What’s New In Python 3.7¶
Release: | 3.7.0a2 |
---|---|
Date: | November 15, 2017 |
This article explains the new features in Python 3.7, compared to 3.6.
For full details, see the changelog.
Note
Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.7 moves towards release, so it’s worth checking back even after reading earlier versions.
Summary – Release highlights¶
New Features¶
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 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 PYTHONCOERCECLOCALE
environment variable. Automatically setting LC_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 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 stdin
and 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 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
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.
See also
- PEP 538 – Coercing the legacy C locale to a UTF-8 based locale
- PEP written and implemented by Nick Coghlan.
PEP 553: Built-in breakpoint()¶
PEP 553 describes a new built-in called breakpoint()
which makes it
easy and consistent to enter the Python debugger. Built-in breakpoint()
calls sys.breakpointhook()
. By default, this latter imports pdb
and
then calls pdb.set_trace()
, but by binding sys.breakpointhook()
to the
function of your choosing, breakpoint()
can enter any debugger. Or, the
environment variable PYTHONBREAKPOINT
can be set to the callable of
your debugger of choice. Set PYTHONBREAKPOINT=0
to completely disable
built-in breakpoint()
.
See also
- PEP 553 – Built-in breakpoint()
- PEP written and implemented by Barry Warsaw
PEP 539: A New C-API for Thread-Local Storage in CPython¶
While Python provides a C API for thread-local storage support; the existing
Thread Local Storage (TLS) API has used
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 Thread Specific Storage (TSS)
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 Py_tss_t
instead of 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 int
.
Note that on platforms where the native TLS key is defined in a way that cannot
be safely cast to 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.
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 564: Add new time functions with nanosecond resolution¶
Add six new “nanosecond” variants of existing functions to the time
module:
time.clock_gettime_ns()
time.clock_settime_ns()
time.monotonic_ns()
time.perf_counter_ns()
time.process_time_ns()
time.time_ns()
While similar to the existing functions without the _ns
suffix, they
provide nanosecond resolution: they return a number of nanoseconds as a Python
int
.
The time.time_ns()
resolution is 3 times better than the time.time()
resolution on Linux and Windows.
See also
- PEP 564 – Add new time functions with nanosecond resolution
- PEP written and implemented by Victor Stinner
Other Language Changes¶
- 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-12844 and bpo-18896.)
bytes.fromhex()
andbytearray.fromhex()
now ignore all ASCII whitespace, not only spaces. (Contributed by Robert Xiao in bpo-28927.)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 in bpo-30024.)
object.__format__(x, '')
is now equivalent tostr(x)
rather thanformat(str(self), '')
. (Contributed by Serhiy Storchaka in bpo-28974.)
New Modules¶
- None yet.
Improved Modules¶
argparse¶
The parse_intermixed_args()
supports letting
the user intermix options and positional arguments on the command line,
as is possible in many unix commands. It supports most but not all
argparse features. (Contributed by paul.j3 in bpo-14191.)
binascii¶
The 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 bpo-30103.)
calendar¶
The class HTMLCalendar
has new class attributes which ease
the customisation of the CSS classes in the produced HTML calendar.
(Contributed by Oz Tiram in bpo-30095.)
cgi¶
parse_multipart()
returns the same results as
FieldStorage
: for non-file fields, the value associated to a key
is a list of strings, not bytes.
(Contributed by Pierre Quentel in bpo-29979.)
contextlib¶
contextlib.asynccontextmanager()
has been added. (Contributed by
Jelle Zijlstra in bpo-29679.)
cProfile¶
cProfile command line now accepts -m module_name as an alternative to script path. (Contributed by Sanyam Khurana in bpo-21862.)
dis¶
The dis()
function now is able to
disassemble nested code objects (the code of comprehensions, generator
expressions and nested functions, and the code used for building nested
classes). (Contributed by Serhiy Storchaka in bpo-11822.)
distutils¶
README.rst is now included in the list of distutils standard READMEs and therefore included in source distributions. (Contributed by Ryan Gonzalez in bpo-11913.)
http.client¶
Add Configurable blocksize to HTTPConnection
and
HTTPSConnection
for improved upload throughput.
(Contributed by Nir Soffer in bpo-31945.)
http.server¶
SimpleHTTPRequestHandler
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 bpo-29654.)
Add the parameter directory
to the SimpleHTTPRequestHandler
and the --directory
to the command line of the module server
.
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 bpo-28707.)
locale¶
Added another argument monetary in format_string()
of locale
.
If monetary is true, the conversion uses monetary thousands separator and
grouping strings. (Contributed by Garvit in bpo-10379.)
math¶
New remainder()
function, implementing the IEEE 754-style remainder
operation. (Contributed by Mark Dickinson in bpo-29962.)
os¶
Added support for bytes
paths in fwalk()
. (Contributed by
Serhiy Storchaka in bpo-28682.)
Added support for file descriptors in scandir()
on Unix. (Contributed by Serhiy Storchaka in bpo-25996.)
