What’s New In Python 3.6¶
Release: | 3.6.0b2 |
---|---|
Date: | October 11, 2016 |
This article explains the new features in Python 3.6, compared to 3.5.
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 3.6 moves towards release, so it’s worth checking back even after reading earlier versions.
Summary – Release highlights¶
New syntax features:
- A
global
ornonlocal
statement must now textually appear before the first use of the affected name in the same scope. Previously this was a SyntaxWarning. - PEP 498: Formatted string literals
- PEP 515: Underscores in Numeric Literals
- PEP 526: Syntax for Variable Annotations
- PEP 525: Asynchronous Generators
- PEP 530: Asynchronous Comprehensions
Standard library improvements:
Security improvements:
- On Linux,
os.urandom()
now blocks until the system urandom entropy pool is initialized to increase the security. See the PEP 524 for the rationale. hashlib
andssl
now support OpenSSL 1.1.0.- The default settings and feature set of the
ssl
have been improved. - The
hashlib
module has got support for BLAKE2, SHA-3 and SHAKE hash algorithms andscrypt()
key derivation function.
Windows improvements:
- PEP 529: Change Windows filesystem encoding to UTF-8
- PEP 528: Change Windows console encoding to UTF-8
- The
py.exe
launcher, when used interactively, no longer prefers Python 2 over Python 3 when the user doesn’t specify a version (via command line arguments or a config file). Handling of shebang lines remains unchanged - “python” refers to Python 2 in that case. python.exe
andpythonw.exe
have been marked as long-path aware, which means that when the 260 character path limit may no longer apply. See removing the MAX_PATH limitation for details.- A
._pth
file can be added to force isolated mode and fully specify all search paths to avoid registry and environment lookup. See the documentation for more information. - A
python36.zip
file now works as a landmark to inferPYTHONHOME
. See the documentation for more information.
New built-in features:
- PEP 520: Preserving Class Attribute Definition Order
- PEP 468: Preserving Keyword Argument Order
A complete list of PEP’s implemented in Python 3.6:
- PEP 468, Preserving Keyword Argument Order
- PEP 487, Simpler customization of class creation
- PEP 495, Local Time Disambiguation
- PEP 498, Formatted string literals
- PEP 506, Adding A Secrets Module To The Standard Library
- PEP 509, Add a private version to dict
- PEP 515, Underscores in Numeric Literals
- PEP 519, Adding a file system path protocol
- PEP 520, Preserving Class Attribute Definition Order
- PEP 523, Adding a frame evaluation API to CPython
- PEP 524, Make os.urandom() blocking on Linux (during system startup)
- PEP 525, Asynchronous Generators (provisional)
- PEP 526, Syntax for Variable Annotations (provisional)
- PEP 528, Change Windows console encoding to UTF-8 (provisional)
- PEP 529, Change Windows filesystem encoding to UTF-8 (provisional)
- PEP 530, Asynchronous Comprehensions
New Features¶
PEP 515: Underscores in Numeric Literals¶
Prior to PEP 515, there was no support for writing long numeric
literals with some form of separator to improve readability. For
instance, how big is 1000000000000000
? With PEP 515, though,
you can use underscores to separate digits as desired to make numeric
literals easier to read: 1_000_000_000_000_000
. Underscores can be
used with other numeric literals beyond integers, e.g.
0x_FF_FF_FF_FF
.
Single underscores are allowed between digits and after any base specifier. More than a single underscore in a row, leading, or trailing underscores are not allowed.
See also
- PEP 515 – Underscores in Numeric Literals
- PEP written by Georg Brandl and Serhiy Storchaka.
PEP 523: Adding a frame evaluation API to CPython¶
While Python provides extensive support to customize how code executes, one place it has not done so is in the evaluation of frame objects. If you wanted some way to intercept frame evaluation in Python there really wasn’t any way without directly manipulating function pointers for defined functions.
PEP 523 changes this by providing an API to make frame evaluation pluggable at the C level. This will allow for tools such as debuggers and JITs to intercept frame evaluation before the execution of Python code begins. This enables the use of alternative evaluation implementations for Python code, tracking frame evaluation, etc.
This API is not part of the limited C API and is marked as private to signal that usage of this API is expected to be limited and only applicable to very select, low-level use-cases. Semantics of the API will change with Python as necessary.
See also
- PEP 523 – Adding a frame evaluation API to CPython
- PEP written by Brett Cannon and Dino Viehland.
PEP 519: Adding a file system path protocol¶
File system paths have historically been represented as str
or bytes
objects. This has led to people who write code which
operate on file system paths to assume that such objects are only one
of those two types (an int
representing a file descriptor
does not count as that is not a file path). Unfortunately that
assumption prevents alternative object representations of file system
paths like pathlib
from working with pre-existing code,
including Python’s standard library.
To fix this situation, a new interface represented by
os.PathLike
has been defined. By implementing the
__fspath__()
method, an object signals that it
represents a path. An object can then provide a low-level
representation of a file system path as a str
or
bytes
object. This means an object is considered
path-like if it implements
os.PathLike
or is a str
or bytes
object
which represents a file system path. Code can use os.fspath()
,
os.fsdecode()
, or os.fsencode()
to explicitly get a
str
and/or bytes
representation of a path-like
object.
The built-in open()
function has been updated to accept
os.PathLike
objects as have all relevant functions in the
os
and os.path
modules. PyUnicode_FSConverter()
and PyUnicode_FSConverter()
have been changed to accept
path-like objects. The os.DirEntry
class
and relevant classes in pathlib
have also been updated to
implement os.PathLike
.
