:29218.)
The fpectl module has been removed. It was never enabled by
default, never worked correctly on x86-64, and it changed the Python
ABI in ways that caused unexpected breakage of C extensions.
(Contributed by Nathaniel J. Smith in :issue:29137.)
The python launcher, (py.exe), can accept 32 & 64 bit specifiers without
having to specify a minor version as well. So py -3-32 and py -3-64
become valid as well as py -3.7-32, also the -m-64 and -m.n-64 forms
are now accepted to force 64 bit python even if 32 bit would have otherwise
been used. If the specified version is not available py.exe will error exit.
(Contributed by Steve Barnes in :issue:30291.)
The launcher can be run as py -0 to produce a list of the installed pythons,
with default marked with an asterisk. Running py -0p will include the paths.
If py is run with a version specifier that cannot be matched it will also print
the short form list of available specifiers.
(Contributed by Steve Barnes in :issue:30362.)
.. _porting-to-python-37:
This section lists previously described changes and other bugfixes that may require changes to your code.
:keyword:async and :keyword:await names are now reserved keywords.
Code using these names as identifiers will now raise a :exc:SyntaxError.
(Contributed by Jelle Zijlstra in :issue:30406.)
:pep:479 is enabled for all code in Python 3.7, meaning that
:exc:StopIteration exceptions raised directly or indirectly in
coroutines and generators are transformed into :exc:RuntimeError
exceptions.
(Contributed by Yury Selivanov in :issue:32670.)
:meth:object.__aiter__ methods can no longer be declared as
asynchronous. (Contributed by Yury Selivanov in :issue:31709.)
Due to an oversight, earlier Python versions erroneously accepted the following syntax::
f(1 for x in [1],)
class C(1 for x in [1]):
pass
Python 3.7 now correctly raises a :exc:SyntaxError, as a generator
expression always needs to be directly inside a set of parentheses
and cannot have a comma on either side, and the duplication of the
parentheses can be omitted only on calls.
(Contributed by Serhiy Storchaka in :issue:32012 and :issue:32023.)
When using the :option:-m switch, the initial working directory is now added
to :data:sys.path, rather than an empty string (which dynamically denoted
the current working directory at the time of each import). Any programs that
are checking for the empty string, or otherwise relying on the previous
behaviour, will need to be updated accordingly (e.g. by also checking for
os.getcwd() or os.path.dirname(__main__.__file__), depending on why
the code was checking for the empty string in the first place).
:meth:socketserver.ThreadingMixIn.server_close now waits until all
non-daemon threads complete. Set the new
:attr:socketserver.ThreadingMixIn.block_on_close class attribute to
False to get the pre-3.7 behaviour.
(Contributed by Victor Stinner in :issue:31233 and :issue:33540.)
:meth:socketserver.ForkingMixIn.server_close now waits until all
child processes complete. Set the new
:attr:socketserver.ForkingMixIn.block_on_close class attribute to False
to get the pre-3.7 behaviour.
(Contributed by Victor Stinner in :issue:31151 and :issue:33540.)
The :func:locale.localeconv function now temporarily sets the LC_CTYPE
locale to the value of LC_NUMERIC in some cases.
(Contributed by Victor Stinner in :issue:31900.)
:meth:pkgutil.walk_packages now raises a :exc:ValueError if path is
a string. Previously an empty list was returned.
(Contributed by Sanyam Khurana in :issue:24744.)
A format string argument for :meth:string.Formatter.format
is now :ref:positional-only <positional-only_parameter>.
Passing it as a keyword argument was deprecated in Python 3.5. (Contributed
by Serhiy Storchaka in :issue:29193.)
Attributes :attr:~http.cookies.Morsel.key,
:attr:~http.cookies.Morsel.value and
:attr:~http.cookies.Morsel.coded_value of class
:class:http.cookies.Morsel are now read-only.
Assigning to them was deprecated in Python 3.5.
Use the :meth:~http.cookies.Morsel.set method for setting them.
(Contributed by Serhiy Storchaka in :issue:29192.)
The mode argument of :func:os.makedirs no longer affects the file
permission bits of newly-created intermediate-level directories.
To set their file permission bits you can set the umask before invoking
makedirs().
(Contributed by Serhiy Storchaka in :issue:19930.)
The :attr:struct.Struct.format type is now :class:str instead of
:class:bytes. (Contributed by Victor Stinner in :issue:21071.)
:func:~cgi.parse_multipart now accepts the encoding and errors
arguments and returns the same results as
:class:~FieldStorage: for non-file fields, the value associated to a key
is a list of strings, not bytes.
(Contributed by Pierre Quentel in :issue:29979.)
Due to internal changes in :mod:socket, calling :func:socket.fromshare
on a socket created by :func:socket.share <socket.socket.share> in older
Python versions is not supported.
repr for :exc:BaseException has changed to not include the trailing
comma. Most exceptions are affected by this change.
