This article explains the new features in Python 3.6, compared to 3.5. Python 3.6 was released on December 23, 2016. For full details, see the changelog.

A python36.zip file now works as a landmark to infer PYTHONHOME . See the documentation for more information.

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.

python.exe and pythonw.exe have been marked as long-path aware, which means that the 260 character path limit may no longer apply. See removing the MAX_PATH limitation for details.

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.

The hashlib module received support for the BLAKE2, SHA-3 and SHAKE hash algorithms and the scrypt() key derivation function.

The default settings and feature set of the ssl module have been improved.

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.

The new secrets module has been added to simplify the generation of cryptographically strong pseudo-random numbers suitable for managing secrets such as account authentication, tokens, and similar.

The tracemalloc module has been significantly reworked and is now used to provide better output for ResourceWarning as well as provide better diagnostics for memory allocation errors. See the PYTHONMALLOC section for more information.

A new file system path protocol has been implemented to support path-like objects . All standard library functions operating on paths have been updated to work with the new protocol.

The asyncio module has received new features, significant usability and performance improvements, and a fair amount of bug fixes. Starting with Python 3.6 the asyncio module is no longer provisional and its API is considered stable.

The new PYTHONMALLOC environment variable can now be used to debug the interpreter memory allocation and access errors.

The order of elements in **kwargs now corresponds to the order in which keyword arguments were passed to the function.

Customization of class creation has been simplified with the new protocol .

The dict type has been reimplemented to use a more compact representation based on a proposal by Raymond Hettinger and similar to the PyPy dict implementation . This resulted in dictionaries using 20% to 25% less memory when compared to Python 3.5.

(Contributed by Łukasz Langa in bpo-21590 , based on patches by Jesús Cea Avión, David Malcolm, and Nikhil Benesch.)

The current implementation is tested on Linux and macOS. Additional markers may be added in the future.

More details in Instrumenting CPython with DTrace and SystemTap .

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.

Python can now be built --with-dtrace which enables static markers for the following events in the interpreter:

Example of fatal error on buffer overflow using python3.6 -X tracemalloc=5 (store 5 frames in traces):

On error, the debug hooks on Python memory allocators now use the tracemalloc module to get the traceback where a memory block was allocated.

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 . This is helpful when using external memory debuggers like Valgrind on a Python compiled in release mode.

See the PyMem_SetupDebugHooks() function for debug hooks on Python memory allocators.

Checking if the GIL is held is also a new feature of Python 3.6.

Check that the GIL is held when allocator functions of PYMEM_DOMAIN_OBJ (ex: PyObject_Malloc() ) and PYMEM_DOMAIN_MEM (ex: PyMem_Malloc() ) domains are called.

Detect violations of the Python memory allocator API. For example, PyObject_Free() called on a memory block allocated by PyMem_Malloc() .

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:

The new PYTHONMALLOC environment variable allows setting the Python memory allocators and installing debug hooks.

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.

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.

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.

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).

The dict type now uses a “compact” representation based on a proposal by Raymond Hettinger which was first implemented by PyPy . The memory usage of the new dict() is between 20% and 25% smaller compared to Python 3.5.

**kwargs in a function signature is now guaranteed to be an insertion-order-preserving mapping.

Also, the effective default class execution namespace (returned from type.__prepare__() ) is now an insertion-order-preserving mapping.

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.

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 PYTHONLEGACYWINDOWSSTDIO .

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.

See PEP 529 for more information and discussion of code modifications that may be required.

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() .

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' .

Representing filesystem paths is best performed with str (Unicode) rather than bytes. However, there are some situations where using bytes is sufficient and correct.

The values of the fold attribute have the value 0 for all instances except those that represent the second (chronologically) moment in time in an ambiguous case.

PEP 495 adds the new fold attribute to instances of datetime.datetime and datetime.time classes to differentiate between two moments in time for which local times are the same:

In most world locations, there have been and will be times when local clocks are moved back. In those times, intervals are introduced in which local clocks show the same time twice in the same day. In these situations, the information displayed on a local clock (or stored in a Python datetime instance) is insufficient to identify a particular moment in time.

