Python 3.6.md

原文：What's New in Python

Python 3.6新特性

发布版本：	3.6.0b2
日期：	2016年10月11日

本文介绍了与3.5相比，Python 3.6的新特性。

有关详情，见更新日志。

注意

抢鲜用户应该注意，本文档目前还处于草稿阶段。随着Python 3.6的发布，将会大幅度更新，因此，甚至是在阅读早期版本后，都值得回来再看看。

摘要 - 版本亮点

新语法特性：

• 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.
• PEP 498: 格式化字符串
• PEP 515: 数字文本中的下划线
• PEP 526: 变量注解语法
• PEP 525: 异步生成器
• PEP 530: 异步推导式

标准库改进：

安全性改进：

• 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 and ssl 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 and scrypt() key derivation function.

Windows改进：

• 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 and pythonw.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 infer PYTHONHOME. See the documentation for more information.

新的内置特性：

• PEP 520: Preserving Class Attribute Definition Order
• PEP 468: Preserving Keyword Argument Order

Python 3.6中实现的PEP完整列表：

• 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

新特性

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.

又见

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.

又见

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__()](https:/ /docs.python.org/3.6/library/os.html#os.PathLike.fspath "os.PathLike.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()](htt ps://docs.python.org/3.6/c-api/unicode.html#c.PyUnicode_FSConverter "PyUnicode_FSConverter" ) and [PyUnicode_FSConverter()](https://docs.python. org/3.6/c-api/unicode.html#c.PyUnicode_FSConverter "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.)

又见

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](https://docs.python.org/3.6/refer ence/lexical_analysis.html#f-strings).

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.

又见

PEP 526 - Syntax for variable annotations.

PEP written by Ryan Gonzalez, Philip House, Ivan Levkivskyi, Lisa Roach, and Guido van Rossum. Implemented by Ivan Levkivskyi.

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

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.getfilesy stemencoding()](https://docs.python.org/3.6/library/sys.html#sys.getfilesyste mencoding "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](https://docs.python. org/3.6/using/cmdline.html#envvar-PYTHONLEGACYWINDOWSFSENCODING) or call [sys ._enablelegacywindowsfsencoding()](https://docs.python.org/3.6/library/sys.ht ml#sys._enablelegacywindowsfsencoding "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](https://docs.python.org/3.6/reference/datamodel.html#class- customization) and [Implementing Descriptors](https://docs.python.org/3.6/refe rence/datamodel.html#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](https://docs.py thon.org/3.6/using/cmdline.html#envvar-PYTHONLEGACYWINDOWSIOENCODING).

又见

PEP 528 - Change Windows console encoding to UTF-8

PEP written and implemented by Steve Dower.

PYTHONMALLOC environment variable

The new [PYTHONMALLOC](https://docs.python.org/3.6/using/cmdline.html #envvar-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 by PyMem_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()) and PYMEM_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()](https://docs.python.org/3.6/c-api/memory.h tml#c.PyMem_SetupDebugHooks "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](https://docs.python.org/3.6/library/tracemalloc.html#module- tracemalloc "tracemalloc: Trace memory allocations." ) 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](https://docs .python.org/3.6/howto/instrumentation.html#instrumentation).

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.

又见

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.

又见

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 new dict() 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 of ImportError) 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](https://docs.python.org/3.6/library/asyncio.html#module- asyncio "asyncio: Asynchronous I/O, event loop, coroutines and tasks." ) module is [provisional](https://docs.python.org/3.6/glossary.html#term- provisional-api), 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 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.)
• 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 system getaddrinfo function if the address is already resolved. (Contributed by A. Jesse Jiryu Davis.)

contextlib

The [contextlib.AbstractContextManager](https://docs.python.org/3.6/library/ contextlib.html#contextlib.AbstractContextManager "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.Context Manager](https://docs.python.org/3.6/library/typing.html#typing.ContextManage r "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()](https://docs.python.org/3.6/library/datetime.html# datetime.datetime.strftime "datetime.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](https://docs.python.org/3.6/library/email.mime.html#module- email.mime "email.mime: Build MIME messages." ) classes now all accept an optional policy keyword. (Contributed by Berker Peksag in issue 27331.)