The hope in is that updating the fundamental functions for operating
on file system paths will lead to third-party code to implicitly
support all path-like objects without any
code changes or at least very minimal ones (e.g. calling
os.fspath()
at the beginning of code before operating on a
path-like object).
Here are some examples of how the new interface allows for
pathlib.Path
to be used more easily and transparently with
pre-existing code:
>>> import pathlib
>>> with open(pathlib.Path("README")) as f:
... contents = f.read()
...
>>> import os.path
>>> os.path.splitext(pathlib.Path("some_file.txt"))
('some_file', '.txt')
>>> os.path.join("/a/b", pathlib.Path("c"))
'/a/b/c'
>>> import os
>>> os.fspath(pathlib.Path("some_file.txt"))
'some_file.txt'
(Implemented by Brett Cannon, Ethan Furman, Dusty Phillips, and Jelle Zijlstra.)
See also
- PEP 519 – Adding a file system path protocol
- PEP written by Brett Cannon and Koos Zevenhoven.
PEP 498: Formatted string literals¶
Formatted string literals are a new kind of string literal, prefixed
with 'f'
. They are similar to the format strings accepted by
str.format()
. They contain replacement fields surrounded by
curly braces. The replacement fields are expressions, which are
evaluated at run time, and then formatted using the format()
protocol:
>>> name = "Fred"
>>> f"He said his name is {name}."
'He said his name is Fred.'
See PEP 498 and the main documentation at Formatted string literals.
PEP 526: Syntax for variable annotations¶
PEP 484 introduced standard for type annotations of function parameters, a.k.a. type hints. This PEP adds syntax to Python for annotating the types of variables including class variables and instance variables:
primes: List[int] = []
captain: str # Note: no initial value!
class Starship:
stats: Dict[str, int] = {}
Just as for function annotations, the Python interpreter does not attach any
particular meaning to variable annotations and only stores them in a special
attribute __annotations__
of a class or module.
In contrast to variable declarations in statically typed languages,
the goal of annotation syntax is to provide an easy way to specify structured
type metadata for third party tools and libraries via the abstract syntax tree
and the __annotations__
attribute.
PEP 529: Change Windows filesystem encoding to UTF-8¶
Representing filesystem paths is best performed with str (Unicode) rather than bytes. However, there are some situations where using bytes is sufficient and correct.
Prior to Python 3.6, data loss could result when using bytes paths on Windows.
With this change, using bytes to represent paths is now supported on Windows,
provided those bytes are encoded with the encoding returned by
sys.getfilesystemencoding()
, which now defaults to 'utf-8'
.
Applications that do not use str to represent paths should use
os.fsencode()
and os.fsdecode()
to ensure their bytes are
correctly encoded. To revert to the previous behaviour, set
PYTHONLEGACYWINDOWSFSENCODING
or call
sys._enablelegacywindowsfsencoding()
.
See PEP 529 for more information and discussion of code modifications that may be required.
Note
This change is considered experimental for 3.6.0 beta releases. The default encoding may change before the final release.
PEP 487: Simpler customization of class creation¶
Upon subclassing a class, the __init_subclass__
classmethod (if defined) is
called on the base class. This makes it straightforward to write classes that
customize initialization of future subclasses without introducing the
complexity of a full custom metaclass.
The descriptor protocol has also been expanded to include a new optional method,
__set_name__
. Whenever a new class is defined, the new method will be called
on all descriptors included in the definition, providing them with a reference
to the class being defined and the name given to the descriptor within the
class namespace.
Also see PEP 487 and the updated class customization documentation at Customizing class creation and Implementing Descriptors.
(Contributed by Martin Teichmann in issue 27366)
PEP 528: Change Windows console encoding to UTF-8¶
The default console on Windows will now accept all Unicode characters and
provide correctly read str objects to Python code. sys.stdin
,
sys.stdout
and sys.stderr
now default to utf-8 encoding.
This change only applies when using an interactive console, and not when
redirecting files or pipes. To revert to the previous behaviour for interactive
console use, set PYTHONLEGACYWINDOWSIOENCODING
.
See also
- PEP 528 – Change Windows console encoding to UTF-8
- PEP written and implemented by Steve Dower.
PYTHONMALLOC environment variable¶
The new PYTHONMALLOC
environment variable allows setting the Python
memory allocators and/or install debug hooks.
It is now possible to install debug hooks on Python memory allocators on Python
compiled in release mode using PYTHONMALLOC=debug
. Effects of debug hooks:
- Newly allocated memory is filled with the byte
0xCB
- Freed memory is filled with the byte
0xDB
- Detect violations of Python memory allocator API. For example,
PyObject_Free()
called on a memory block allocated byPyMem_Malloc()
. - Detect write before the start of the buffer (buffer underflow)
- Detect write after the end of the buffer (buffer overflow)
- Check that the GIL is held when allocator
functions of
PYMEM_DOMAIN_OBJ
(ex:PyObject_Malloc()
) andPYMEM_DOMAIN_MEM
(ex:PyMem_Malloc()
) domains are called.
Checking if the GIL is held is also a new feature of Python 3.6.
See the PyMem_SetupDebugHooks()
function for debug hooks on Python
memory allocators.
It is now also possible to force the usage of the malloc()
allocator of
the C library for all Python memory allocations using PYTHONMALLOC=malloc
.
