What’s New In Python 3.7¶
- Editor:
Elvis Pranskevichus <elvis@magic.io>
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 thechangelog.
Summary – Release Highlights¶
New syntax features:
PEP 563,postponed evaluation of type annotations.
Backwards incompatible syntax changes:
New library modules:
New built-in features:
PEP 553,the new
breakpoint()
function.
Python data model improvements:
PEP 562,customization of access to module attributes.
PEP 560,core support for typing module and generic types.
the insertion-order preservation nature ofdict objectshas been declaredto be an official part of the Python language spec.
Significant improvements in the standard library:
The
asyncio
module has received new features, significant usability and performance improvements.The
time
module gained support for functions with nanosecond resolution.
CPython implementation improvements:
Avoiding the use of ASCII as a default text encoding:
PEP 552,deterministic.pycs
PEP 565,improved
DeprecationWarning
handling
C API improvements:
PEP 539,new C API for thread-local storage
Documentation improvements:
PEP 545,Python documentation translations
This release features notable performance improvements in many areas. TheOptimizationssection lists them in detail.
For a list of changes that may affect compatibility with previous Python releases please refer to thePorting to Python 3.7section.
New Features¶
PEP 563: Postponed Evaluation of Annotations¶
The advent of type hints in Python uncovered two glaring usability issues with the functionality of annotations added inPEP 3107and refined further inPEP 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
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:
classC:
@classmethod
deffrom_string(cls,source:str)->C:
...
defvalidate_b(self,obj:B)->bool:
...
classB:
...
Since this change breaks compatibility, the new behavior needs to be enabled
on a per-module basis in Python 3.7 using a__future__
import:
from__future__importannotations
It will become the default in Python 3.10.
See also
- PEP 563– Postponed evaluation of annotations
PEP written and implemented by Łukasz Langa.
PEP 538: Legacy C Locale Coercion¶
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 538updates 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 newPYTHONCOERCECLOCALE
environment variable. Automatically settingLC_CTYPE
this way means that
both the core interpreter and locale-aware C extensions (such as
readline
) will assume the use of UTF-8 as the default text encoding,
rather than ASCII.
The platform support definition inPEP 11has 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 forstdin
and
stdout
is nowsurrogateescape
(rather thanstrict
) when
using any of the defined coercion target locales (currentlyC.UTF-8
,
C.utf8
,andUTF-8
). The default error handler forstderr
continues to bebackslashreplace
,regardless of locale.
Locale coercion is silent by default, but to assist in debugging potentially
locale related integration problems, explicit warnings (emitted directly on
stderr
) can be requested by settingPYTHONCOERCECLOCALE=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.
WhilePEP 538’s locale coercion has the benefit of also affecting extension
modules (such as GNUreadline
), 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
PEP 540: Forced UTF-8 Runtime Mode.
See also
- PEP 538– Coercing the legacy C locale to a UTF-8 based locale
PEP written and implemented by Nick Coghlan.
PEP 540: Forced UTF-8 Runtime Mode¶
The new-X
utf8
command line option andPYTHONUTF8
environment variable can be used to enable thePython UTF-8 Mode.
When in UTF-8 mode, CPython ignores the locale settings, and uses the
UTF-8 encoding by default. The error handlers forsys.stdin
and
sys.stdout
streams are set tosurrogateescape
.
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.
WhilePEP 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 GNUreadline
), 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 implementsPEP 540: Forced UTF-8 Runtime Mode).
The UTF-8 mode is enabled by default when the locale isC
orPOSIX
,and
thePEP 538locale coercion feature fails to change it to a UTF-8 based
alternative (whether that failure is due toPYTHONCOERCECLOCALE=0
being set,
LC_ALL
being set, or the lack of a suitable target locale).
See also
- PEP 540– Add a new UTF-8 mode
PEP written and implemented by Victor Stinner
PEP 553: Built-inbreakpoint()
¶
Python 3.7 includes the new built-inbreakpoint()
function as
an easy and consistent way to enter the Python debugger.
Built-inbreakpoint()
callssys.breakpointhook()
.By default, the
latter importspdb
and then callspdb.set_trace()
,but by binding
sys.breakpointhook()
to the function of your choosing,breakpoint()
can
enter any debugger. Additionally, the environment variable
PYTHONBREAKPOINT
can be set to the callable of your debugger of
choice. SetPYTHONBREAKPOINT=0
to completely disable built-in
breakpoint()
.
See also
- PEP 553– Built-in breakpoint()
PEP written and implemented by Barry Warsaw
PEP 539: New C API for Thread-Local Storage¶
While Python provides a C API for thread-local storage support; the existing Thread Local Storage (TLS) APIhas used intto 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 539changes this by providing a newThread Specific Storage (TSS)
APIto CPython which supersedes use of the
existing TLS API within the CPython interpreter, while deprecating the existing
API. The TSS API uses a new typePy_tss_t
instead ofint
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 toint.
Note that on platforms where the native TLS key is defined in a way that cannot be safely cast toint,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.
See also
- PEP 539– A New C-API for Thread-Local Storage in CPython
PEP written by Erik M. Bray; implementation by Masayuki Yamamoto.
PEP 562: Customization of Access to Module Attributes¶
Python 3.7 allows defining__getattr__()
on modules and will call
it whenever a module attribute is otherwise not found. Defining
__dir__()
on modules is now also allowed.
A typical example of where this may be useful is module attribute deprecation and lazy loading.
See also
- PEP 562– Module
__getattr__
and__dir__
PEP written and implemented by Ivan Levkivskyi
PEP 564: New Time Functions With Nanosecond Resolution¶
The resolution of clocks in modern systems can exceed the limited precision
of a floating-point number returned by thetime.time()
function
and its variants. To avoid loss of precision,PEP 564adds six new
“nanosecond” variants of the existing timer functions to thetime
module:
The new functions return the number of nanoseconds as an integer value.
Measurements
show that on Linux and Windows the resolution oftime.time_ns()
is
approximately 3 times better than that oftime.time()
.
See also
- PEP 564– Add new time functions with nanosecond resolution
PEP written and implemented by Victor Stinner
PEP 565: Show DeprecationWarning in__main__
¶
The default handling ofDeprecationWarning
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__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__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 toDeprecationWarning
orFutureWarning
.
Previously bothDeprecationWarning
andPendingDeprecationWarning
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.
See also
- PEP 565– Show DeprecationWarning in
__main__
PEP written and implemented by Nick Coghlan
PEP 560: Core Support fortyping
module and Generic Types¶
InitiallyPEP 484was designed in such way that it would not introduceany
changes to the core CPython interpreter. Now type hints and thetyping
module are extensively used by the community, so this restriction is removed.
The PEP introduces two special methods__class_getitem__()
and
__mro_entries__
,these methods are now used by most classes and special
constructs intyping
.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 intyping
module are
fixed.
See also
- PEP 560– Core support for typing module and generic types
PEP written and implemented by Ivan Levkivskyi
PEP 552: Hash-based.pyc Files¶
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 forbuild reproducibilityand
content-based build systems.
PEP 552extends 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 withpy_compile
orcompileall
.
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.
SeeCached bytecode invalidationfor more information.
See also
- PEP 552– Deterministic pycs
PEP written and implemented by Benjamin Peterson
PEP 545: Python Documentation Translations¶
PEP 545describes the process of creating and maintaining Python documentation translations.
Three new translations have been added:
Japanese:https://docs. Python.org/ja/
French:https://docs. Python.org/fr/
Korean:https://docs. Python.org/ko/
See also
- PEP 545– Python Documentation Translations
PEP written and implemented by Julien Palard, Inada Naoki, and Victor Stinner.
Python Development Mode (-X dev)¶
The new-X
dev
command line option or the new
PYTHONDEVMODE
environment variable can be used to enable
Python Development Mode.When in development mode, Python performs
additional runtime checks that are too expensive to be enabled by default.
SeePython Development Modedocumentation for the full
description.