(Contributed by Serhiy Storchaka in :issue:30399.)
repr for :class:datetime.timedelta has changed to include the keyword
arguments in the output. (Contributed by Utkarsh Upadhyay in :issue:30302.)
Because :func:shutil.rmtree is now implemented using the :func:os.scandir
function, the user specified handler onerror is now called with the first
argument os.scandir instead of os.listdir when listing the directory
is failed.
Support for nested sets and set operations in regular expressions as in
Unicode Technical Standard #18_ might be added in the future. This would
change the syntax. To facilitate this future change a :exc:FutureWarning
will be raised in ambiguous cases for the time being.
That include sets starting with a literal '[' or containing literal
character sequences '--', '&&', '~~', and '||'. To
avoid a warning, escape them with a backslash.
(Contributed by Serhiy Storchaka in :issue:30349.)
.. _Unicode Technical Standard #18: https://unicode.org/reports/tr18/
The result of splitting a string on a :mod:regular expression <re>
that could match an empty string has been changed. For example
splitting on r'\s*' will now split not only on whitespaces as it
did previously, but also on empty strings before all non-whitespace
characters and just before the end of the string.
The previous behavior can be restored by changing the pattern
to r'\s+'. A :exc:FutureWarning was emitted for such patterns since
Python 3.5.
For patterns that match both empty and non-empty strings, the result of
searching for all matches may also be changed in other cases. For example
in the string 'a\n\n', the pattern r'(?m)^\s*?$' will not only
match empty strings at positions 2 and 3, but also the string '\n' at
positions 2--3. To match only blank lines, the pattern should be rewritten
as r'(?m)^[^\S\n]*$'.
:func:re.sub() now replaces empty matches adjacent to a previous
non-empty match. For example re.sub('x*', '-', 'abxd') returns now
'-a-b--d-' instead of '-a-b-d-' (the first minus between 'b' and
'd' replaces 'x', and the second minus replaces an empty string between
'x' and 'd').
(Contributed by Serhiy Storchaka in :issue:25054 and :issue:32308.)
Change :func:re.escape to only escape regex special characters instead
of escaping all characters other than ASCII letters, numbers, and '_'.
(Contributed by Serhiy Storchaka in :issue:29995.)
:class:tracemalloc.Traceback frames are now sorted from oldest to most
recent to be more consistent with :mod:traceback.
(Contributed by Jesse Bakker in :issue:32121.)
On OSes that support :const:socket.SOCK_NONBLOCK or
:const:socket.SOCK_CLOEXEC bit flags, the
:attr:socket.type <socket.socket.type> no longer has them applied.
Therefore, checks like if sock.type == socket.SOCK_STREAM
work as expected on all platforms.
(Contributed by Yury Selivanov in :issue:32331.)
On Windows the default for the close_fds argument of
:class:subprocess.Popen was changed from :const:False to :const:True
when redirecting the standard handles. If you previously depended on handles
being inherited when using :class:subprocess.Popen with standard io
redirection, you will have to pass close_fds=False to preserve the
previous behaviour, or use
:attr:STARTUPINFO.lpAttributeList <subprocess.STARTUPINFO.lpAttributeList>.
:meth:importlib.machinery.PathFinder.invalidate_caches -- which implicitly
affects :func:importlib.invalidate_caches -- now deletes entries
in :data:sys.path_importer_cache which are set to None.
(Contributed by Brett Cannon in :issue:33169.)
In :mod:asyncio,
:meth:loop.sock_recv() <asyncio.loop.sock_recv>,
:meth:loop.sock_sendall() <asyncio.loop.sock_sendall>,
:meth:loop.sock_accept() <asyncio.loop.sock_accept>,
:meth:loop.getaddrinfo() <asyncio.loop.getaddrinfo>,
:meth:loop.getnameinfo() <asyncio.loop.getnameinfo>
have been changed to be proper coroutine methods to match their
documentation. Previously, these methods returned :class:asyncio.Future
instances.
(Contributed by Yury Selivanov in :issue:32327.)
:attr:asyncio.Server.sockets now returns a copy of the internal list
of server sockets, instead of returning it directly.
(Contributed by Yury Selivanov in :issue:32662.)
:attr:Struct.format <struct.Struct.format> is now a :class:str instance
instead of a :class:bytes instance.
(Contributed by Victor Stinner in :issue:21071.)
:meth:ast.literal_eval() is now stricter. Addition and subtraction of
arbitrary numbers are no longer allowed.
(Contributed by Serhiy Storchaka in :issue:31778.)
:meth:Calendar.itermonthdates <calendar.Calendar.itermonthdates>
will now consistently raise an exception when a date falls outside of the
0001-01-01 through 9999-12-31 range. To support applications that
cannot tolerate such exceptions, the new
:meth:Calendar.itermonthdays3 <calendar.Calendar.itermonthdays3> and
:meth:Calendar.itermonthdays4 <calendar.Calendar.itermonthdays4> can be used.