It helps to use external memory debuggers like Valgrind on a Python compiled in
release mode.
On error, the debug hooks on Python memory allocators now use the
tracemalloc
module to get the traceback where a memory block was
allocated.
Example of fatal error on buffer overflow using
python3.6 -X tracemalloc=5
(store 5 frames in traces):
Debug memory block at address p=0x7fbcd41666f8: API 'o'
4 bytes originally requested
The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
The 8 pad bytes at tail=0x7fbcd41666fc are not all FORBIDDENBYTE (0xfb):
at tail+0: 0x02 *** OUCH
at tail+1: 0xfb
at tail+2: 0xfb
at tail+3: 0xfb
at tail+4: 0xfb
at tail+5: 0xfb
at tail+6: 0xfb
at tail+7: 0xfb
The block was made by call #1233329 to debug malloc/realloc.
Data at p: 1a 2b 30 00
Memory block allocated at (most recent call first):
File "test/test_bytes.py", line 323
File "unittest/case.py", line 600
File "unittest/case.py", line 648
File "unittest/suite.py", line 122
File "unittest/suite.py", line 84
Fatal Python error: bad trailing pad byte
Current thread 0x00007fbcdbd32700 (most recent call first):
File "test/test_bytes.py", line 323 in test_hex
File "unittest/case.py", line 600 in run
File "unittest/case.py", line 648 in __call__
File "unittest/suite.py", line 122 in run
File "unittest/suite.py", line 84 in __call__
File "unittest/suite.py", line 122 in run
File "unittest/suite.py", line 84 in __call__
...
(Contributed by Victor Stinner in issue 26516 and issue 26564.)
DTrace and SystemTap probing support¶
Python can now be built --with-dtrace
which enables static markers
for the following events in the interpreter:
- function call/return
- garbage collection started/finished
- line of code executed.
This can be used to instrument running interpreters in production, without the need to recompile specific debug builds or providing application-specific profiling/debugging code.
More details in Instrumenting CPython with DTrace and SystemTap.
The current implementation is tested on Linux and macOS. Additional markers may be added in the future.
(Contributed by Łukasz Langa in issue 21590, based on patches by Jesús Cea Avión, David Malcolm, and Nikhil Benesch.)
PEP 520: Preserving Class Attribute Definition Order¶
Attributes in a class definition body have a natural ordering: the same
order in which the names appear in the source. This order is now
preserved in the new class’s __dict__
attribute.
Also, the effective default class execution namespace (returned from
type.__prepare__()
) is now an insertion-order-preserving mapping.
See also
- PEP 520 – Preserving Class Attribute Definition Order
- PEP written and implemented by Eric Snow.
PEP 468: Preserving Keyword Argument Order¶
**kwargs
in a function signature is now guaranteed to be an
insertion-order-preserving mapping.
See also
- PEP 468 – Preserving Keyword Argument Order
- PEP written and implemented by Eric Snow.
PEP 509: Add a private version to dict¶
Add a new private version to the builtin dict
type, incremented at
each dictionary creation and at each dictionary change, to implement
fast guards on namespaces.
(Contributed by Victor Stinner in issue 26058.)
Other Language Changes¶
Some smaller changes made to the core Python language are:
dict()
now uses a “compact” representation pioneered by PyPy. The memory usage of the newdict()
is between 20% and 25% smaller compared to Python 3.5. PEP 468 (Preserving the order of**kwargs
in a function.) is implemented by this. The order-preserving aspect of this new implementation is considered an implementation detail and should not be relied upon (this may change in the future, but it is desired to have this new dict implementation in the language for a few releases before changing the language spec to mandate order-preserving semantics for all current and future Python implementations; this also helps preserve backwards-compatibility with older versions of the language where random iteration order is still in effect, e.g. Python 3.5). (Contributed by INADA Naoki in issue 27350. Idea originally suggested by Raymond Hettinger.)- Long sequences of repeated traceback lines are now abbreviated as
"[Previous line repeated {count} more times]"
(see traceback for an example). (Contributed by Emanuel Barry in issue 26823.) - Import now raises the new exception
ModuleNotFoundError
(subclass ofImportError
) when it cannot find a module. Code that current checks for ImportError (in try-except) will still work.
New Modules¶
- None yet.
Improved Modules¶
On Linux, os.urandom()
now blocks until the system urandom entropy pool
is initialized to increase the security. See the PEP 524 for the rationale.
asyncio¶
Since the asyncio
module is provisional,
all changes introduced in Python 3.6 have also been backported to Python
3.5.x.
Notable changes in the asyncio
module since Python 3.5.0:
- The
ensure_future()
function and all functions that use it, such asloop.run_until_complete()
, now accept all kinds of awaitable objects. (Contributed by Yury Selivanov.) - New
run_coroutine_threadsafe()
function to submit coroutines to event loops from other threads. (Contributed by Vincent Michel.) - New
Transport.is_closing()
method to check if the transport is closing or closed. (Contributed by Yury Selivanov.) - The
loop.create_server()
method can now accept a list of hosts. (Contributed by Yann Sionneau.) - New
loop.create_future()
method to create Future objects. This allows alternative event loop implementations, such as uvloop, to provide a fasterasyncio.Future
implementation. (Contributed by Yury Selivanov.) - New
loop.get_exception_handler()
method to get the current exception handler. (Contributed by Yury Selivanov.) - New
StreamReader.readuntil()
method to read data from the stream until a separator bytes sequence appears. (Contributed by Mark Korenberg.) - The
loop.getaddrinfo()
method is optimized to avoid calling the systemgetaddrinfo
function if the address is already resolved. (Contributed by A. Jesse Jiryu Davis.)
contextlib¶
The contextlib.AbstractContextManager
class has been added to
provide an abstract base class for context managers. It provides a
sensible default implementation for __enter__() which returns
self
and leaves __exit__() an abstract method. A matching
class has been added to the typing
module as
typing.ContextManager
.