Other Language Changes¶
An
await
expression and comprehensions containing anasyncfor
clause were illegal in the expressions in formatted string literalsdue to a problem with the implementation. In Python 3.7 this restriction was lifted.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 bpo-12844andbpo-18896.)
bytes.fromhex()
andbytearray.fromhex()
now ignore all ASCII whitespace, not only spaces. (Contributed by Robert Xiao inbpo-28927.)str
,bytes
,andbytearray
gained support for the newisascii()
method, which can be used to test if a string or bytes contain only the ASCII characters. (Contributed by INADA Naoki inbpo-32677.)ImportError
now displays module name and module__file__
path whenfrom...import...
fails. (Contributed by Matthias Bussonnier in bpo-29546.)Circular imports involving absolute imports with binding a submodule to a name are now supported. (Contributed by Serhiy Storchaka inbpo-30024.)
object.__format__(x,'')
is now equivalent tostr(x)
rather thanformat(str(self),'')
. (Contributed by Serhiy Storchaka inbpo-28974.)In order to better support dynamic creation of stack traces,
types.TracebackType
can now be instantiated from Python code, and thetb_next
attribute on tracebacksis now writable. (Contributed by Nathaniel J. Smith inbpo-30579.)When using the
-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 thecurrentworking directory at the time when an import occurs) (Contributed by Nick Coghlan inbpo-33053.)The new
-X
importtime
option or thePYTHONPROFILEIMPORTTIME
environment variable can be used to show the timing of each module import. (Contributed by Inada Naoki inbpo-31415.)
New Modules¶
contextvars¶
The newcontextvars
module and a set of
new C APIsintroduce
support forcontext variables.Context variables are conceptually
similar to thread-local variables. Unlike TLS, context variables
support asynchronous code correctly.
Theasyncio
anddecimal
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.
See also
- PEP 567– Context Variables
PEP written and implemented by Yury Selivanov
dataclasses¶
The newdataclass()
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
__repr__()
,__eq__()
,and
__hash__()
are generated automatically.
Example:
@dataclass
classPoint:
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)"
See also
- PEP 557– Data Classes
PEP written and implemented by Eric V. Smith
importlib.resources¶
The newimportlib.resources
module provides several new APIs and one
new ABC for access to, opening, and readingresourcesinside 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
get_resource_reader()
function which returns
aimportlib.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 inbpo-32248.
See also
importlib_resources – a PyPI backport for earlier Python versions.
Improved Modules¶
argparse¶
The newArgumentParser.parse_intermixed_args()
method allows intermi xing options and positional arguments.
(Contributed by paul.j3 inbpo-14191.)
asyncio¶
Theasyncio
module has received many new features, usability and
performance improvements.Notable changes
include:
The newprovisional
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 inbpo-32314.)asyncio gained support for
contextvars
.loop.call_soon()
,loop.call_soon_threadsafe()
,loop.call_later()
,loop.call_at()
,andFuture.add_done_callback()
have a new optional keyword-onlycontextparameter.Tasks
now track their context automatically. SeePEP 567for more details. (Contributed by Yury Selivanov inbpo-32436.)The new
asyncio.create_task()
function has been added as a shortcut toasyncio.get_event_loop().create_task()
. (Contributed by Andrew Svetlov inbpo-32311.)The new
loop.start_tls()
method can be used to upgrade an existing connection to TLS. (Contributed by Yury Selivanov inbpo-23749.)The new
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 inbpo-31819.)The new
asyncio.current_task()
function returns the currently runningTask
instance, and the newasyncio.all_tasks()
function returns a set of all existingTask
instances in a given loop. TheTask.current_task()
andTask.all_tasks()
methods have been deprecated. (Contributed by Andrew Svetlov inbpo-32250.)The newprovisional
BufferedProtocol
class allows implementing streaming protocols with manual control over the receive buffer. (Contributed by Yury Selivanov inbpo-32251.)The new
asyncio.get_running_loop()
function returns the currently running loop, and raises aRuntimeError
if no loop is running. This is in contrast withasyncio.get_event_loop()
,which willcreate a new event loop if none is running. (Contributed by Yury Selivanov inbpo-32269.)The new
StreamWriter.wait_closed()
coroutine method allows waiting until the stream writer is closed. The newStreamWriter.is_closing()
method can be used to determine if the writer is closing. (Contributed by Andrew Svetlov inbpo-32391.)The new
loop.sock_sendfile()
coroutine method allows sending files usingos.sendfile
when possible. (Contributed by Andrew Svetlov inbpo-32410.)The new
Future.get_loop()
andTask.get_loop()
methods return the instance of the loop on which a task or a future were created.Server.get_loop()
allows doing the same forasyncio.Server
objects. (Contributed by Yury Selivanov inbpo-32415and Srinivas Reddy Thatiparthy inbpo-32418.)It is now possible to control how instances of
asyncio.Server
begin serving. Previously, the server would start serving immediately when created. The newstart_servingkeyword argument toloop.create_server()
andloop.create_unix_server()
, as well asServer.start_serving()
,andServer.serve_forever()
can be used to decouple server instantiation and serving. The newServer.is_serving()
method returnsTrue
if the server is serving.Server
objects are now asynchronous context managers:srv=awaitloop.create_server(...) asyncwithsrv: # some code # At this point, srv is closed and no longer accepts new connections.
(Contributed by Yury Selivanov inbpo-32662.)
Callback objects returned by
loop.call_later()
gained the newwhen()
method which returns an absolute scheduled callback timestamp. (Contributed by Andrew Svetlov inbpo-32741.)The
loop.create_datagram_endpoint()
method gained support for Unix sockets. (Contributed by Quentin Dawans inbpo-31245.)The
asyncio.open_connection()
,asyncio.start_server()
functions,loop.create_connection()
,loop.create_server()
,loop.create_accepted_socket()
methods and their corresponding UNIX socket variants now accept the ssl_handshake_timeoutkeyword argument. (Contributed by Neil Aspinall inbpo-29970.)The new
Handle.cancelled()
method returnsTrue
if the callback was cancelled. (Contributed by Marat Sharafutdinov inbpo-31943.)The asyncio source has been converted to use the
async
/await
syntax. (Contributed by Andrew Svetlov inbpo-32193.)The new
ReadTransport.is_reading()
method can be used to determine the reading state of the transport. Additionally, calls toReadTransport.resume_reading()
andReadTransport.pause_reading()
are now idempotent. (Contributed by Yury Selivanov inbpo-32356.)Loop methods which accept socket paths now support passing path-like objects. (Contributed by Yury Selivanov inbpo-32066.)
In
asyncio
TCP sockets on Linux are now created withTCP_NODELAY
flag set by default. (Contributed by Yury Selivanov and Victor Stinner inbpo-27456.)Exceptions occurring in cancelled tasks are no longer logged. (Contributed by Yury Selivanov inbpo-30508.)
New
WindowsSelectorEventLoopPolicy
andWindowsProactorEventLoopPolicy
classes. (Contributed by Yury Selivanov inbpo-33792.)
Severalasyncio
APIs have been
deprecated.
binascii¶
Theb2a_uu()
function now accepts an optionalbacktick
keyword argument. When it’s true, zeros are represented by'`'
instead of spaces. (Contributed by Xiang Zhang inbpo-30103.)
calendar¶
TheHTMLCalendar
class has new class attributes which ease
the customization of CSS classes in the produced HTML calendar.
(Contributed by Oz Tiram inbpo-30095.)
collections¶
collections.namedtuple()
now supports default values.
(Contributed by Raymond Hettinger inbpo-32320.)
compileall¶
compileall pile_dir()
learned the newinvalidation_modeparameter,
which can be used to enable
hash-based.pyc invalidation.The invalidation
mode can also be specified on the command line using the new
--invalidation-mode
argument.
(Contributed by Benjamin Peterson inbpo-31650.)
concurrent.futures¶
ProcessPoolExecutor
and
ThreadPoolExecutor
now
support the newinitializerandinitargsconstructor arguments.
(Contributed by Antoine Pitrou inbpo-21423.)
TheProcessPoolExecutor
can now take the multiprocessing context via the newmp_contextargument.