New function os.register_at_fork()
allows registering Python callbacks
to be executed on a process fork. (Contributed by Antoine Pitrou in
bpo-16500.)
pdb¶
set_trace()
now takes an optional header keyword-only
argument. If given, this is printed to the console just before debugging
begins. (Contributed by Barry Warsaw in bpo-31389.)
re¶
The flags re.ASCII
, re.LOCALE
and re.UNICODE
can be set within the scope of a group.
(Contributed by Serhiy Storchaka in bpo-31690.)
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 in bpo-1198569.)
time¶
The PEP 564 added six new functions with nanosecond resolution:
time.clock_gettime_ns()
time.clock_settime_ns()
time.monotonic_ns()
time.perf_counter_ns()
time.process_time_ns()
time.time_ns()
Add new clock identifiers:
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 timer from the CPU.time.CLOCK_UPTIME
(FreeBSD, OpenBSD): Time whose absolute value is the time the system has been running and not suspended, providing accurate uptime measurement, both absolute and interval.
unittest.mock¶
The sentinel
attributes now preserve their identity
when they are copied
or pickled
. (Contributed by
Serhiy Storchaka in bpo-20804.)
New function seal
will disable the creation of mock
children by preventing to get or set any new attribute on the sealed mock.
The sealing process is performed recursively. (Contributed by Mario Corchero
in bpo-30541.)
xmlrpc.server¶
register_function()
of xmlrpc.server.SimpleXMLRPCDispatcher
and
its subclasses can be used as a decorator. (Contributed by Xiang Zhang in
bpo-7769.)
unicodedata¶
The internal unicodedata
database has been upgraded to use Unicode 10. (Contributed by Benjamin
Peterson.)
urllib.parse¶
urllib.parse.quote()
has been updated from RFC 2396 to RFC 3986,
adding ~ to the set of characters that is never quoted by default.
(Contributed by Christian Theune and Ratnadeep Debnath in bpo-16285.)
uu¶
Function encode()
now accepts an optional backtick
keyword argument. When it’s true, zeros are represented by '`'
instead of spaces. (Contributed by Xiang Zhang in bpo-30103.)
xml.etree¶
ElementPath predicates in the 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 bpo-31648.)
zipapp¶
Function zipapp.create_archive()
now accepts an optional filter
argument to allow the user to select which files should be included in the
archive, and an optional compressed argument to generate a compressed
archive.
A command line option --compress
has also been added to support
compression.
Optimizations¶
- Added two new opcodes:
LOAD_METHOD
andCALL_METHOD
to avoid instantiation of bound method objects for method calls, which results in method calls being faster up to 20%. (Contributed by Yury Selivanov and INADA Naoki in bpo-26110.) - Searching some unlucky Unicode characters (like Ukrainian capital “Є”) in a string was up to 25 times slower than searching other characters. Now it is slower only by 3 times in the worst case. (Contributed by Serhiy Storchaka in bpo-24821.)
- Fast implementation from standard C library is now used for functions
erf()
anderfc()
in themath
module. (Contributed by Serhiy Storchaka in bpo-26121.) - The
os.fwalk()
function has been sped up by 2 times. This was done using theos.scandir()
function. (Contributed by Serhiy Storchaka in bpo-25996.) - The
shutil.rmtree()
function has been sped up to 20–40%. This was done using theos.scandir()
function. (Contributed by Serhiy Storchaka in bpo-28564.) - Optimized case-insensitive matching and searching of
regular expressions
. Searching some patterns can now be up to 20 times faster. (Contributed by Serhiy Storchaka in bpo-30285.) re.compile()
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 in bpo-31671.)selectors.EpollSelector.modify()
,selectors.PollSelector.modify()
andselectors.DevpollSelector.modify()
may be around 10% faster under heavy loads. (Contributed by Giampaolo Rodola’ in bpo-30014)
Build and C API Changes¶
- 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 in bpo-27979. - The fields
name
anddoc
of structuresPyMemberDef
,PyGetSetDef
,PyStructSequence_Field
,PyStructSequence_Desc
, andwrapperbase
are now of typeconst char *
rather ofchar *
. (Contributed by Serhiy Storchaka in bpo-28761.) - The result of
PyUnicode_AsUTF8AndSize()
andPyUnicode_AsUTF8()
is now of typeconst char *
rather ofchar *
. (Contributed by Serhiy Storchaka in bpo-28769.) - The result of
PyMapping_Keys()
,PyMapping_Values()
andPyMapping_Items()
is now always a list, rather than a list or a tuple. (Contributed by Oren Milman in bpo-28280.) - Added functions
PySlice_Unpack()
andPySlice_AdjustIndices()
. (Contributed by Serhiy Storchaka in bpo-27867.) PyOS_AfterFork()
is deprecated in favour of the new functionsPyOS_BeforeFork()
,PyOS_AfterFork_Parent()
andPyOS_AfterFork_Child()
. (Contributed by Antoine Pitrou in bpo-16500.)- 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 bpo-30450.) - 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 bpo-22898 and bpo-30697. - Support for building
--without-threads
is removed. (Contributed by Antoine Pitrou in bpo-31370.).