(Contributed by Brett Cannon in issue 25609.)
venv¶
venv
accepts a new parameter --prompt
. This parameter provides an
alternative prefix for the virtual environment. (Proposed by Łukasz.Balcerzak
and ported to 3.6 by Stéphane Wirtel in issue 22829.)
datetime¶
The datetime.strftime()
and
date.strftime()
methods now support ISO 8601 date
directives %G
, %u
and %V
.
(Contributed by Ashley Anderson in issue 12006.)
distutils.command.sdist¶
The default_format
attribute has been removed from
distutils.command.sdist.sdist
and the formats
attribute defaults to ['gztar']
. Although not anticipated,
Any code relying on the presence of default_format
may
need to be adapted. See issue 27819 for more details.
email¶
The new email API, enabled via the policy keyword to various constructors, is
no longer provisional. The email
documentation has been reorganized and
rewritten to focus on the new API, while retaining the old documentation for
the legacy API. (Contributed by R. David Murray in issue 24277.)
The email.mime
classes now all accept an optional policy keyword.
(Contributed by Berker Peksag in issue 27331.)
The DecodedGenerator
now supports the policy
keyword.
There is a new policy
attribute,
message_factory
, that controls what class is used
by default when the parser creates new message objects. For the
email.policy.compat32
policy this is Message
,
for the new policies it is EmailMessage
.
(Contributed by R. David Murray in issue 20476.)
encodings¶
On Windows, added the 'oem'
encoding to use CP_OEMCP
and the 'ansi'
alias for the existing 'mbcs'
encoding, which uses the CP_ACP
code page.
faulthandler¶
On Windows, the faulthandler
module now installs a handler for Windows
exceptions: see faulthandler.enable()
. (Contributed by Victor Stinner in
issue 23848.)
hashlib¶
hashlib
supports OpenSSL 1.1.0. The minimum recommend version is 1.0.2.
It has been tested with 0.9.8zc, 0.9.8zh and 1.0.1t as well as LibreSSL 2.3
and 2.4.
(Contributed by Christian Heimes in issue 26470.)
BLAKE2 hash functions were added to the module. blake2b()
and blake2s()
are always available and support the full
feature set of BLAKE2.
(Contributed by Christian Heimes in issue 26798 based on code by
Dmitry Chestnykh and Samuel Neves. Documentation written by Dmitry Chestnykh.)
The SHA-3 hash functions sha3_224()
, sha3_256()
,
sha3_384()
, sha3_512()
, and SHAKE hash functions
shake_128()
and shake_256()
were added.
(Contributed by Christian Heimes in issue 16113. Keccak Code Package
by Guido Bertoni, Joan Daemen, Michaël Peeters, Gilles Van Assche, and
Ronny Van Keer.)
The password-based key derivation function scrypt()
is now
available with OpenSSL 1.1.0 and newer.
(Contributed by Christian Heimes in issue 27928.)
http.client¶
HTTPConnection.request()
and
endheaders()
both now support
chunked encoding request bodies.
(Contributed by Demian Brecht and Rolf Krahl in issue 12319.)
idlelib and IDLE¶
The idlelib package is being modernized and refactored to make IDLE look and work better and to make the code easier to understand, test, and improve. Part of making IDLE look better, especially on Linux and Mac, is using ttk widgets, mostly in the dialogs. As a result, IDLE no longer runs with tcl/tk 8.4. It now requires tcl/tk 8.5 or 8.6. We recommend running the latest release of either.
‘Modernizing’ includes renaming and consolidation of idlelib modules. The renaming of files with partial uppercase names is similar to the renaming of, for instance, Tkinter and TkFont to tkinter and tkinter.font in 3.0. As a result, imports of idlelib files that worked in 3.5 will usually not work in 3.6. At least a module name change will be needed (see idlelib/README.txt), sometimes more. (Name changes contributed by Al Swiegart and Terry Reedy in issue 24225. Most idlelib patches since have been and will be part of the process.)
In compensation, the eventual result with be that some idlelib classes will be easier to use, with better APIs and docstrings explaining them. Additional useful information will be added to idlelib when available.
importlib¶
importlib.util.LazyLoader
now calls
create_module()
on the wrapped loader, removing the
restriction that importlib.machinery.BuiltinImporter
and
importlib.machinery.ExtensionFileLoader
couldn’t be used with
importlib.util.LazyLoader
.
importlib.util.cache_from_source()
,
importlib.util.source_from_cache()
, and
importlib.util.spec_from_file_location()
now accept a
path-like object.
json¶
json.load()
and json.loads()
now support binary input. Encoded
JSON should be represented using either UTF-8, UTF-16, or UTF-32.
(Contributed by Serhiy Storchaka in issue 17909.)
os¶
A new close()
method allows explicitly closing a
scandir()
iterator. The scandir()
iterator now
supports the context manager protocol. If a scandir()
iterator is neither exhausted nor explicitly closed a ResourceWarning
will be emitted in its destructor.