(Contributed by Thomas Moreau inbpo-31540.)
contextlib¶
The newnullcontext()
is a simpler and faster no-op
context manager thanExitStack
.
(Contributed by Jesse-Bakker inbpo-10049.)
The newasynccontextmanager()
,
AbstractAsyncContextManager
,and
AsyncExitStack
have been added to
complement their synchronous counterparts. (Contributed
by Jelle Zijlstra inbpo-29679andbpo-30241,
and by Alexander Mohr and Ilya Kulakov inbpo-29302.)
cProfile¶
ThecProfile
command line now accepts-mmodule_name
as an
alternative to script path. (Contributed by Sanyam Khurana inbpo-21862.)
crypt¶
Thecrypt
module now supports the Blowfish hashing method.
(Contributed by Serhiy Storchaka inbpo-31664.)
Themksalt()
function now allows specifying the number of rounds
for hashing. (Contributed by Serhiy Storchaka inbpo-31702.)
datetime¶
The newdatetime.fromisoformat()
method constructs adatetime
object from a string
in one of the formats output by
datetime.isoformat()
.
(Contributed by Paul Ganssle inbpo-15873.)
Thetzinfo
class now supports sub-minute offsets.
(Contributed by Alexander Belopolsky inbpo-5288.)
dbm¶
dbm.dumb
now supports reading read-only files and no longer writes the
index file when it is not changed.
decimal¶
Thedecimal
module now usescontext variables
to store the decimal context.
(Contributed by Yury Selivanov inbpo-32630.)
dis¶
Thedis()
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 newdepthparameter.
(Contributed by Serhiy Storchaka inbpo-11822.)
distutils¶
README.rst
is now included in the list of distutils standard READMEs and
therefore included in source distributions.
(Contributed by Ryan Gonzalez inbpo-11913.)
enum¶
TheEnum
learned the new_ignore_
class property,
which allows listing the names of properties which should not become
enum members.
(Contributed by Ethan Furman inbpo-31801.)
In Python 3.8, attempting to check for non-Enum objects inEnum
classes will raise aTypeError
(e.g.1inColor
); similarly,
attempting to check for non-Flag objects in aFlag
member will
raiseTypeError
(e.g.1inPerm.RW
); currently, both operations
returnFalse
instead and are deprecated.
(Contributed by Ethan Furman inbpo-33217.)
functools¶
functools.singledispatch()
now supports registering implementations
using type annotations.
(Contributed by Łukasz Langa inbpo-32227.)
gc¶
The newgc.freeze()
function allows freezing all objects tracked
by the garbage collector and excluding them from future collections.
This can be used before a POSIXfork()
call to make the GC copy-on-write
friendly or to speed up collection. The newgc.unfreeze()
functions
reverses this operation. Additionally,gc.get_freeze_count()
can
be used to obtain the number of frozen objects.
(Contributed by Li Zekun inbpo-31558.)
hmac¶
Thehmac
module now has an optimized one-shotdigest()
function, which is up to three times faster thanHMAC()
.
(Contributed by Christian Heimes inbpo-32433.)
http.client¶
HTTPConnection
andHTTPSConnection
now support the newblocksizeargument for improved upload throughput.
(Contributed by Nir Soffer inbpo-31945.)
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 inbpo-29654.)
SimpleHTTPRequestHandler
accepts the newdirectory
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 inbpo-28707.)
The newThreadingHTTPServer
class
uses threads to handle requests usingThreadingMixin
.
It is used whenhttp.server
is run with-m
.
(Contributed by Julien Palard inbpo-31639.)
idlelib and IDLE¶
Multiple fixes for autocompletion. (Contributed by Louie Lu inbpo-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 inbpo-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 inbpo-13802.) The sample can be edited to include other characters. (Contributed by Serhiy Storchaka inbpo-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 inbpo-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 inbpo-33642, bpo-33768,andbpo-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 inbpo-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 inbpo-1529353.)
The changes above have been backported to 3.6 maintenance releases.
NEW in 3.7.4:
Add “Run Customized” to the Run menu to run a module with customized settings. Any command line arguments entered are added to sys.argv. They re-appear in the box for the next customized run. One can also suppress the normal Shell main module restart. (Contributed by Cheryl Sabella, Terry Jan Reedy, and others inbpo-5680andbpo-37627.)
New in 3.7.5:
Add optional line numbers for IDLE editor windows. Windows open without line numbers unless set otherwise in the General tab of the configuration dialog. Line numbers for an existing window are shown and hidden in the Options menu. (Contributed by Tal Einat and Saimadhav Heblikar inbpo-17535.)
importlib¶
Theimportlib.abc.ResourceReader
ABC was introduced to
support the loading of resources from packages. See also
importlib.resources.
(Contributed by Barry Warsaw, Brett Cannon inbpo-32248.)
importlib.reload()
now raisesModuleNotFoundError
if the module
lacks a spec.
(Contributed by Garvit Khatri inbpo-29851.)
importlib.find_spec()
now raisesModuleNotFoundError
instead of
AttributeError
if the specified parent module is not a package (i.e.
lacks a__path__
attribute).
(Contributed by Milan Oberkirch inbpo-30436.)
The newimportlib.source_hash()
can be used to compute the hash of
the passed source. Ahash-based.pyc file
embeds the value returned by this function.
io¶
The newTextIOWrapper.reconfigure()
method can be used to reconfigure the text stream with the new settings.
(Contributed by Antoine Pitrou inbpo-30526and
INADA Naoki inbpo-15216.)
ipaddress¶
The newsubnet_of()
andsupernet_of()
methods of
ipaddress.IPv6Network
andipaddress.IPv4Network
can
be used for network containment tests.
(Contributed by Michel Albert and Cheryl Sabella inbpo-20825.)
itertools¶
itertools.islice()
now accepts
integer-likeobjects
as start, stop,
and slice arguments.
(Contributed by Will Roberts inbpo-30537.)
locale¶
The newmonetaryargument tolocale.format_string()
can be used
to make the conversion use monetary thousands separators and
grouping strings. (Contributed by Garvit inbpo-10379.)
Thelocale.getpreferredencoding()
function now always returns'UTF-8'
on Android or when in theforced UTF-8 mode.
logging¶
Logger
instances can now be pickled.
(Contributed by Vinay Sajip inbpo-30520.)
The newStreamHandler.setStream()
method can be used to replace the logger stream after handler creation.
(Contributed by Vinay Sajip inbpo-30522.)
It is now possible to specify keyword arguments to handler constructors in
configuration passed tologging.config.fileConfig()
.
(Contributed by Preston Landers inbpo-31080.)
math¶
The newmath.remainder()
function implements the IEEE 754-style remainder
operation. (Contributed by Mark Dickinson inbpo-29962.)
mimetypes¶
The MIME type of.bmp has been changed from'image/x-ms-bmp'
to
'image/bmp'
.
(Contributed by Nitish Chandra inbpo-22589.)
msilib¶
The newDatabase.Close()
method can be used
to close theMSIdatabase.
(Contributed by Berker Peksag inbpo-20486.)
multiprocessing¶
The newProcess.close()
method
explicitly closes the process object and releases all resources associated
with it.ValueError
is raised if the underlying process is still
running.
(Contributed by Antoine Pitrou inbpo-30596.)
The newProcess.kill()
method can
be used to terminate the process using theSIGKILL
signal on Unix.
(Contributed by Vitor Pereira inbpo-30794.)
Non-daemonic threads created byProcess
are now
joined on process exit.
(Contributed by Antoine Pitrou inbpo-18966.)
os¶
os.fwalk()
now accepts thepathargument asbytes
.
(Contributed by Serhiy Storchaka inbpo-28682.)
os.scandir()
gained support forfile descriptors.
(Contributed by Serhiy Storchaka inbpo-25996.)
The newregister_at_fork()
function allows registering Python
callbacks to be executed at process fork.
(Contributed by Antoine Pitrou inbpo-16500.)