The new methods return tuples and are not restricted by the range supported by
:class:datetime.date.
(Contributed by Alexander Belopolsky in :issue:28292.)
:class:collections.ChainMap now preserves the order of the underlying
mappings. (Contributed by Raymond Hettinger in :issue:32792.)
The submit() method of :class:concurrent.futures.ThreadPoolExecutor
and :class:concurrent.futures.ProcessPoolExecutor now raises
a :exc:RuntimeError if called during interpreter shutdown.
(Contributed by Mark Nemec in :issue:33097.)
The :class:configparser.ConfigParser constructor now uses read_dict()
to process the default values, making its behavior consistent with the
rest of the parser. Non-string keys and values in the defaults
dictionary are now being implicitly converted to strings.
(Contributed by James Tocknell in :issue:23835.)
Several undocumented internal imports were removed.
One example is that os.errno is no longer available; use import errno
directly instead.
Note that such undocumented internal imports may be removed any time without
notice, even in micro version releases.
The function :c:func:PySlice_GetIndicesEx is considered unsafe for
resizable sequences. If the slice indices are not instances of :class:int,
but objects that implement the :meth:!__index__ method, the sequence can be
resized after passing its length to :c:func:!PySlice_GetIndicesEx. This
can lead to returning indices out of the length of the sequence. For
avoiding possible problems use new functions :c:func:PySlice_Unpack and
:c:func:PySlice_AdjustIndices.
(Contributed by Serhiy Storchaka in :issue:27867.)
There are two new opcodes: :opcode:LOAD_METHOD and :opcode:CALL_METHOD.
(Contributed by Yury Selivanov and INADA Naoki in :issue:26110.)
The :opcode:STORE_ANNOTATION opcode has been removed.
(Contributed by Mark Shannon in :issue:32550.)
The file used to override :data:sys.path is now called
<python-executable>._pth instead of 'sys.path'.
See :ref:finding_modules for more information.
(Contributed by Steve Dower in :issue:28137.)
In preparation for potential future changes to the public CPython runtime
initialization API (see :pep:432 for an initial, but somewhat outdated,
draft), CPython's internal startup
and configuration management logic has been significantly refactored. While
these updates are intended to be entirely transparent to both embedding
applications and users of the regular CPython CLI, they're being mentioned
here as the refactoring changes the internal order of various operations
during interpreter startup, and hence may uncover previously latent defects,
either in embedding applications, or in CPython itself.
(Initially contributed by Nick Coghlan and Eric Snow as part of
:issue:22257, and further updated by Nick, Eric, and Victor Stinner in a
number of other issues). Some known details affected:
:c:func:PySys_AddWarnOptionUnicode is not currently usable by embedding
applications due to the requirement to create a Unicode object prior to
calling Py_Initialize. Use :c:func:PySys_AddWarnOption instead.
warnings filters added by an embedding application with
:c:func:PySys_AddWarnOption should now more consistently take precedence
over the default filters set by the interpreter
Due to changes in the way the default warnings filters are configured,
setting :c:data:Py_BytesWarningFlag to a value greater than one is no longer
sufficient to both emit :exc:BytesWarning messages and have them converted
to exceptions. Instead, the flag must be set (to cause the warnings to be
emitted in the first place), and an explicit error::BytesWarning
warnings filter added to convert them to exceptions.
Due to a change in the way docstrings are handled by the compiler, the
implicit return None in a function body consisting solely of a docstring
is now marked as occurring on the same line as the docstring, not on the
function's header line.
The current exception state has been moved from the frame object to the co-routine.
This simplified the interpreter and fixed a couple of obscure bugs caused by
having swap exception state when entering or exiting a generator.
(Contributed by Mark Shannon in :issue:25612.)
Starting in 3.7.1, :c:func:Py_Initialize now consistently reads and respects
all of the same environment settings as :c:func:Py_Main (in earlier Python
versions, it respected an ill-defined subset of those environment variables,
while in Python 3.7.0 it didn't read any of them due to :issue:34247). If
this behavior is unwanted, set :c:data:Py_IgnoreEnvironmentFlag to 1 before
calling :c:func:Py_Initialize.
In 3.7.1 the C API for Context Variables
:ref:was updated <contextvarsobjects_pointertype_change> to use
:c:type:PyObject pointers. See also :issue:34762.
:mod:xml.dom.minidom and :mod:xml.sax modules no longer process
external entities by default. See also :issue:17239.
In 3.7.1 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.)
In 3.7.2, :mod:venv on Windows no longer copies the original binaries, but
creates redirector scripts named python.exe and pythonw.exe instead.
This resolves a long standing issue where all virtual environments would have
to be upgraded or recreated with each Python update. However, note that this
release will still require recreation of virtual environments in order to get
the new scripts.