(Contributed by Serhiy Storchaka in issue 25994.)
The Linux getrandom()
syscall (get random bytes) is now exposed as the new
os.getrandom()
function.
(Contributed by Victor Stinner, part of the PEP 524)
See the summary for PEP 519 for details on how the
os
and os.path
modules now support
path-like objects.
pickle¶
Objects that need calling __new__
with keyword arguments can now be pickled
using pickle protocols older than protocol version 4.
Protocol version 4 already supports this case. (Contributed by Serhiy
Storchaka in issue 24164.)
re¶
Added support of modifier spans in regular expressions. Examples:
'(?i:p)ython'
matches 'python'
and 'Python'
, but not 'PYTHON'
;
'(?i)g(?-i:v)r'
matches 'GvR'
and 'gvr'
, but not 'GVR'
.
(Contributed by Serhiy Storchaka in issue 433028.)
Match object groups can be accessed by __getitem__
, which is
equivalent to group()
. So mo['name']
is now equivalent to
mo.group('name')
. (Contributed by Eric Smith in issue 24454.)
readline¶
Added set_auto_history()
to enable or disable
automatic addition of input to the history list. (Contributed by
Tyler Crompton in issue 26870.)
rlcompleter¶
Private and special attribute names now are omitted unless the prefix starts with underscores. A space or a colon is added after some completed keywords. (Contributed by Serhiy Storchaka in issue 25011 and issue 25209.)
Names of most attributes listed by dir()
are now completed.
Previously, names of properties and slots which were not yet created on
an instance were excluded. (Contributed by Martin Panter in issue 25590.)
site¶
When specifying paths to add to sys.path
in a .pth file,
you may now specify file paths on top of directories (e.g. zip files).
(Contributed by Wolfgang Langner in issue 26587).
sqlite3¶
sqlite3.Cursor.lastrowid
now supports the REPLACE
statement.
(Contributed by Alex LordThorsen in issue 16864.)
socket¶
The ioctl()
function now supports the SIO_LOOPBACK_FAST_PATH
control code.
(Contributed by Daniel Stokes in issue 26536.)
The getsockopt()
constants SO_DOMAIN
,
SO_PROTOCOL
, SO_PEERSEC
, and SO_PASSSEC
are now supported.
(Contributed by Christian Heimes in issue 26907.)
The socket module now supports the address family
AF_ALG
to interface with Linux Kernel crypto API. ALG_*
,
SOL_ALG
and sendmsg_afalg()
were added.
(Contributed by Christian Heimes in issue 27744 with support from
Victor Stinner.)
socketserver¶
Servers based on the socketserver
module, including those
defined in http.server
, xmlrpc.server
and
wsgiref.simple_server
, now support the context manager
protocol.
(Contributed by Aviv Palivoda in issue 26404.)
The wfile
attribute of
StreamRequestHandler
classes now implements
the io.BufferedIOBase
writable interface. In particular,
calling write()
is now guaranteed to send the
data in full. (Contributed by Martin Panter in issue 26721.)
ssl¶
ssl
supports OpenSSL 1.1.0. The minimum recommend version is 1.0.2.
It has been tested with 0.9.8zc, 0.9.8zh and 1.0.1t as well as LibreSSL 2.3
and 2.4.
(Contributed by Christian Heimes in issue 26470.)
3DES has been removed from the default cipher suites and ChaCha20 Poly1305 cipher suites are now in the right position. (Contributed by Christian Heimes in issue 27850 and issue 27766.)
SSLContext
has better default configuration for options
and ciphers.
(Contributed by Christian Heimes in issue 28043.)
SSL session can be copied from one client-side connection to another
with SSLSession
. TLS session resumption can speed up
the initial handshake, reduce latency and improve performance
(Contributed by Christian Heimes in issue 19500 based on a draft by
Alex Warhawk.)
All constants and flags have been converted to IntEnum
and
IntFlags
.
(Contributed by Christian Heimes in issue 28025.)
Server and client-side specific TLS protocols for SSLContext
were added.
(Contributed by Christian Heimes in issue 28085.)
General resource ids (GEN_RID
) in subject alternative name extensions
no longer case a SystemError.
(Contributed by Christian Heimes in issue 27691.)
subprocess¶
subprocess.Popen
destructor now emits a ResourceWarning
warning
if the child process is still running. Use the context manager protocol (with
proc: ...
) or call explicitly the wait()
method to
read the exit status of the child process (Contributed by Victor Stinner in
issue 26741).
The subprocess.Popen
constructor and all functions that pass arguments
through to it now accept encoding and errors arguments. Specifying either
of these will enable text mode for the stdin, stdout and stderr streams.
telnetlib¶
Telnet
is now a context manager (contributed by
Stéphane Wirtel in issue 25485).
tkinter¶
Added methods trace_add()
,
trace_remove()
and trace_info()
in the tkinter.Variable
class. They replace old methods
trace_variable()
, trace()
,
trace_vdelete()
and
trace_vinfo()
that use obsolete Tcl commands and might
not work in future versions of Tcl.
(Contributed by Serhiy Storchaka in issue 22115).
traceback¶
Both the traceback module and the interpreter’s builtin exception display now abbreviate long sequences of repeated lines in tracebacks as shown in the following example:
>>> def f(): f()
...