Addedos.preadv()
(combine the functionality ofos.readv()
and
os.pread()
) andos.pwritev()
functions (combine the functionality
ofos.writev()
andos.pwrite()
). (Contributed by Pablo Galindo in
bpo-31368.)
The mode argument ofos.makedirs()
no longer affects the file
permission bits of newly created intermediate-level directories.
(Contributed by Serhiy Storchaka inbpo-19930.)
os.dup2()
now returns the new file descriptor. Previously,None
was always returned.
(Contributed by Benjamin Peterson inbpo-32441.)
The structure returned byos.stat()
now contains the
st_fstype
attribute on Solaris and its derivatives.
(Contributed by Jesús Cea Avión inbpo-32659.)
pathlib¶
The newPath.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 inbpo-30897.)
pdb¶
pdb.set_trace()
now takes an optionalheaderkeyword-only
argument. If given, it is printed to the console just before debugging
begins. (Contributed by Barry Warsaw inbpo-31389.)
pdb
command line now accepts-mmodule_name
as an alternative to
script file. (Contributed by Mario Corchero inbpo-32206.)
py_compile¶
py_compile pile()
– and by extension,compileall
– now
respects theSOURCE_DATE_EPOCH
environment variable by
unconditionally creating.pyc
files for hash-based validation.
This allows for guaranteeing
reproducible buildsof.pyc
files when they are created eagerly. (Contributed by Bernhard M. Wiedemann
inbpo-29708.)
pydoc¶
The pydoc server can now bind to an arbitrary hostname specified by the
new-n
command-line argument.
(Contributed by Feanil Patel inbpo-31128.)
queue¶
The newSimpleQueue
class is an unboundedFIFOqueue.
(Contributed by Antoine Pitrou inbpo-14976.)
re¶
The flagsre.ASCII
,re.LOCALE
andre.UNICODE
can be set within the scope of a group.
(Contributed by Serhiy Storchaka inbpo-31690.)
re.split()
now supports splitting on a pattern liker'\b'
,
'^$'
or(?=-)
that matches an empty string.
(Contributed by Serhiy Storchaka inbpo-25054.)
Regular expressions compiled with there.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 inbpo-30215.)
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 inbpo-30349.)
Compiled regular expression and match objects can now be copied
usingcopy.copy()
andcopy.deepcopy()
.
(Contributed by Serhiy Storchaka inbpo-10076.)
signal¶
The newwarn_on_full_bufferargument to thesignal.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 inbpo-30050.)
socket¶
The newsocket.getblocking()
method
returnsTrue
if the socket is in blocking mode andFalse
otherwise.
(Contributed by Yury Selivanov inbpo-32373.)
The newsocket.close()
function closes the passed socket file descriptor.
This function should be used instead ofos.close()
for better
compatibility across platforms.
(Contributed by Christian Heimes inbpo-32454.)
Thesocket
module now exposes thesocket.TCP_CONGESTION
(Linux 2.6.13),socket.TCP_USER_TIMEOUT
(Linux 2.6.37), and
socket.TCP_NOTSENT_LOWAT
(Linux 3.12) constants.
(Contributed by Omar Sandoval inbpo-26273and
Nathaniel J. Smith inbpo-29728.)
Support forsocket.AF_VSOCK
sockets has been added to allow
communication between virtual machines and their hosts.
(Contributed by Cathy Avery inbpo-27584.)
Sockets now auto-detect family, type and protocol from file descriptor by default. (Contributed by Christian Heimes inbpo-28134.)
socketserver¶
socketserver.ThreadingMixIn.server_close()
now waits until all non-daemon
threads complete.socketserver.ForkingMixIn.server_close()
now waits
until all child processes complete.
Add a newsocketserver.ForkingMixIn.block_on_close
class attribute to
socketserver.ForkingMixIn
andsocketserver.ThreadingMixIn
classes. Set the class attribute toFalse
to get the pre-3.7 behaviour.
sqlite3¶
sqlite3.Connection
now exposes thebackup()
method when the underlying SQLite library is at version 3.6.11 or higher.
(Contributed by Lele Gaifax inbpo-27645.)
Thedatabaseargument ofsqlite3.connect()
now accepts any
path-like object,instead of just a string.
(Contributed by Anders Lorentsen inbpo-31843.)
ssl¶
Thessl
module now uses OpenSSL’s builtin API instead of
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
SSLCertVerificationError
and aborts the handshake with a proper
TLS Alert message. The new exception contains additional information.
Host name validation can be customized with
SSLContext.hostname_checks_common_name
.
(Contributed by Christian Heimes inbpo-31399.)
Note
The improved host name check requires alibsslimplementation compatible with OpenSSL 1.0.2 or 1.1. Consequently, OpenSSL 0.9.8 and 1.0.1 are no longer supported (seePlatform Support Removalsfor more details). The ssl module is mostly compatible with LibreSSL 2.7.2 and newer.
Thessl
module no longer sends IP addresses in SNI TLS extension.
(Contributed by Christian Heimes inbpo-32185.)
match_hostname()
no longer supports partial wildcards like
www*.example.org
.
(Contributed by Mandeep Singh inbpo-23033and Christian Heimes in
bpo-31399.)
The default cipher suite selection of thessl
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 inbpo-31429.)
Validation of server certificates containing internationalized domain names
(IDNs) is now supported. As part of this change, the
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 inbpo-28414.)
Thessl
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,
seeTLS 1.3.
(Contributed by Christian Heimes inbpo-32947,bpo-20995,
bpo-29136,bpo-30622andbpo-33618)
SSLSocket
andSSLObject
no longer have a public
constructor. Direct instantiation was never a documented and supported
feature. Instances must be created withSSLContext
methods
wrap_socket()
andwrap_bio()
.
(Contributed by Christian Heimes inbpo-32951)
OpenSSL 1.1 APIs for setting the minimum and maximum TLS protocol version are
available asSSLContext.minimum_version
andSSLContext.maximum_version
.
Supported protocols are indicated by several new flags, such as
HAS_TLSv1_1
.
(Contributed by Christian Heimes inbpo-32609.)
Addedssl.SSLContext.post_handshake_auth
to enable and
ssl.SSLSocket.verify_client_post_handshake()
to initiate TLS 1.3
post-handshake authentication.
(Contributed by Christian Heimes ingh-78851.)
string¶
string.Template
now lets you to optionally modify the regular
expression pattern for braced placeholders and non-braced placeholders
separately. (Contributed by Barry Warsaw inbpo-1198569.)
subprocess¶
Thesubprocess.run()
function accepts the newcapture_output
keyword argument. When true, stdout and stderr will be captured.
This is equivalent to passingsubprocess.PIPE
asstdoutand
stderrarguments.
(Contributed by Bo Bayles inbpo-32102.)
Thesubprocess.run
function and thesubprocess.Popen
constructor
now accept thetextkeyword argument as an alias
touniversal_newlines.
(Contributed by Andrew Clegg inbpo-31756.)
On Windows the default forclose_fdswas changed fromFalse
to
True
when redirecting the standard handles. It’s now possible to set
close_fdsto true when redirecting the standard handles. See
subprocess.Popen
.This means thatclose_fdsnow defaults to
True
on all supported platforms.
(Contributed by Segev Finer inbpo-19764.)
The subprocess module is now more graceful when handling
KeyboardInterrupt
duringsubprocess.call()
,
subprocess.run()
,or in aPopen
context manager. It now waits a short amount of time for the child
to exit, before continuing the handling of theKeyboardInterrupt
exception.
(Contributed by Gregory P. Smith inbpo-25942.)
sys¶
The newsys.breakpointhook()
hook function is called by the
built-inbreakpoint()
.
(Contributed by Barry Warsaw inbpo-31353.)
On Android, the newsys.getandroidapilevel()
returns the build-time
Android API version.
(Contributed by Victor Stinner inbpo-28740.)
The newsys.get_coroutine_origin_tracking_depth()
function returns
the current coroutine origin tracking depth, as set by
the newsys.set_coroutine_origin_tracking_depth()
.asyncio
has been converted to use this new API instead of
the deprecatedsys.set_coroutine_wrapper()
.