Here are some examples of how the new interface allows for pathlib.Path to be used more easily and transparently with pre-existing code:

The hope 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).

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, and most other functions and classes in the standard library. The os.DirEntry class and relevant classes in pathlib have also been updated to implement os.PathLike .

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.

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.

# this is the new initializer:

PEP 487 extends the descriptor protocol to include the new optional __set_name__() method. Whenever a new class is defined, the new method will be called on all descriptors included in the definition, providing them with a reference to the class being defined and the name given to the descriptor within the class namespace. In other words, instances of descriptors can now know the attribute name of the descriptor in the owner class:

In order to allow zero-argument super() calls to work correctly from __init_subclass__() implementations, custom metaclasses must ensure that the new __classcell__ namespace entry is propagated to type.__new__ (as described in Creating the class object ).

It is now possible to customize subclass creation without using a metaclass. The new __init_subclass__ classmethod will be called on the base class whenever a new subclass is created:

Additionally, await expressions are supported in all kinds of comprehensions:

PEP 530 adds support for using async for in list, set, dict comprehensions and generator expressions:

The new syntax allows for faster and more concise code.

"""Yield numbers from 0 to *to* every *delay* seconds."""

PEP 492 introduced support for native coroutines and async / await syntax to Python 3.5. A notable limitation of the Python 3.5 implementation is that it was not possible to use await and yield in the same function body. In Python 3.6 this restriction has been lifted, making it possible to define asynchronous generators:

The string formatting language also now has support for the '_' option to signal the use of an underscore for a thousands separator for floating point presentation types and for integer presentation type 'd' . For integer presentation types 'b' , 'o' , 'x' , and 'X' , underscores will be inserted every 4 digits:

Single underscores are allowed between digits and after any base specifier. Leading, trailing, or multiple underscores in a row are not allowed.

PEP 515 adds the ability to use underscores in numeric literals for improved readability. For example:

Tools that use or will use the new syntax: mypy , pytype , PyCharm, etc.

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.

Just as for function annotations, the Python interpreter does not attach any particular meaning to variable annotations and only stores them in the __annotations__ attribute of a class or module.

PEP 484 introduced the standard for type annotations of function parameters, a.k.a. type hints. This PEP adds syntax to Python for annotating the types of variables including class variables and instance variables:

'He said his name is Fred.'

"He said his name is

Formatted string literals are prefixed with 'f' and 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:

Class methods relying on zero-argument super() will now work correctly when called from metaclass methods during class creation. (Contributed by Martin Teichmann in bpo-23722 .)

Import now raises the new exception ModuleNotFoundError (subclass of ImportError ) when it cannot find a module. Code that currently checks for ImportError (in try-except) will still work. (Contributed by Eric Snow in bpo-15767 .)

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 bpo-26823 .)

It is now possible to set a special method to None to indicate that the corresponding operation is not available. For example, if a class sets __iter__() to None , the class is not iterable. (Contributed by Andrew Barnert and Ivan Levkivskyi in bpo-25958 .)

A global or nonlocal statement must now textually appear before the first use of the affected name in the same scope. Previously this was a SyntaxWarning .

Some smaller changes made to the core Python language are:

Note that the pseudo-random generators in the random module should NOT be used for security purposes. Use secrets on Python 3.6+ and os.urandom() on Python 3.5 and earlier.

The main purpose of the new secrets module is to provide an obvious way to reliably generate cryptographically strong pseudo-random values suitable for managing secrets, such as account authentication, tokens, and similar.

Improved Modules¶

array¶ Exhausted iterators of array.array will now stay exhausted even if the iterated array is extended. This is consistent with the behavior of other mutable sequences. Contributed by Serhiy Storchaka in bpo-26492.

ast¶ The new ast.Constant AST node has been added. It can be used by external AST optimizers for the purposes of constant folding. Contributed by Victor Stinner in bpo-26146.

asyncio¶ Starting with Python 3.6 the asyncio module is no longer provisional and its API is considered stable. Notable changes in the asyncio module since Python 3.5.0 (all backported to 3.5.x due to the provisional status): The get_event_loop() function has been changed to always return the currently running loop when called from coroutines and callbacks. (Contributed by Yury Selivanov in bpo-28613.)