>>> f()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 1, in f
File "<stdin>", line 1, in f
File "<stdin>", line 1, in f
[Previous line repeated 995 more times]
RecursionError: maximum recursion depth exceeded
(Contributed by Emanuel Barry in issue 26823.)
typing¶
The typing.ContextManager
class has been added for
representing contextlib.AbstractContextManager
.
(Contributed by Brett Cannon in issue 25609.)
unicodedata¶
The internal database has been upgraded to use Unicode 9.0.0. (Contributed by Benjamin Peterson.)
unittest.mock¶
The Mock
class has the following improvements:
- Two new methods,
Mock.assert_called()
andMock.assert_called_once()
to check if the mock object was called. (Contributed by Amit Saha in issue 26323.)
urllib.request¶
If a HTTP request has a file or iterable body (other than a
bytes object) but no Content-Length header, rather than
throwing an error, AbstractHTTPHandler
now
falls back to use chunked transfer encoding.
(Contributed by Demian Brecht and Rolf Krahl in issue 12319.)
urllib.robotparser¶
RobotFileParser
now supports the Crawl-delay
and
Request-rate
extensions.
(Contributed by Nikolay Bogoychev in issue 16099.)
warnings¶
A new optional source parameter has been added to the
warnings.warn_explicit()
function: the destroyed object which emitted a
ResourceWarning
. A source attribute has also been added to
warnings.WarningMessage
(contributed by Victor Stinner in
issue 26568 and issue 26567).
When a ResourceWarning
warning is logged, the tracemalloc
is now
used to try to retrieve the traceback where the detroyed object was allocated.
Example with the script example.py
:
import warnings
def func():
return open(__file__)
f = func()
f = None
Output of the command python3.6 -Wd -X tracemalloc=5 example.py
:
example.py:7: ResourceWarning: unclosed file <_io.TextIOWrapper name='example.py' mode='r' encoding='UTF-8'>
f = None
Object allocated at (most recent call first):
File "example.py", lineno 4
return open(__file__)
File "example.py", lineno 6
f = func()
The “Object allocated at” traceback is new and only displayed if
tracemalloc
is tracing Python memory allocations and if the
warnings
was already imported.
winreg¶
Added the 64-bit integer type REG_QWORD
.
(Contributed by Clement Rouault in issue 23026.)
winsound¶
Allowed keyword arguments to be passed to Beep
,
MessageBeep
, and PlaySound
(issue 27982).
xmlrpc.client¶
The module now supports unmarshalling additional data types used by
Apache XML-RPC implementation for numerics and None
.
(Contributed by Serhiy Storchaka in issue 26885.)
zipfile¶
A new ZipInfo.from_file()
class method
allows making a ZipInfo
instance from a filesystem file.
A new ZipInfo.is_dir()
method can be used
to check if the ZipInfo
instance represents a directory.
(Contributed by Thomas Kluyver in issue 26039.)
The ZipFile.open()
method can now be used to
write data into a ZIP file, as well as for extracting data.
(Contributed by Thomas Kluyver in issue 26039.)
zlib¶
The compress()
function now accepts keyword arguments.
(Contributed by Aviv Palivoda in issue 26243.)
fileinput¶
hook_encoded()
now supports the errors argument.
(Contributed by Joseph Hackman in issue 25788.)
Optimizations¶
- The ASCII decoder is now up to 60 times as fast for error handlers
surrogateescape
,ignore
andreplace
(Contributed by Victor Stinner in issue 24870). - The ASCII and the Latin1 encoders are now up to 3 times as fast for the
error handler
surrogateescape
(Contributed by Victor Stinner in issue 25227). - The UTF-8 encoder is now up to 75 times as fast for error handlers
ignore
,replace
,surrogateescape
,surrogatepass
(Contributed by Victor Stinner in issue 25267). - The UTF-8 decoder is now up to 15 times as fast for error handlers
ignore
,replace
andsurrogateescape
(Contributed by Victor Stinner in issue 25301). bytes % args
is now up to 2 times faster. (Contributed by Victor Stinner in issue 25349).bytearray % args
is now between 2.5 and 5 times faster. (Contributed by Victor Stinner in issue 25399).- Optimize
bytes.fromhex()
andbytearray.fromhex()
: they are now between 2x and 3.5x faster. (Contributed by Victor Stinner in issue 25401). - Optimize
bytes.replace(b'', b'.')
andbytearray.replace(b'', b'.')
: up to 80% faster. (Contributed by Josh Snider in issue 26574). - Allocator functions of the
PyMem_Malloc()
domain (PYMEM_DOMAIN_MEM
) now use the pymalloc memory allocator instead ofmalloc()
function of the C library. The pymalloc allocator is optimized for objects smaller or equal to 512 bytes with a short lifetime, and usemalloc()
for larger memory blocks. (Contributed by Victor Stinner in issue 26249). pickle.load()
andpickle.loads()
are now up to 10% faster when deserializing many small objects (Contributed by Victor Stinner in issue 27056).
- Passing keyword arguments to a function has an overhead in comparison with passing positional arguments. Now in extension functions implemented with using Argument Clinic this overhead is significantly decreased. (Contributed by Serhiy Storchaka in issue 27574).
- Optimized
glob()
andiglob()
functions in theglob
module; they are now about 3–6 times faster. (Contributed by Serhiy Storchaka in issue 25596). - Optimized globbing in
pathlib
by usingos.scandir()
; it is now about 1.5–4 times faster. (Contributed by Serhiy Storchaka in issue 26032).
Build and C API Changes¶
- Python now requires some C99 support in the toolchain to build. For more information, see PEP 7.