(Contributed by Nathaniel J. Smith inbpo-32591.)
time¶
PEP 564adds six new functions with nanosecond resolution to the
time
module:
New clock identifiers have been added:
time.CLOCK_BOOTTIME
(Linux): Identical totime.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 newtime.thread_time()
andtime.thread_time_ns()
functions
can be used to get per-thread CPU time measurements.
(Contributed by Antoine Pitrou inbpo-32025.)
The newtime.pthread_getcpuclockid()
function returns the clock ID
of the thread-specific CPU-time clock.
tkinter¶
The newtkinter.ttk.Spinbox
class is now available.
(Contributed by Alan Moore inbpo-32585.)
tracemalloc¶
tracemalloc.Traceback
behaves more like regular tracebacks,
sorting the frames from oldest to most recent.
Traceback.format()
now accepts negativelimit,truncating the result to the
abs(limit)
oldest frames. To get the old behaviour, use
the newmost_recent_firstargument toTraceback.format()
.
(Contributed by Jesse Bakker inbpo-32121.)
types¶
The newWrapperDescriptorType
,
MethodWrapperType
,MethodDescriptorType
,
andClassMethodDescriptorType
classes are now available.
(Contributed by Manuel Krebber and Guido van Rossum inbpo-29377,
and Serhiy Storchaka inbpo-32265.)
The newtypes.resolve_bases()
function resolves MRO entries
dynamically as specified byPEP 560.
(Contributed by Ivan Levkivskyi inbpo-32717.)
unicodedata¶
The internalunicodedata
database has been upgraded to useUnicode 11.(Contributed by Benjamin
Peterson.)
unittest¶
The new-k
command-line option allows filtering tests by a name
substring or a Unix shell-like pattern.
For example,Python-munittest-kfoo
runs
foo_tests.SomeTest.test_something
,bar_tests.SomeTest.test_foo
,
but notbar_tests.FooTest.test_something
.
(Contributed by Jonas Haag inbpo-32071.)
unittest.mock¶
Thesentinel
attributes now preserve their identity
when they arecopied
orpickled
.(Contributed by
Serhiy Storchaka inbpo-20804.)
The newseal()
function allows sealing
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 inbpo-30541.)
urllib.parse¶
urllib.parse.quote()
has been updated fromRFC 2396toRFC 3986,
adding~
to the set of characters that are never quoted by default.
(Contributed by Christian Theune and Ratnadeep Debnath inbpo-16285.)
uu¶
Theuu.encode()
function now accepts an optionalbacktick
keyword argument. When it’s true, zeros are represented by'`'
instead of spaces. (Contributed by Xiang Zhang inbpo-30103.)
uuid¶
The newUUID.is_safe
attribute relays information
from the platform about whether generated UUIDs are generated with a
multiprocessing-safe method.
(Contributed by Barry Warsaw inbpo-22807.)
uuid.getnode()
now prefers universally administered
MAC addresses over locally administered MAC addresses.
This makes a better guarantee for global uniqueness of UUIDs returned
fromuuid.uuid1()
.If only locally administered MAC addresses are
available, the first such one found is returned.
(Contributed by Barry Warsaw inbpo-32107.)
warnings¶
The initialization of the default warnings filters has changed as follows:
warnings enabled via command line options (including those for
-b
and the new CPython-specific-X
dev
option) are always passed to the warnings machinery via thesys.warnoptions
attribute.warnings filters enabled via the command line or the environment now have the following order of precedence:
the
BytesWarning
filter for-b
(or-bb
)any filters specified with the
-W
optionany filters specified with the
PYTHONWARNINGS
environment variableany other CPython specific filters (e.g. the
default
filter added for the new-Xdev
mode)any implicit filters defined directly by the warnings machinery
inCPython debug builds,all warnings are now displayed by default (the implicit filter list is empty)
(Contributed by Nick Coghlan and Victor Stinner inbpo-20361, bpo-32043,andbpo-32230.)
Deprecation warnings are once again shown by default in single-file scripts and at the interactive prompt. SeePEP 565: Show DeprecationWarning in __main__for details. (Contributed by Nick Coghlan inbpo-31975.)
xml¶
As mitigation against DTD and external entity retrieval, the
xml.dom.minidom
andxml.sax
modules no longer process
external entities by default.
(Contributed by Christian Heimes ingh-61441.)
xml.etree¶
ElementPathpredicates in thefind()
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 inbpo-31648.)
xmlrpc.server¶
SimpleXMLRPCDispatcher.register_function
can now be used as a decorator. (Contributed by Xiang Zhang in
bpo-7769.)
zipapp¶
Functioncreate_archive()
now accepts an optionalfilter
argument to allow the user to select which files should be included in the
archive. (Contributed by Irmen de Jong inbpo-31072.)
Functioncreate_archive()
now accepts an optionalcompressed
argument to generate a compressed archive. A command line option
--compress
has also been added to support compression.
(Contributed by Zhiming Wang inbpo-31638.)
zipfile¶
ZipFile
now accepts the newcompresslevelparameter to
control the compression level.
(Contributed by Bo Bayles inbpo-21417.)
Subdirectories in archives created byZipFile
are now stored in
Alpha betical order.
(Contributed by Bernhard M. Wiedemann inbpo-30693.)
C API Changes¶
A new API for thread-local storage has been implemented. See PEP 539: New C API for Thread-Local Storagefor an overview and Thread Specific Storage (TSS) APIfor a complete reference. (Contributed by Masayuki Yamamoto inbpo-25658.)
The newcontext variablesfunctionality exposes a number ofnew C APIs.
The newPyImport_GetModule()
function returns the previously
imported module with the given name.
(Contributed by Eric Snow inbpo-28411.)
The newPy_RETURN_RICHCOMPARE
macro eases writing rich
comparison functions.
(Contributed by Petr Victorin inbpo-23699.)
The newPy_UNREACHABLE
macro can be used to mark unreachable
code paths.
(Contributed by Barry Warsaw inbpo-31338.)
Thetracemalloc
now exposes a C API through the new
PyTraceMalloc_Track()
andPyTraceMalloc_Untrack()
functions.
(Contributed by Victor Stinner inbpo-30054.)
The newimport__find__load__start()
and
import__find__load__done()
static markers can be used to trace
module imports.
(Contributed by Christian Heimes inbpo-31574.)
The fieldsname
anddoc
of structures
PyMemberDef
,PyGetSetDef
,
PyStructSequence_Field
,PyStructSequence_Desc
,
andwrapperbase
are now of typeconstchar*
rather of
char*
.(Contributed by Serhiy Storchaka inbpo-28761.)
The result ofPyUnicode_AsUTF8AndSize()
andPyUnicode_AsUTF8()
is now of typeconstchar*
rather ofchar*
.(Contributed by Serhiy
Storchaka inbpo-28769.)
The result ofPyMapping_Keys()
,PyMapping_Values()
and
PyMapping_Items()
is now always a list, rather than a list or a
tuple. (Contributed by Oren Milman inbpo-28280.)
Added functionsPySlice_Unpack()
andPySlice_AdjustIndices()
.
(Contributed by Serhiy Storchaka inbpo-27867.)
PyOS_AfterFork()
is deprecated in favour of the new functions
PyOS_BeforeFork()
,PyOS_AfterFork_Parent()
and
PyOS_AfterFork_Child()
.(Contributed by Antoine Pitrou in
bpo-16500.)
ThePyExc_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
bpo-22898andbpo-30697.
Added C API support for timezones with timezone constructors
PyTimeZone_FromOffset()
andPyTimeZone_FromOffsetAndName()
,
and access to the UTC singleton withPyDateTime_TimeZone_UTC
.
Contributed by Paul Ganssle inbpo-10381.
The type of results ofPyThread_start_new_thread()
and
PyThread_get_thread_ident()
,and theidparameter of
PyThreadState_SetAsyncExc()
changed fromlongto
unsignedlong.
(Contributed by Serhiy Storchaka inbpo-6532.)