The ensure_future() function and all functions that use it, such as loop.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 faster asyncio.Future implementation. (Contributed by Yury Selivanov in bpo-27041.)

New loop.get_exception_handler() method to get the current exception handler. (Contributed by Yury Selivanov in bpo-27040.)

New StreamReader.readuntil() method to read data from the stream until a separator bytes sequence appears. (Contributed by Mark Korenberg.)

The performance of StreamReader.readexactly() has been improved. (Contributed by Mark Korenberg in bpo-28370.)

The loop.getaddrinfo() method is optimized to avoid calling the system getaddrinfo function if the address is already resolved. (Contributed by A. Jesse Jiryu Davis.)

The loop.stop() method has been changed to stop the loop immediately after the current iteration. Any new callbacks scheduled as a result of the last iteration will be discarded. (Contributed by Guido van Rossum in bpo-25593.)

Future.set_exception will now raise TypeError when passed an instance of the StopIteration exception. (Contributed by Chris Angelico in bpo-26221.)

New loop.connect_accepted_socket() method to be used by servers that accept connections outside of asyncio, but that use asyncio to handle them. (Contributed by Jim Fulton in bpo-27392.)

TCP_NODELAY flag is now set for all TCP transports by default. (Contributed by Yury Selivanov in bpo-27456.)

New loop.shutdown_asyncgens() to properly close pending asynchronous generators before closing the loop. (Contributed by Yury Selivanov in bpo-28003.)

Future and Task classes now have an optimized C implementation which makes asyncio code up to 30% faster. (Contributed by Yury Selivanov and INADA Naoki in bpo-26081 and bpo-28544.)

binascii¶ The b2a_base64() function now accepts an optional newline keyword argument to control whether the newline character is appended to the return value. (Contributed by Victor Stinner in bpo-25357.)

cmath¶ The new cmath.tau (τ) constant has been added. (Contributed by Lisa Roach in bpo-12345, see PEP 628 for details.) New constants: cmath.inf and cmath.nan to match math.inf and math.nan , and also cmath.infj and cmath.nanj to match the format used by complex repr. (Contributed by Mark Dickinson in bpo-23229.)

collections¶ The new Collection abstract base class has been added to represent sized iterable container classes. (Contributed by Ivan Levkivskyi, docs by Neil Girdhar in bpo-27598.) The new Reversible abstract base class represents iterable classes that also provide the __reversed__() method. (Contributed by Ivan Levkivskyi in bpo-25987.) The new AsyncGenerator abstract base class represents asynchronous generators. (Contributed by Yury Selivanov in bpo-28720.) The namedtuple() function now accepts an optional keyword argument module, which, when specified, is used for the __module__ attribute of the returned named tuple class. (Contributed by Raymond Hettinger in bpo-17941.) The verbose and rename arguments for namedtuple() are now keyword-only. (Contributed by Raymond Hettinger in bpo-25628.) Recursive collections.deque instances can now be pickled. (Contributed by Serhiy Storchaka in bpo-26482.)

concurrent.futures¶ The ThreadPoolExecutor class constructor now accepts an optional thread_name_prefix argument to make it possible to customize the names of the threads created by the pool. (Contributed by Gregory P. Smith in bpo-27664.)

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 bpo-25609.)

decimal¶ New Decimal.as_integer_ratio() method that returns a pair (n, d) of integers that represent the given Decimal instance as a fraction, in lowest terms and with a positive denominator: >>> Decimal ( '-3.14' ) . as_integer_ratio () (-157, 50) (Contributed by Stefan Krah amd Mark Dickinson in bpo-25928.)

distutils¶ 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 bpo-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 bpo-24277.) The email.mime classes now all accept an optional policy keyword. (Contributed by Berker Peksag in bpo-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 bpo-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. (Contributed by Steve Dower in bpo-27959.)