- Cross-compiling CPython with the Android NDK and the Android API level set to 21 (Android 5.0 Lollilop) or greater, runs successfully. While Android is not yet a supported platform, the Python test suite runs on the Android emulator with only about 16 tests failures. See the Android meta-issue issue 26865.
- The
--with-optimizations
configure flag has been added. Turning it on will activate LTO and PGO build support (when available). (Original patch by Alecsandru Patrascu of Intel in issue 26539.) - New
Py_FinalizeEx()
API which indicates if flushing buffered data failed (issue 5319). PyArg_ParseTupleAndKeywords()
now supports positional-only parameters. Positional-only parameters are defined by empty names. (Contributed by Serhiy Storchaka in issue 26282).PyTraceback_Print
method now abbreviates long sequences of repeated lines as"[Previous line repeated {count} more times]"
. (Contributed by Emanuel Barry in issue 26823.)
Deprecated¶
Deprecated Build Options¶
The --with-system-ffi
configure flag is now on by default on non-OSX UNIX
platforms. It may be disabled by using --without-system-ffi
, but using the
flag is deprecated and will not be accepted in Python 3.7. OSX is unaffected
by this change. Note that many OS distributors already use the
--with-system-ffi
flag when building their system Python.
New Keywords¶
async
and await
are not recommended to be used as variable, class,
function or module names. Introduced by PEP 492 in Python 3.5, they will
become proper keywords in Python 3.7.
Deprecated Python modules, functions and methods¶
importlib.machinery.SourceFileLoader.load_module()
andimportlib.machinery.SourcelessFileLoader.load_module()
are now deprecated. They were the only remaining implementations ofimportlib.abc.Loader.load_module()
inimportlib
that had not been deprecated in previous versions of Python in favour ofimportlib.abc.Loader.exec_module()
.- The
tkinter.tix
module is now deprecated.tkinter
users should usetkinter.ttk
instead.
Deprecated functions and types of the C API¶
- None yet.
Deprecated features¶
- The
pyvenv
script has been deprecated in favour ofpython3 -m venv
. This prevents confusion as to what Python interpreterpyvenv
is connected to and thus what Python interpreter will be used by the virtual environment. (Contributed by Brett Cannon in issue 25154.) - When performing a relative import, falling back on
__name__
and__path__
from the calling module when__spec__
or__package__
are not defined now raises anImportWarning
. (Contributed by Rose Ames in issue 25791.) - Unlike to other
dbm
implementations, thedbm.dumb
module creates database in'r'
and'w'
modes if it doesn’t exist and allows modifying database in'r'
mode. This behavior is now deprecated and will be removed in 3.8. (Contributed by Serhiy Storchaka in issue 21708.) - Undocumented support of general bytes-like objects
as paths in
os
functions,compile()
and similar functions is now deprecated. (Contributed by Serhiy Storchaka in issue 25791 and issue 26754.) - The undocumented
extra_path
argument to a distutils Distribution is now considered deprecated, will raise a warning during install if set. Support for this parameter will be dropped in a future Python release and likely earlier through third party tools. See issue 27919 for details. - A backslash-character pair that is not a valid escape sequence now generates a DeprecationWarning. Although this will eventually become a SyntaxError, that will not be for several Python releases. (Contributed by Emanuel Barry in issue 27364.)
- Inline flags
(?letters)
now should be used only at the start of the regular expression. Inline flags in the middle of the regular expression affects global flags in Pythonre
module. This is an exception to other regular expression engines that either apply flags to only part of the regular expression or treat them as an error. To avoid distinguishing inline flags in the middle of the regular expression now emit a deprecation warning. It will be an error in future Python releases. (Contributed by Serhiy Storchaka in issue 22493.) - SSL-related arguments like
certfile
,keyfile
andcheck_hostname
inftplib
,http.client
,imaplib
,poplib
, andsmtplib
have been deprecated in favor ofcontext
. (Contributed by Christian Heimes in issue 28022.) - A couple of protocols and functions of the
ssl
module are now deprecated. Some features will no longer be available in future versions of OpenSSL. Other features are deprecated in favor of a different API. (Contributed by Christian Heimes in issue 28022 and issue 26470.)
Deprecated Python behavior¶
- Raising the
StopIteration
exception inside a generator will now generate aDeprecationWarning
, and will trigger aRuntimeError
in Python 3.7. See PEP 479: Change StopIteration handling inside generators for details.
Removed¶
API and Feature Removals¶
inspect.getmoduleinfo()
was removed (was deprecated since CPython 3.3).inspect.getmodulename()
should be used for obtaining the module name for a given path.traceback.Ignore
class andtraceback.usage
,traceback.modname
,traceback.fullmodname
,traceback.find_lines_from_code
,traceback.find_lines
,traceback.find_strings
,traceback.find_executable_lines
methods were removed from thetraceback
module. They were undocumented methods deprecated since Python 3.2 and equivalent functionality is available from private methods.- The
tk_menuBar()
andtk_bindForTraversal()
dummy methods intkinter
widget classes were removed (corresponding Tk commands were obsolete since Tk 4.0). - The
open()
method of thezipfile.ZipFile
class no longer supports the'U'
mode (was deprecated since Python 3.4). Useio.TextIOWrapper
for reading compressed text files in universal newlines mode. - The undocumented
IN
,CDROM
,DLFCN
,TYPES
,CDIO
, andSTROPTS
modules have been removed. They had been available in the platform specificLib/plat-*/
directories, but were chronically out of date, inconsistently available across platforms, and unmaintained. The script that created these modules is still available in the source distribution at Tools/scripts/h2py.py.