PyUnicode_AsWideCharString()
now raises aValueError
if the
second argument isNULL
and thewchar_t*string contains null
characters. (Contributed by Serhiy Storchaka inbpo-30708.)
Changes to the startup sequence and the management of dynamic memory
allocators mean that the long documented requirement to call
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 thePorting to Python 3.7section in this
document and theBefore Python Initializationsection in the C API documentation
for more details.
The newPyInterpreterState_GetID()
returns the unique ID for a
given interpreter.
(Contributed by Eric Snow inbpo-29102.)
Py_DecodeLocale()
,Py_EncodeLocale()
now use the UTF-8
encoding when theUTF-8 modeis enabled.
(Contributed by Victor Stinner inbpo-29240.)
PyUnicode_DecodeLocaleAndSize()
andPyUnicode_EncodeLocale()
now use the current locale encoding forsurrogateescape
error handler.
(Contributed by Victor Stinner inbpo-29240.)
Thestartandendparameters ofPyUnicode_FindChar()
are
now adjusted to behave like string slices.
(Contributed by Xiang Zhang inbpo-28822.)
Build Changes¶
Support for building--without-threads
has been removed. The
threading
module is now always available.
(Contributed by Antoine Pitrou inbpo-31370.).
A full copy of libffi is no longer bundled for use when building the
_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 inbpo-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 (viapy-3.6
), NuGet is used to
download a copy of 32-bit Python for this purpose. (Contributed by Zachary
Ware inbpo-30450.)
Thessl
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.
Optimizations¶
The overhead of calling many methods of various standard library classes
implemented in C has been significantly reduced by porting more code
to use theMETH_FASTCALL
convention.
(Contributed by Victor Stinner inbpo-29300,bpo-29507,
bpo-29452,andbpo-29286.)
Various optimizations have reduced Python startup time by 10% on Linux and up to 30% on macOS. (Contributed by Victor Stinner, INADA Naoki inbpo-29585,and Ivan Levkivskyi inbpo-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 inbpo-26110.)
Theasyncio
module received a number of notable optimizations for
commonly used functions:
The
asyncio.get_event_loop()
function has been reimplemented in C to make it up to 15 times faster. (Contributed by Yury Selivanov inbpo-32296.)asyncio.Future
callback management has been optimized. (Contributed by Yury Selivanov inbpo-32348.)asyncio.gather()
is now up to 15% faster. (Contributed by Yury Selivanov inbpo-32355.)asyncio.sleep()
is now up to 2 times faster when thedelay argument is zero or negative. (Contributed by Andrew Svetlov inbpo-32351.)The performance overhead of asyncio debug mode has been reduced. (Contributed by Antoine Pitrou inbpo-31970.)
As a result ofPEP 560 work,the import time
oftyping
has been reduced by a factor of 7, and many typing operations
are now faster.
(Contributed by Ivan Levkivskyi inbpo-32226.)
sorted()
andlist.sort()
have been optimized for common cases
to be up to 40-75% faster.
(Contributed by Elliot Gorokhovsky inbpo-28685.)
dict.copy()
is now up to 5.5 times faster.
(Contributed by Yury Selivanov inbpo-31179.)
hasattr()
andgetattr()
are now about 4 times faster when
nameis not found andobjdoes not overrideobject.__getattr__()
orobject.__getattribute__()
.
(Contributed by INADA Naoki inbpo-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 inbpo-24821.)
Thecollections.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 inbpo-28638.)
date.fromordinal()
anddate.fromtimestamp()
are now up to
30% faster in the common case.
(Contributed by Paul Ganssle inbpo-32403.)
Theos.fwalk()
function is now up to 2 times faster thanks to
the use ofos.scandir()
.
(Contributed by Serhiy Storchaka inbpo-25996.)
The speed of theshutil.rmtree()
function has been improved by
20–40% thanks to the use of theos.scandir()
function.
(Contributed by Serhiy Storchaka inbpo-28564.)
Optimized case-insensitive matching and searching ofregular
expressions
.Searching some patterns can now be up to 20 times faster.
(Contributed by Serhiy Storchaka inbpo-30285.)
re pile()
now convertsflags
parameter to int object if
it isRegexFlag
.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 inbpo-31671.)
Themodify()
methods of classes
selectors.EpollSelector
,selectors.PollSelector
andselectors.DevpollSelector
may be around 10% faster under
heavy loads. (Contributed by Giampaolo Rodola’ inbpo-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 inbpo-29469and bpo-11549.)
Most functions and methods inabc
have been rewritten in C.
This makes creation of abstract base classes, and callingisinstance()
andissubclass()
on them 1.5x faster. This also reduces Python
start-up time by up to 10%. (Contributed by Ivan Levkivskyi and INADA Naoki
inbpo-31333)
Significant speed improvements to alternate constructors for
datetime.date
anddatetime.datetime
by using fast-path
constructors when not constructing subclasses. (Contributed by Paul Ganssle
inbpo-32403)
The speed of comparison ofarray.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 inbpo-24700.)
Themath.erf()
andmath.erfc()
functions now use the (faster)
C library implementation on most platforms.
(Contributed by Serhiy Storchaka inbpo-26121.)
Other CPython Implementation Changes¶
Trace hooks may now opt out of receiving the
line
and opt into receiving theopcode
events from the interpreter by setting the corresponding newf_trace_lines
andf_trace_opcodes
attributes on the frame being traced. (Contributed by Nick Coghlan inbpo-31344.)Fixed some consistency problems with namespace package module attributes. Namespace module objects now have an
__file__
that is set toNone
(previously unset), and their__spec__.origin
is also set toNone
(previously the string"namespace"
). Seebpo-32305.Also, the namespace module object’s__spec__.loader
is set to the same value as__loader__
(previously, the former was set toNone
). See bpo-32303.The
locals()
dictionary now displays in the lexical order that variables were defined. Previously, the order was undefined. (Contributed by Raymond Hettinger inbpo-32690.)The
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 inbpo-32304.)
Deprecated Python Behavior¶
Yield expressions (bothyield
andyieldfrom
clauses) are now deprecated
in comprehensions and generator expressions (aside from the iterable expression
in the leftmostfor
clause). This ensures that comprehensions
always immediately return a container of the appropriate type (rather than
potentially returning agenerator iteratorobject), 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
DeprecationWarning
when compiled, in Python 3.8 this will be a
SyntaxError
.
(Contributed by Serhiy Storchaka inbpo-10544.)
Returning a subclass ofcomplex
fromobject.__complex__()
is
deprecated and will be an error in future Python versions. This makes
__complex__()
consistent withobject.__int__()
and
object.__float__()
.
(Contributed by Serhiy Storchaka inbpo-28894.)
Deprecated Python modules, functions and methods¶
aifc¶
aifc.openfp()
has been deprecated and will be removed in Python 3.9.
Useaifc.open()
instead.
(Contributed by Brian Curtin inbpo-31985.)
asyncio¶
Support for directlyawait
-ing instances ofasyncio.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 inbpo-32253.)
Theasyncio.Task.current_task()
andasyncio.Task.all_tasks()
methods have been deprecated.
(Contributed by Andrew Svetlov inbpo-32250.)
collections¶
In Python 3.8, the abstract base classes incollections.abc
will no
longer be exposed in the regularcollections
module. This will help
create a clearer distinction between the concrete classes and the abstract
base classes.
(Contributed by Serhiy Storchaka inbpo-25988.)
dbm¶
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 inbpo-28847.)
enum¶
In Python 3.8, attempting to check for non-Enum objects inEnum
classes will raise aTypeError
(e.g.1inColor
); similarly,
attempting to check for non-Flag objects in aFlag
member will
raiseTypeError
(e.g.1inPerm.RW
); currently, both operations
returnFalse
instead.
(Contributed by Ethan Furman inbpo-33217.)
gettext¶
Using non-integer value for selecting a plural form ingettext
is
now deprecated. It never correctly worked. (Contributed by Serhiy Storchaka
inbpo-28692.)
importlib¶
Methods
MetaPathFinder.find_module()
(replaced by
MetaPathFinder.find_spec()
)
and
PathEntryFinder.find_loader()
(replaced by
PathEntryFinder.find_spec()
)
both deprecated in Python 3.4 now emitDeprecationWarning
.