The [DecodedGenerator](https://docs.python.org/3.6/library/email.generator.h tml#email.generator.DecodedGenerator "email.generator.DecodedGenerator" ) now supports the policy keyword.

There is a new [policy](https://docs.python.org/3.6/library/email.policy.html#module- email.policy "email.policy: Controlling the parsing and generating of messages" ) attribute, [message_factory](https://docs.python.org/3.6/library /email.policy.html#email.policy.Policy.message_factory "email.policy.Policy.message_factory" ), that controls what class is used by default when the parser creates new message objects. For the [email.policy.co mpat32](https://docs.python.org/3.6/library/email.policy.html#email.policy.co mpat32 "email.policy.compat32" ) policy this is [Message](https://docs.pytho n.org/3.6/library/email.compat32-message.html#email.message.Message "email.message.Message" ), for the new policies it is [EmailMessage](https:/ /docs.python.org/3.6/library/email.message.html#email.message.EmailMessage "email.message.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](https://docs.python.org/3.6/library/faulthandler.html#module- faulthandler "faulthandler: Dump the Python traceback." ) module now installs a handler for Windows exceptions: see [faulthandler.enable()](https://docs.p ython.org/3.6/library/faulthandler.html#faulthandler.enable "faulthandler.enable" ). (Contributed by Victor Stinner in issue 23848.)

hashlib

[hashlib](https://docs.python.org/3.6/library/hashlib-blake2.html#module- hashlib "hashlib: BLAKE2 hash function for Python" ) 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()](https://docs.python.org/3.6/library/hashlib- blake2.html#hashlib.blake2b "hashlib.blake2b" ) and [blake2s()](https://docs.python.org/3.6/library/hashlib- blake2.html#hashlib.blake2s "hashlib.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()](https://docs.python.org/3.6/library/http.client.h tml#http.client.HTTPConnection.request "http.client.HTTPConnection.request" ) and [endheaders()](https://docs.python.org/3.6/library/http.client.html#http .client.HTTPConnection.endheaders "http.client.HTTPConnection.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](https://docs.python.org/3.6/library/importlib.ht ml#importlib.util.LazyLoader "importlib.util.LazyLoader" ) now calls [create_ module()](https://docs.python.org/3.6/library/importlib.html#importlib.abc.Lo ader.create_module "importlib.abc.Loader.create_module" ) on the wrapped loader, removing the restriction that [importlib.machinery.BuiltinImporter]( https://docs.python.org/3.6/library/importlib.html#importlib.machinery.Builtin Importer "importlib.machinery.BuiltinImporter" ) and [importlib.machinery.Ext ensionFileLoader](https://docs.python.org/3.6/library/importlib.html#importli b.machinery.ExtensionFileLoader "importlib.machinery.ExtensionFileLoader" ) couldn't be used with [importlib.util.LazyLoader](https://docs.python.org/3. 6/library/importlib.html#importlib.util.LazyLoader "importlib.util.LazyLoader" ).

[importlib.util.cache_from_source()](https://docs.python.org/3.6/library/imp ortlib.html#importlib.util.cache_from_source "importlib.util.cache_from_source" ), [importlib.util.source_from_cache()](h ttps://docs.python.org/3.6/library/importlib.html#importlib.util.source_from_c ache "importlib.util.source_from_cache" ), and [importlib.util.spec_from_file _location()](https://docs.python.org/3.6/library/importlib.html#importlib.uti l.spec_from_file_location "importlib.util.spec_from_file_location" ) now accept a [path-like object](https://docs.python.org/3.6/glossary.html#term- 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](https://docs.python.org/3.6/library/exceptions.html#Reso urceWarning "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](https://docs.python.org/3.6/library/pickle.html #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()](https://docs.python.org/3.6/library/readline.html #readline.set_auto_history "readline.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](https://docs.python.org/3.6/library/sqlite3.html# sqlite3.Cursor.lastrowid "sqlite3.Cursor.lastrowid" ) now supports the REPLACE statement. (Contributed by Alex LordThorsen in issue 16864.)

socket

The [ioctl()](https://docs.python.org/3.6/library/socket.html#socket.socket. ioctl "socket.socket.ioctl" ) function now supports the [SIO_LOOPBACK_FAST_PA TH](https://docs.python.org/3.6/library/socket.html#socket.SIO_LOOPBACK_FAST_ PATH "socket.SIO_LOOPBACK_FAST_PATH" ) control code. (Contributed by Daniel Stokes in issue 26536.)