enum¶ Two new enumeration base classes have been added to the enum module: Flag and IntFlags . Both are used to define constants that can be combined using the bitwise operators. (Contributed by Ethan Furman in bpo-23591.) Many standard library modules have been updated to use the IntFlags class for their constants. The new enum.auto value can be used to assign values to enum members automatically: >>> from enum import Enum , auto >>> class Color ( Enum ): ... red = auto () ... blue = auto () ... green = auto () ... >>> list ( Color ) [<Color.red: 1>, <Color.blue: 2>, <Color.green: 3>]

faulthandler¶ On Windows, the faulthandler module now installs a handler for Windows exceptions: see faulthandler.enable() . (Contributed by Victor Stinner in bpo-23848.)

fileinput¶ hook_encoded() now supports the errors argument. (Contributed by Joseph Hackman in bpo-25788.)

hashlib¶ hashlib supports OpenSSL 1.1.0. The minimum recommend version is 1.0.2. (Contributed by Christian Heimes in bpo-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 bpo-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 bpo-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 bpo-27928.)

http.client¶ HTTPConnection.request() and endheaders() both now support chunked encoding request bodies. (Contributed by Demian Brecht and Rolf Krahl in bpo-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 bpo-24225. Most idlelib patches since have been and will be part of the process.) In compensation, the eventual result with be that some idlelib classes will be easier to use, with better APIs and docstrings explaining them. Additional useful information will be added to idlelib when available. New in 3.6.2: Multiple fixes for autocompletion. (Contributed by Louie Lu in bpo-15786.) New in 3.6.3: Module Browser (on the File menu, formerly called Class Browser), now displays nested functions and classes in addition to top-level functions and classes. (Contributed by Guilherme Polo, Cheryl Sabella, and Terry Jan Reedy in bpo-1612262.) The IDLE features formerly implemented as extensions have been reimplemented as normal features. Their settings have been moved from the Extensions tab to other dialog tabs. (Contributed by Charles Wohlganger and Terry Jan Reedy in bpo-27099.) The Settings dialog (Options, Configure IDLE) has been partly rewritten to improve both appearance and function. (Contributed by Cheryl Sabella and Terry Jan Reedy in multiple issues.) New in 3.6.4: The font sample now includes a selection of non-Latin characters so that users can better see the effect of selecting a particular font. (Contributed by Terry Jan Reedy in bpo-13802.) The sample can be edited to include other characters. (Contributed by Serhiy Storchaka in bpo-31860.) New in 3.6.6: Editor code context option revised. Box displays all context lines up to maxlines. Clicking on a context line jumps the editor to that line. Context colors for custom themes is added to Highlights tab of Settings dialog. (Contributed by Cheryl Sabella and Terry Jan Reedy in bpo-33642, bpo-33768, and bpo-33679.) On Windows, a new API call tells Windows that tk scales for DPI. On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary unchanged, and a monitor resolution greater than 96 DPI, this should make text and lines sharper. It should otherwise have no effect. (Contributed by Terry Jan Reedy in bpo-33656.) New in 3.6.7: Output over N lines (50 by default) is squeezed down to a button. N can be changed in the PyShell section of the General page of the Settings dialog. Fewer, but possibly extra long, lines can be squeezed by right clicking on the output. Squeezed output can be expanded in place by double-clicking the button or into the clipboard or a separate window by right-clicking the button. (Contributed by Tal Einat in bpo-1529353.)

importlib¶ Import now raises the new exception ModuleNotFoundError (subclass of ImportError ) when it cannot find a module. Code that current checks for ImportError (in try-except) will still work. (Contributed by Eric Snow in bpo-15767.) 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.

inspect¶ The inspect.signature() function now reports the implicit .0 parameters generated by the compiler for comprehension and generator expression scopes as if they were positional-only parameters called implicit0 . (Contributed by Jelle Zijlstra in bpo-19611.) To reduce code churn when upgrading from Python 2.7 and the legacy inspect.getargspec() API, the previously documented deprecation of inspect.getfullargspec() has been reversed. While this function is convenient for single/source Python 2/3 code bases, the richer inspect.signature() interface remains the recommended approach for new code. (Contributed by Nick Coghlan in bpo-27172)

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 bpo-17909.)

logging¶ The new WatchedFileHandler.reopenIfNeeded() method has been added to add the ability to check if the log file needs to be reopened. (Contributed by Marian Horban in bpo-24884.)

math¶ The tau (τ) constant has been added to the math and cmath modules. (Contributed by Lisa Roach in bpo-12345, see PEP 628 for details.)