(Contributed by Matthias Bussonnier inbpo-29576.)
Theimportlib.abc.ResourceLoader
ABC has been deprecated in
favour ofimportlib.abc.ResourceReader
.
locale¶
locale.format()
has been deprecated, uselocale.format_string()
instead. (Contributed by Garvit inbpo-10379.)
macpath¶
Themacpath
is now deprecated and will be removed in Python 3.8.
(Contributed by Chi Hsuan Yen inbpo-9850.)
threading¶
dummy_threading
and_dummy_thread
have been deprecated. It is
no longer possible to build Python with threading disabled.
Usethreading
instead.
(Contributed by Antoine Pitrou inbpo-31370.)
socket¶
The silent argument value truncation insocket.htons()
and
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 inbpo-28332.)
ssl¶
ssl.wrap_socket()
is deprecated. Use
ssl.SSLContext.wrap_socket()
instead.
(Contributed by Christian Heimes inbpo-28124.)
sunau¶
sunau.openfp()
has been deprecated and will be removed in Python 3.9.
Usesunau.open()
instead.
(Contributed by Brian Curtin inbpo-31985.)
sys¶
Deprecatedsys.set_coroutine_wrapper()
and
sys.get_coroutine_wrapper()
.
The undocumentedsys.callstats()
function has been deprecated and
will be removed in a future Python version.
(Contributed by Victor Stinner inbpo-28799.)
wave¶
wave.openfp()
has been deprecated and will be removed in Python 3.9.
Usewave.open()
instead.
(Contributed by Brian Curtin inbpo-31985.)
Deprecated functions and types of the C API¶
FunctionPySlice_GetIndicesEx()
is deprecated and replaced with
a macro ifPy_LIMITED_API
is not set or set to a value in the range
between0x03050400
and0x03060000
(not inclusive), or is0x03060100
or higher. (Contributed by Serhiy Storchaka inbpo-27867.)
PyOS_AfterFork()
has been deprecated. UsePyOS_BeforeFork()
,
PyOS_AfterFork_Parent()
orPyOS_AfterFork_Child()
instead.
(Contributed by Antoine Pitrou inbpo-16500.)
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) orUTF-8
(LC_CTYPE
-only locale) as an alternative to the legacyASCII
-basedC
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 ownCI configuration fileprovides an example of using the SSL compatibility testing infrastructurein CPython’s test suite to build and link against OpenSSL 1.1.0 rather than an outdated system provided OpenSSL.
API and Feature Removals¶
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 forre.sub()
were deprecated in Python 3.5, and will now cause an error.Removed support of theexcludeargument in
tarfile.TarFile.add()
. It was deprecated in Python 2.7 and 3.2. Use thefilterargument instead.The
ntpath.splitunc()
function was deprecated in Python 3.1, and has now been removed. Usesplitdrive()
instead.collections.namedtuple()
no longer supports theverboseparameter 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 inbpo-28638.)Functions
bool()
,float()
,list()
andtuple()
no longer take keyword arguments. The first argument ofint()
can now be passed only as positional argument.Removed previously deprecated in Python 2.4 classes
Plist
,Dict
and_InternalDict
in theplistlib
module. Dict values in the result of functionsreadPlist()
andreadPlistFromBytes()
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 thesocket.socketpair()
function instead, it is available on all platforms since Python 3.5.asyncio.windows_utils.socketpair
was just an alias tosocket.socketpair
on Python 3.5 and newer.asyncio
no longer exports theselectors
and_overlapped
modules asasyncio.selectors
andasyncio._overlapped
.Replacefromasyncioimportselectors
withimportselectors
.Direct instantiation of
ssl.SSLSocket
andssl.SSLObject
objects is now prohibited. The constructors were never documented, tested, or designed as public constructors. Users were supposed to usessl.wrap_socket()
orssl.SSLContext
. (Contributed by Christian Heimes inbpo-32951.)The unused
distutils
install_misc
command has been removed. (Contributed by Eric N. Vander Weele inbpo-29218.)
Module Removals¶
Thefpectl
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 inbpo-29137.)
Windows-only Changes¶
The Python launcher, (py.exe), can accept 32 & 64 bit specifierswithout
having to specify a minor version as well. Sopy-3-32
andpy-3-64
become valid as well aspy-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 inbpo-30291.)
The launcher can be run aspy-0
to produce a list of the installed Python s,
with default marked with an asterisk.Runningpy-0p
will include the paths.
If py is run with a version specifier that cannot be matched it will also print
theshort formlist of available specifiers.
(Contributed by Steve Barnes inbpo-30362.)
Porting to Python 3.7¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Changes in Python Behavior¶
async
andawait
names are now reserved keywords. Code using these names as identifiers will now raise aSyntaxError
. (Contributed by Jelle Zijlstra inbpo-30406.)PEP 479is enabled for all code in Python 3.7, meaning that
StopIteration
exceptions raised directly or indirectly in coroutines and generators are transformed intoRuntimeError
exceptions. (Contributed by Yury Selivanov inbpo-32670.)object.__aiter__()
methods can no longer be declared as asynchronous. (Contributed by Yury Selivanov inbpo-31709.)Due to an oversight, earlier Python versions erroneously accepted the following syntax:
f(1forxin[1],) classC(1forxin[1]): pass
Python 3.7 now correctly raises a
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 inbpo-32012andbpo-32023.)When using the
-m
switch, the initial working directory is now added tosys.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 foros.getcwd()
oros.path.dirname(__main__.__file__)
,depending on why the code was checking for the empty string in the first place).