Porting to Python 3.6¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Changes in ‘python’ Command Behavior¶
- The output of a special Python build with defined
COUNT_ALLOCS
,SHOW_ALLOC_COUNT
orSHOW_TRACK_COUNT
macros is now off by default. It can be re-enabled using the-X showalloccount
option. It now outputs tostderr
instead ofstdout
. (Contributed by Serhiy Storchaka in issue 23034.)
Changes in the Python API¶
sqlite3
no longer implicitly commit an open transaction before DDL statements.On Linux,
os.urandom()
now blocks until the system urandom entropy pool is initialized to increase the security.When
importlib.abc.Loader.exec_module()
is defined,importlib.abc.Loader.create_module()
must also be defined.PyErr_SetImportError()
now setsTypeError
when its msg argument is not set. Previously onlyNULL
was returned.The format of the
co_lnotab
attribute of code objects changed to support negative line number delta. By default, Python does not emit bytecode with negative line number delta. Functions usingframe.f_lineno
,PyFrame_GetLineNumber()
orPyCode_Addr2Line()
are not affected. Functions decoding directlyco_lnotab
should be updated to use a signed 8-bit integer type for the line number delta, but it’s only required to support applications using negative line number delta. SeeObjects/lnotab_notes.txt
for theco_lnotab
format and how to decode it, and see the PEP 511 for the rationale.The functions in the
compileall
module now return booleans instead of1
or0
to represent success or failure, respectively. Thanks to booleans being a subclass of integers, this should only be an issue if you were doing identity checks for1
or0
. See issue 25768.Reading the
port
attribute ofurllib.parse.urlsplit()
andurlparse()
results now raisesValueError
for out-of-range values, rather than returningNone
. See issue 20059.The
imp
module now raises aDeprecationWarning
instead ofPendingDeprecationWarning
.The following modules have had missing APIs added to their
__all__
attributes to match the documented APIs:calendar
,cgi
,csv
,ElementTree
,enum
,fileinput
,ftplib
,logging
,mailbox
,mimetypes
,optparse
,plistlib
,smtpd
,subprocess
,tarfile
,threading
andwave
. This means they will export new symbols whenimport *
is used. See issue 23883.When performing a relative import, if
__package__
does not compare equal to__spec__.parent
thenImportWarning
is raised. (Contributed by Brett Cannon in issue 25791.)When a relative import is performed and no parent package is known, then
ImportError
will be raised. Previously,SystemError
could be raised. (Contributed by Brett Cannon in issue 18018.)Servers based on the
socketserver
module, including those defined inhttp.server
,xmlrpc.server
andwsgiref.simple_server
, now only catch exceptions derived fromException
. Therefore if a request handler raises an exception likeSystemExit
orKeyboardInterrupt
,handle_error()
is no longer called, and the exception will stop a single-threaded server. (Contributed by Martin Panter in issue 23430.)spwd.getspnam()
now raises aPermissionError
instead ofKeyError
if the user doesn’t have privileges.The
socket.socket.close()
method now raises an exception if an error (e.g. EBADF) was reported by the underlying system call. See issue 26685.The decode_data argument for
smtpd.SMTPChannel
andsmtpd.SMTPServer
constructors is nowFalse
by default. This means that the argument passed toprocess_message()
is now a bytes object by default, andprocess_message()
will be passed keyword arguments. Code that has already been updated in accordance with the deprecation warning generated by 3.5 will not be affected.All optional parameters of the
dump()
,dumps()
,load()
andloads()
functions andJSONEncoder
andJSONDecoder
class constructors in thejson
module are now keyword-only. (Contributed by Serhiy Storchaka in issue 18726.)As part of PEP 487, the handling of keyword arguments passed to
type
(other than the metaclass hint,metaclass
) is now consistently delegated toobject.__init_subclass__()
. This means thattype.__new__()
andtype.__init__()
both now accept arbitrary keyword arguments, butobject.__init_subclass__()
(which is called fromtype.__new__()
) will reject them by default. Custom metaclasses accepting additional keyword arguments will need to adjust their calls totype.__new__()
(whether direct or viasuper
) accordingly.In
distutils.command.sdist.sdist
, thedefault_format
attribute has been removed and is no longer honored. Instead, the gzipped tarfile format is the default on all platforms and no platform-specific selection is made. In environments where distributions are built on Windows and zip distributions are required, configure the project with asetup.cfg
file containing the following:[sdist] formats=zip
This behavior has also been backported to earlier Python versions by Setuptools 26.0.0.
In the
urllib.request
module and thehttp.client.HTTPConnection.request()
method, if no Content-Length header field has been specified and the request body is a file object, it is now sent with HTTP 1.1 chunked encoding. If a file object has to be sent to a HTTP 1.0 server, the Content-Length value now has to be specified by the caller. See issue 12319.
Changes in the C API¶
PyMem_Malloc()
allocator family now uses the pymalloc allocator rather than systemmalloc()
. Applications callingPyMem_Malloc()
without holding the GIL can now crash. Set thePYTHONMALLOC
environment variable todebug
to validate the usage of memory allocators in your application. See issue 26249.Py_Exit()
(and the main interpreter) now override the exit status with 120 if flushing buffered data failed. See issue 5319.