multiprocessing¶ Proxy Objects returned by multiprocessing.Manager() can now be nested. (Contributed by Davin Potts in bpo-6766.)

pathlib¶ pathlib now supports path-like objects. (Contributed by Brett Cannon in bpo-27186.) See the summary of PEP 519 for details.

pdb¶ The Pdb class constructor has a new optional readrc argument to control whether .pdbrc files should be read.

pickle¶ Objects that need __new__ called 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 bpo-24164.)

pydoc¶ The pydoc module has learned to respect the MANPAGER environment variable. (Contributed by Matthias Klose in bpo-8637.) help() and pydoc can now list named tuple fields in the order they were defined rather than alphabetically. (Contributed by Raymond Hettinger in bpo-24879.)

random¶ The new choices() function returns a list of elements of specified size from the given population with optional weights. (Contributed by Raymond Hettinger in bpo-18844.)

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 bpo-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 bpo-24454.) Match objects now support index-like objects as group indices. (Contributed by Jeroen Demeyer and Xiang Zhang in bpo-27177.)

readline¶ Added set_auto_history() to enable or disable automatic addition of input to the history list. (Contributed by Tyler Crompton in bpo-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 bpo-25011 and bpo-25209.)

shlex¶ The shlex has much improved shell compatibility through the new punctuation_chars argument to control which characters are treated as punctuation. (Contributed by Vinay Sajip in bpo-1521950.)

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 bpo-26587).

sqlite3¶ sqlite3.Cursor.lastrowid now supports the REPLACE statement. (Contributed by Alex LordThorsen in bpo-16864.)

socket¶ The ioctl() function now supports the SIO_LOOPBACK_FAST_PATH control code. (Contributed by Daniel Stokes in bpo-26536.) The getsockopt() constants SO_DOMAIN , SO_PROTOCOL , SO_PEERSEC , and SO_PASSSEC are now supported. (Contributed by Christian Heimes in bpo-26907.) The setsockopt() now supports the setsockopt(level, optname, None, optlen: int) form. (Contributed by Christian Heimes in bpo-27744.) 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 bpo-27744 with support from Victor Stinner.) New Linux constants TCP_USER_TIMEOUT and TCP_CONGESTION were added. (Contributed by Omar Sandoval, issue: 26273 ).

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 bpo-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 bpo-26721.)

ssl¶ ssl supports OpenSSL 1.1.0. The minimum recommend version is 1.0.2. (Contributed by Christian Heimes in bpo-26470.) 3DES has been removed from the default cipher suites and ChaCha20 Poly1305 cipher suites have been added. (Contributed by Christian Heimes in bpo-27850 and bpo-27766.) SSLContext has better default configuration for options and ciphers. (Contributed by Christian Heimes in bpo-28043.) SSL session can be copied from one client-side connection to another with the new SSLSession class. TLS session resumption can speed up the initial handshake, reduce latency and improve performance (Contributed by Christian Heimes in bpo-19500 based on a draft by Alex Warhawk.) The new get_ciphers() method can be used to get a list of enabled ciphers in order of cipher priority. All constants and flags have been converted to IntEnum and IntFlags . (Contributed by Christian Heimes in bpo-28025.) Server and client-side specific TLS protocols for SSLContext were added. (Contributed by Christian Heimes in bpo-28085.) Added 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 in bpo-34670.)

statistics¶ A new harmonic_mean() function has been added. (Contributed by Steven D’Aprano in bpo-27181.)

struct¶ struct now supports IEEE 754 half-precision floats via the 'e' format specifier. (Contributed by Eli Stevens, Mark Dickinson in bpo-11734.)

subprocess¶ subprocess.Popen destructor now emits a ResourceWarning warning if the child process is still running. Use the context manager protocol ( with proc: ... ) or explicitly call the wait() method to read the exit status of the child process. (Contributed by Victor Stinner in bpo-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. (Contributed by Steve Dower in bpo-6135.)