Changes in the Python API¶
socketserver.ThreadingMixIn.server_close()
now waits until all non-daemon threads complete. Set the newsocketserver.ThreadingMixIn.block_on_close
class attribute toFalse
to get the pre-3.7 behaviour. (Contributed by Victor Stinner inbpo-31233andbpo-33540.)socketserver.ForkingMixIn.server_close()
now waits until all child processes complete. Set the newsocketserver.ForkingMixIn.block_on_close
class attribute toFalse
to get the pre-3.7 behaviour. (Contributed by Victor Stinner inbpo-31151andbpo-33540.)The
locale.localeconv()
function now temporarily sets theLC_CTYPE
locale to the value ofLC_NUMERIC
in some cases. (Contributed by Victor Stinner inbpo-31900.)pkgutil.walk_packages()
now raises aValueError
ifpathis a string. Previously an empty list was returned. (Contributed by Sanyam Khurana inbpo-24744.)A format string argument for
string.Formatter.format()
is nowpositional-only. Passing it as a keyword argument was deprecated in Python 3.5. (Contributed by Serhiy Storchaka inbpo-29193.)Attributes
key
,value
andcoded_value
of classhttp.cookies.Morsel
are now read-only. Assigning to them was deprecated in Python 3.5. Use theset()
method for setting them. (Contributed by Serhiy Storchaka inbpo-29192.)Themodeargument of
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 invokingmakedirs()
. (Contributed by Serhiy Storchaka inbpo-19930.)The
struct.Struct.format
type is nowstr
instead ofbytes
.(Contributed by Victor Stinner inbpo-21071.)cgi.parse_multipart()
now accepts theencodinganderrors arguments and returns the same results asFieldStorage
:for non-file fields, the value associated to a key is a list of strings, not bytes. (Contributed by Pierre Quentel inbpo-29979.)Due to internal changes in
socket
,callingsocket.fromshare()
on a socket created bysocket.share
in older Python versions is not supported.repr
forBaseException
has changed to not include the trailing comma. Most exceptions are affected by this change. (Contributed by Serhiy Storchaka inbpo-30399.)repr
fordatetime.timedelta
has changed to include the keyword arguments in the output. (Contributed by Utkarsh Upadhyay inbpo-30302.)Because
shutil.rmtree()
is now implemented using theos.scandir()
function, the user specified handleronerroris now called with the first argumentos.scandir
instead ofos.listdir
when listing the directory is failed.Support for nested sets and set operations in regular expressions as in Unicode Technical Standard #18might be added in the future. This would change the syntax. To facilitate this future change a
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 inbpo-30349.)The result of splitting a string on a
regularexpression
that could match an empty string has been changed. For example splitting onr'\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 tor'\s+'
.AFutureWarning
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 patternr'(?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 asr'(?m)^[^\S\n]*$'
.re.sub()
now replaces empty matches adjacent to a previous non-empty match. For examplere.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’).Change
re.escape()
to only escape regex special characters instead of escaping all characters other than ASCII letters, numbers, and'_'
. (Contributed by Serhiy Storchaka inbpo-29995.)tracemalloc.Traceback
frames are now sorted from oldest to most recent to be more consistent withtraceback
. (Contributed by Jesse Bakker inbpo-32121.)On OSes that support
socket.SOCK_NONBLOCK
orsocket.SOCK_CLOEXEC
bit flags, thesocket.type
no longer has them applied. Therefore, checks likeifsock.type==socket.SOCK_STREAM
work as expected on all platforms. (Contributed by Yury Selivanov inbpo-32331.)On Windows the default for theclose_fdsargument of
subprocess.Popen
was changed fromFalse
toTrue
when redirecting the standard handles. If you previously depended on handles being inherited when usingsubprocess.Popen
with standard io redirection, you will have to passclose_fds=False
to preserve the previous behaviour, or useSTARTUPINFO.lpAttributeList
.importlib.machinery.PathFinder.invalidate_caches()
– which implicitly affectsimportlib.invalidate_caches()
– now deletes entries insys.path_importer_cache
which are set toNone
. (Contributed by Brett Cannon inbpo-33169.)In
asyncio
,loop.sock_recv()
,loop.sock_sendall()
,loop.sock_accept()
,loop.getaddrinfo()
,loop.getnameinfo()
have been changed to be proper coroutine methods to match their documentation. Previously, these methods returnedasyncio.Future
instances. (Contributed by Yury Selivanov inbpo-32327.)asyncio.Server.sockets
now returns a copy of the internal list of server sockets, instead of returning it directly. (Contributed by Yury Selivanov inbpo-32662.)Struct.format
is now astr
instance instead of abytes
instance. (Contributed by Victor Stinner inbpo-21071.)argparse
subparsers can now be made mandatory by passingrequired=True
toArgumentParser.add_subparsers()
. (Contributed by Anthony Sottile inbpo-26510.)ast.literal_eval()
is now stricter. Addition and subtraction of arbitrary numbers are no longer allowed. (Contributed by Serhiy Storchaka inbpo-31778.)Calendar.itermonthdates
will now consistently raise an exception when a date falls outside of the0001-01-01
through9999-12-31
range. To support applications that cannot tolerate such exceptions, the newCalendar.itermonthdays3
andCalendar.itermonthdays4
can be used. The new methods return tuples and are not restricted by the range supported bydatetime.date
. (Contributed by Alexander Belopolsky inbpo-28292.)collections.ChainMap
now preserves the order of the underlying mappings. (Contributed by Raymond Hettinger inbpo-32792.)The
submit()
method ofconcurrent.futures.ThreadPoolExecutor
andconcurrent.futures.ProcessPoolExecutor
now raises aRuntimeError
if called during interpreter shutdown. (Contributed by Mark Nemec inbpo-33097.)The
configparser.ConfigParser
constructor now usesread_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 inbpo-23835.)Several undocumented internal imports were removed. One example is that
os.errno
is no longer available; useimporterrno
directly instead. Note that such undocumented internal imports may be removed any time without notice, even in micro version releases.
Changes in the C API¶
The functionPySlice_GetIndicesEx()
is considered unsafe for
resizable sequences. If the slice indices are not instances ofint
,
but objects that implement the__index__()
method, the sequence can be
resized after passing its length toPySlice_GetIndicesEx()
.This
can lead to returning indices out of the length of the sequence. For
avoiding possible problems use new functionsPySlice_Unpack()
and
PySlice_AdjustIndices()
.
(Contributed by Serhiy Storchaka inbpo-27867.)
CPython bytecode changes¶
There are two new opcodes:LOAD_METHOD
andCALL_METHOD
.
(Contributed by Yury Selivanov and INADA Naoki inbpo-26110.)
TheSTORE_ANNOTATION
opcode has been removed.
(Contributed by Mark Shannon inbpo-32550.)
Windows-only Changes¶
The file used to overridesys.path
is now called
< Python -executable>._pth
instead of'sys.path'
.
SeeFinding modulesfor more information.
(Contributed by Steve Dower inbpo-28137.)
Other CPython implementation changes¶
In preparation for potential future changes to the public CPython runtime initialization API (seePEP 432for 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 bpo-22257,and further updated by Nick, Eric, and Victor Stinner in a number of other issues). Some known details affected:
PySys_AddWarnOptionUnicode()
is not currently usable by embedding applications due to the requirement to create a Unicode object prior to callingPy_Initialize
.UsePySys_AddWarnOption()
instead.warnings filters added by an embedding application with
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,
settingPy_BytesWarningFlag
to a value greater than one is no longer
sufficient to both emitBytesWarning
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 expliciterror::BytesWarning
warnings filter added to convert them to exceptions.
Due to a change in the way docstrings are handled by the compiler, the
implicitreturnNone
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 inbpo-25612.)
Notable changes in Python 3.7.1¶
Starting in 3.7.1,Py_Initialize()
now consistently reads and respects
all of the same environment settings asPy_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 tobpo-34247). If
this behavior is unwanted, setPy_IgnoreEnvironmentFlag
to 1 before
callingPy_Initialize()
.
In 3.7.1 the C API for Context Variables
was updatedto use
PyObject
pointers. See alsobpo-34762.
In 3.7.1 thetokenize
module now implicitly emits aNEWLINE
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 inbpo-33899.)
Notable changes in Python 3.7.2¶
In 3.7.2,venv
on Windows no longer copies the original binaries, but
creates redirector scripts namedPython.exe
andPython w.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.
Notable changes in Python 3.7.6¶
Due to significant security concerns, thereuse_addressparameter of
asyncio.loop.create_datagram_endpoint()
is no longer supported. This is
because of the behavior of the socket optionSO_REUSEADDR
in UDP. For more
details, see the documentation forloop.create_datagram_endpoint()
.
(Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in
bpo-37228.)
Notable changes in Python 3.7.10¶
Earlier Python versions allowed using both;
and&
as
query parameter separators inurllib.parse.parse_qs()
and
urllib.parse.parse_qsl()
.Due to security concerns, and to conform with
newer W3C recommendations, this has been changed to allow only a single
separator key, with&
as the default. This change also affects
cgi.parse()
andcgi.parse_multipart()
as they use the affected
functions internally. For more details, please see their respective
documentation.
(Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin inbpo-42967.)
Notable changes in Python 3.7.11¶
A security fix alters theftplib.FTP
behavior to not trust the
IPv4 address sent from the remote server when setting up a passive data
channel. We reuse the ftp server IP address instead. For unusual code
requiring the old behavior, set atrust_server_pasv_ipv4_address
attribute on your FTP instance toTrue
.(Seegh-87451)
The presence of newline or tab characters in parts of a URL allows for some
forms of attacks. Following the WHATWG specification that updates RFC 3986,
ASCII newline\n
,\r
and tab\t
characters are stripped from the
URL by the parserurllib.parse()
preventing such attacks. The removal
characters are controlled by a new module level variable
urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE
.(Seegh-88048)
Notable security feature in 3.7.14¶
Converting betweenint
andstr
in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal)
now raises aValueError
if the number of digits in string form is
above a limit to avoid potential denial of service attacks due to the
algorithmic complexity. This is a mitigation forCVE 2020-10735.
This limit can be configured or disabled by environment variable, command
line flag, orsys
APIs. See theinteger string conversion
length limitationdocumentation. The default limit
is 4300 digits in string form.