The [getsockopt()](https://docs.python.org/3.6/library/socket.html#socket.so cket.getsockopt "socket.socket.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()](https://docs.python.org/3.6/library/socket.h tml#socket.socket.sendmsg_afalg "socket.socket.sendmsg_afalg" ) were added. (Contributed by Christian Heimes in issue 27744 with support from Victor Stinner.)

socketserver

Servers based on the [socketserver](https://docs.python.org/3.6/library/socketserver.html#module- socketserver "socketserver: A framework for network servers." ) module, including those defined in [http.server](https://docs.python.org/3.6/library/http.server.html#module- http.server "http.server: HTTP server and request handlers." ), [xmlrpc.server](https://docs.python.org/3.6/library/xmlrpc.server.html #module-xmlrpc.server "xmlrpc.server: Basic XML-RPC server implementations." ) and [wsgiref.simple_server](https://docs.python.org/3.6/library/wsgiref.html #module-wsgiref.simple_server "wsgiref.simple_server: A simple WSGI HTTP server." ), now support the context manager protocol. (Contributed by Aviv Palivoda in issue 26404.)

The wfile attribute of [StreamRequestHandler](https://docs.python.org/3.6/ library/socketserver.html#socketserver.StreamRequestHandler "socketserver.StreamRequestHandler" ) classes now implements the io.Buffered IOBase writable interface. In particular, calling [write()](h ttps://docs.python.org/3.6/library/io.html#io.BufferedIOBase.write "io.BufferedIOBase.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](https://docs.python.org/3.6/library/subprocess.html#subpr ocess.Popen "subprocess.Popen" ) destructor now emits a [ResourceWarning](ht tps://docs.python.org/3.6/library/exceptions.html#ResourceWarning "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](https://docs.python.org/3.6/library/subprocess.html#s ubprocess.Popen "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](https://docs.python.org/3.6/library/typing.html# typing.ContextManager "typing.ContextManager" ) class has been added for representing [contextlib.AbstractContextManager](https://docs.python.org/3.6 /library/contextlib.html#contextlib.AbstractContextManager "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](https://docs.python.org/3.6/library/unittest.mock.html#unittest.m ock.Mock "unittest.mock.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 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](https://docs.python.org/3.6/library/urllib.robotparser.htm l#urllib.robotparser.RobotFileParser "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_explic it()](https://docs.python.org/3.6/library/warnings.html#warnings.warn_explici t "warnings.warn_explicit" ) function: the destroyed object which emitted a [ ResourceWarning](https://docs.python.org/3.6/library/exceptions.html#Resource Warning "ResourceWarning" ). A source attribute has also been added to warnings.WarningMessage (contributed by Victor Stinner in issue 26568 and issue 26567).

When a [ResourceWarning](https://docs.python.org/3.6/library/exceptions.html #ResourceWarning "ResourceWarning" ) warning is logged, the [tracemalloc](https://docs.python.org/3.6/library/tracemalloc.html#module- tracemalloc "tracemalloc: Trace memory allocations." ) 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](https://docs.python.org/3.6/library/tracemalloc.html#module- tracemalloc "tracemalloc: Trace memory allocations." ) 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](https://docs.python.org/3.6/library/winsoun d.html#winsound.MessageBeep "winsound.MessageBeep" ), and [PlaySound](https: //docs.python.org/3.6/library/winsound.html#winsound.PlaySound "winsound.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()](https://docs.python.org/3.6/library/zipfile.html #zipfile.ZipInfo.from_file "zipfile.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()](https://docs.python.org/3.6/library/zipfile.html#zipfil e.ZipFile.open "zipfile.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()](https://docs.python.org/3.6/library/fileinput.html#fileinpu t.hook_encoded "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 and replace (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 and surrogateescape (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() and bytearray.fromhex(): they are now between 2x and 3.5x faster. (Contributed by Victor Stinner in issue 25401).