Other CPython Implementation Changes¶
- Trace hooks may now opt out of receiving
line
events from the interpreter by setting the newf_trace_lines
attribute toFalse
on the frame being traced. (Contributed by Nick Coghlan in bpo-31344.) - Trace hooks may now opt in to receiving
opcode
events from the interpreter by setting the newf_trace_opcodes
attribute toTrue
on the frame being traced. (Contributed by Nick Coghlan in bpo-31344.)
Deprecated¶
- Function
PySlice_GetIndicesEx()
is deprecated and replaced with a macro ifPy_LIMITED_API
is not set or set to the value between0x03050400
and0x03060000
(not including) or0x03060100
or higher. (Contributed by Serhiy Storchaka in bpo-27867.) - Deprecated
format()
fromlocale
, use theformat_string()
instead. (Contributed by Garvit in bpo-10379.) - Methods
MetaPathFinder.find_module()
(replaced byMetaPathFinder.find_spec()
) andPathEntryFinder.find_loader()
(replaced byPathEntryFinder.find_spec()
) both deprecated in Python 3.4 now emitDeprecationWarning
. (Contributed by Matthias Bussonnier in bpo-29576) - Using non-integer value for selecting a plural form in
gettext
is now deprecated. It never correctly worked. (Contributed by Serhiy Storchaka in bpo-28692.) - The
macpath
is now deprecated and will be removed in Python 3.8.
Changes in the C API¶
- The type of results of
PyThread_start_new_thread()
andPyThread_get_thread_ident()
, and the id parameter ofPyThreadState_SetAsyncExc()
changed fromlong
tounsigned long
. (Contributed by Serhiy Storchaka in bpo-6532.) PyUnicode_AsWideCharString()
now raises aValueError
if the second argument is NULL and thewchar_t*
string contains null characters. (Contributed by Serhiy Storchaka in bpo-30708.)
Windows Only¶
- The python launcher, (py.exe), can accept 32 & 64 bit specifiers without
having to specify a minor version as well. So
py -3-32
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 in bpo-30291.) - The launcher can be run as “py -0” to produce a list of the installed pythons, with default marked with an asterix. Running “py -0p” will include the paths. If py is run with a version specifier that cannot be matched it will also print the short form list of available specifiers. (Contributed by Steve Barnes in bpo-30362.)
Removed¶
API and Feature Removals¶
- 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 the exclude argument in
tarfile.TarFile.add()
. It was deprecated in Python 2.7 and 3.2. Use the filter argument instead. - The
splitunc()
function in thentpath
module was deprecated in Python 3.1, and has now been removed. Use thesplitdrive()
function instead. 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 bpo-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.
Porting to Python 3.7¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Changes in the Python API¶
pkgutil.walk_packages()
now raises ValueError if path is a string. Previously an empty list was returned. (Contributed by Sanyam Khurana in bpo-24744.)- A format string argument for
string.Formatter.format()
is now positional-only. Passing it as a keyword argument was deprecated in Python 3.5. (Contributed by Serhiy Storchaka in bpo-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 in bpo-29192.) Module
,FunctionDef
,AsyncFunctionDef
, andClassDef
AST nodes now have a newdocstring
field. The first statement in their body is not considered as a docstring anymore.co_firstlineno
andco_lnotab
of code object for class and module are affected by this change. (Contributed by INADA Naoki and Eugene Toder in bpo-29463.)- The mode argument 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 in bpo-19930.) - The
struct.Struct.format
type is nowstr
instead ofbytes
. (Contributed by Victor Stinner in bpo-21071.) - Due to internal changes in
socket
you won’t be able tosocket.fromshare()
a socketshare()
-ed in older Python versions. repr
fordatetime.timedelta
has changed to include keyword arguments in the output. (Contributed by Utkarsh Upadhyay in bpo-30302.)- Because
shutil.rmtree()
is now implemented using theos.scandir()
function, the user specified handler onerror is now called with the first argumentos.scandir
instead ofos.listdir
when listing the direcory is failed.
Changes in the C API¶
- The function
PySlice_GetIndicesEx()
is considered not safe 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()
andPySlice_AdjustIndices()
. (Contributed by Serhiy Storchaka in bpo-27867.)
CPython bytecode changes¶
- Added two new opcodes:
LOAD_METHOD
andCALL_METHOD
. (Contributed by Yury Selivanov and INADA Naoki in bpo-26110.)
Other CPython implementation changes¶
- In preparation for potential future changes to the public CPython runtime initialization API (see PEP 432 for details), 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. (Contributed by Nick Coghlan and Eric Snow as part of bpo-22257.)
Documentation¶
PEP 545: Python Documentation Translations¶
PEP 545 describes the process to translate Python documentation, and two translations have been added:
- Japanese: https://docs.python.org/ja/ and associated GitHub repository: https://github.com/python/python-docs-ja
- French: https://docs.python.org/fr/ and associated GitHub repository: https://github.com/python/python-docs-fr
(Contributed by Julien Palard, Inada Naoki, and Victor Stinner in bpo-26546.)