sys¶ The new getfilesystemencodeerrors() function returns the name of the error mode used to convert between Unicode filenames and bytes filenames. (Contributed by Steve Dower in bpo-27781.) On Windows the return value of the getwindowsversion() function now includes the platform_version field which contains the accurate major version, minor version and build number of the current operating system, rather than the version that is being emulated for the process (Contributed by Steve Dower in bpo-27932.)

telnetlib¶ Telnet is now a context manager (contributed by Stéphane Wirtel in bpo-25485).

time¶ The struct_time attributes tm_gmtoff and tm_zone are now available on all platforms.

timeit¶ The new Timer.autorange() convenience method has been added to call Timer.timeit() repeatedly so that the total run time is greater or equal to 200 milliseconds. (Contributed by Steven D’Aprano in bpo-6422.) timeit now warns when there is substantial (4x) variance between best and worst times. (Contributed by Serhiy Storchaka in bpo-23552.)

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 bpo-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 bpo-26823.)

tracemalloc¶ The tracemalloc module now supports tracing memory allocations in multiple different address spaces. The new DomainFilter filter class has been added to filter block traces by their address space (domain). (Contributed by Victor Stinner in bpo-26588.)

typing¶ Since the typing module is provisional, all changes introduced in Python 3.6 have also been backported to Python 3.5.x. The typing module has a much improved support for generic type aliases. For example Dict[str, Tuple[S, T]] is now a valid type annotation. (Contributed by Guido van Rossum in Github #195.) The typing.ContextManager class has been added for representing contextlib.AbstractContextManager . (Contributed by Brett Cannon in bpo-25609.) The typing.Collection class has been added for representing collections.abc.Collection . (Contributed by Ivan Levkivskyi in bpo-27598.) The typing.ClassVar type construct has been added to mark class variables. As introduced in PEP 526, a variable annotation wrapped in ClassVar indicates that a given attribute is intended to be used as a class variable and should not be set on instances of that class. (Contributed by Ivan Levkivskyi in Github #280.) A new TYPE_CHECKING constant that is assumed to be True by the static type chekers, but is False at runtime. (Contributed by Guido van Rossum in Github #230.) A new NewType() helper function has been added to create lightweight distinct types for annotations: from typing import NewType UserId = NewType ( 'UserId' , int ) some_id = UserId ( 524313 ) The static type checker will treat the new type as if it were a subclass of the original type. (Contributed by Ivan Levkivskyi in Github #189.)

unicodedata¶ The unicodedata module now uses data from Unicode 9.0.0. (Contributed by Benjamin Peterson.)

unittest.mock¶ The Mock class has the following improvements: Two new methods, Mock.assert_called() and Mock.assert_called_once() to check if the mock object was called. (Contributed by Amit Saha in bpo-26323.)

The Mock.reset_mock() method now has two optional keyword only arguments: return_value and side_effect. (Contributed by Kushal Das in bpo-21271.)

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 bpo-12319.)

urllib.robotparser¶ RobotFileParser now supports the Crawl-delay and Request-rate extensions. (Contributed by Nikolay Bogoychev in bpo-16099.)

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 bpo-22829.)

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 bpo-26568 and bpo-26567). When a ResourceWarning warning is logged, the tracemalloc module is now used to try to retrieve the traceback where the destroyed object was allocated. Example with the script example.py : import warnings def func (): return open ( __file__ ) f = func () f = None Output of the command python3.6 -Wd -X tracemalloc=5 example.py : example . py : 7 : ResourceWarning : unclosed file < _io . TextIOWrapper name = 'example.py' mode = 'r' encoding = 'UTF-8' > f = None Object allocated at ( most recent call first ): File "example.py" , lineno 4 return open ( __file__ ) File "example.py" , lineno 6 f = func () The “Object allocated at” traceback is new and is only displayed if tracemalloc is tracing Python memory allocations and if the warnings module was already imported.

winreg¶ Added the 64-bit integer type REG_QWORD . (Contributed by Clement Rouault in bpo-23026.)

winsound¶ Allowed keyword arguments to be passed to Beep , MessageBeep , and PlaySound (bpo-27982).

xmlrpc.client¶ The xmlrpc.client module now supports unmarshalling additional data types used by the Apache XML-RPC implementation for numerics and None . (Contributed by Serhiy Storchaka in bpo-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 bpo-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 bpo-26039.)