• Optimize bytes.replace(b'', b'.') and bytearray.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 of malloc() function of the C library. The pymalloc allocator is optimized for objects smaller or equal to 512 bytes with a short lifetime, and use malloc() for larger memory blocks. (Contributed by Victor Stinner in issue 26249).

• pickle.load() and pickle.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() and iglob() functions in the glob module; they are now about 3-6 times faster. (Contributed by Serhiy Storchaka in issue 25596).

• Optimized globbing in pathlib by using os.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() and importlib.machinery.SourcelessFileLoader.load_module() are now deprecated. They were the only remaining implementations of importlib.abc.Loader.load_module() in importlib that had not been deprecated in previous versions of Python in favour of importlib.abc.Loader.exec_module().
• The tkinter.tix module is now deprecated. tkinter users should use tkinter.ttk instead.

Deprecated functions and types of the C API

• None yet.

Deprecated features

• The pyvenv script has been deprecated in favour of python3 -m venv. This prevents confusion as to what Python interpreter pyvenv 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 an ImportWarning. (Contributed by Rose Ames in issue 25791.)
• Unlike to other [dbm](https://docs.python.org/3.6/library/dbm.html#module-dbm "dbm: Interfaces to various Unix "database" formats." ) implementations, the dbm.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 Python re 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 and check_hostname in ftplib, http.client, imaplib, poplib, and smtplib have been deprecated in favor of context. (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 a DeprecationWarning, and will trigger a RuntimeError 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 and traceback.usage, traceback.modname, traceback.fullmodname, traceback.find_lines_from_code, traceback.find_lines, traceback.find_strings, traceback.find_executable_lines methods were removed from the traceback module. They were undocumented methods deprecated since Python 3.2 and equivalent functionality is available from private methods.
• The tk_menuBar() and tk_bindForTraversal() dummy methods in tkinter widget classes were removed (corresponding Tk commands were obsolete since Tk 4.0).
• The open() method of the zipfile.ZipFile class no longer supports the 'U' mode (was deprecated since Python 3.4). Use io.TextIOWrapper for reading compressed text files in universal newlines mode.
• The undocumented IN, CDROM, DLFCN, TYPES, CDIO, and STROPTS modules have been removed. They had been available in the platform specific Lib/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 or SHOW_TRACK_COUNT macros is now off by default. It can be re-enabled using the -X showalloccount option. It now outputs to stderr instead of stdout. (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 sets TypeError when its msg argument is not set. Previously only NULL 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 using frame.f_lineno, PyFrame_GetLineNumber() or PyCode_Addr2Line() are not affected. Functions decoding directly co_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. See Objects/lnotab_notes.txt for the co_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 of 1 or 0 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 for 1 or 0. See issue 25768.

• Reading the port attribute of urllib.parse.urlsplit() and urlparse() results now raises ValueError for out-of-range values, rather than returning None. See issue 20059.

• The imp module now raises a DeprecationWarning instead of PendingDeprecationWarning.

• 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 and wave. This means they will export new symbols when import * is used. See issue 23883.

• When performing a relative import, if __package__ does not compare equal to __spec__.parent then ImportWarning 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 in http.server, xmlrpc.server and wsgiref.simple_server, now only catch exceptions derived from Exception. Therefore if a request handler raises an exception like SystemExit or KeyboardInterrupt, 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 a PermissionError instead of KeyError 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 and smtpd.SMTPServer constructors is now False by default. This means that the argument passed to process_message() is now a bytes object by default, and process_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() and loads() functions and JSONEncoder and JSONDecoder class constructors in the json 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 to object.__init_subclass__(). This means that type.__new__() and type.__init__() both now accept arbitrary keyword arguments, but object.__init_subclass__() (which is called from type.__new__()) will reject them by default. Custom metaclasses accepting additional keyword arguments will need to adjust their calls to type.__new__() (whether direct or via super) accordingly.

• In distutils.command.sdist.sdist, the default_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 a setup.cfg file containing the following:

    formats=zip
    

This behavior has also been backported to earlier Python versions by Setuptools 26.0.0.

• In the urllib.request module and the http.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 system malloc(). Applications calling PyMem_Malloc() without holding the GIL can now crash. Set the PYTHONMALLOC environment variable to debug 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.