Python 3.6 有什么新变化A
************************

作者:
   Elvis Pranskevichus <elvis@magic.io>, Yury Selivanov
   <yury@magic.io>

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.

参见: **PEP 494** - Python 3.6发布计划


摘要 - 发布重点
===============

新的语法特性：

* PEP 498, 格式化的字符串文字

* PEP 515, 数字文字中的下划线。

* PEP 526 , 变量注释的语法。

* PEP 525, 异步生成器。

* PEP 530: 异步推导。

新的库模块：

* "secrets": PEP 506 -- Secrets模块被加入Python标准库。

CPython 实现的改进：

* 根据 Raymond Hettinger 的提议  已将 dict 类型重新实现为使用 更紧凑的
  表示形式 并类似于 PyPy dict implementation。 这使得字典所使用的内存
  相对于 Python 3.5 版减少了 20% 到 25%。

* 类创建的定制过程通过 新协议 得到了简化。

* 类属性的定义顺序 现在会被保留。

* 现在 "**kwargs" 中的元素会与传给函数的关键字参数 保持对应顺序。

* 添加了 DTrace 和 SystemTap 探测支持

* 新的 PYTHONMALLOC 环境变量可被用来调试解释器的内存分配和访问错误。

标准库中的重大改进：

* "asyncio" 模块获得了许多新特性，显著的可用性和性能提升，以及大量的问
  题修正。 从 Python 3.6 开始 "asyncio" 模块不再处于待定状态，它已被视
  为稳定 API。

* 实现了新的 文件系统路径协议 以支持 *路径类对象*。 所有操作路径的标准
  库函数已被更新为使用新的协议。

* "datetime" 模块已获得对 本地时间消歧义 的支持。

* "typing" 模块获得了大量的 改进。

* "tracemalloc" 模块已被大幅重写，现在将被用于为 "ResourceWarning" 提
  供更好的输出，并为内存分配错误提供更好的诊断。 请参阅 PYTHONMALLOC
  一节 来了解详情。

安全改进：

* 添加了 "secrets" 模块以简化适用于密码管理的高加密强度伪随机数的生成
  ，例如账户验证、安全凭据等场景。

* 在 Linux 上，现在 "os.urandom()" 会阻塞直到系统的 urandom 熵池被初始
  化以提升安全性。 其理由参见 **PEP 524**。

* "hashlib" 和 "ssl" 模块现在支持 OpenSSL 1.1.0。

* "ssl" 模块的默认设置和特性集已得到改进。

* "hashlib" 模块获得了对 BLAKE2, SHA-3 和 SHAKE 哈希算法以及
  "scrypt()" 密钥派生函数的支持。

Windows改进：

* PEP 528 和 PEP 529, 将Windows文件系统和控制台的编码更改为UTF-8

* 在交互式地使用 "py.exe" 启动器时，当用户未（通过命令行参数或配置文件
  ）指定版本时不再优先选择 Python 2 而是选择 Python 3。 对声明行的处理
  则保持不变 —— 在这种情况下 "python" 还是指 Python 2。

* "python.exe" 和 "pythonw.exe" 已被标记为支持长路径，这意味着不再有
  260 个字符的路径长度限制。 详情参见 移除 MAX_PATH 限制。

* 可以添加一个 "._pth" 文件来强制使用隔离模式和完整指定所有搜索路径来
  避免注册表和环境查找。 更多信息请参阅 相关文档。

* 现在 "python36.zip" 文件可以作为推断 "PYTHONHOME" 的标志。 更多信息
  请参阅 相关文档。


新的特性
========


PEP 498: 格式化的字符串文字
---------------------------

**PEP 498** 引入了一种新型的字符串字面值: *f-字符串*，或称 格式化字符
串字面值。

格式化字符串字面值带有 "'f'" 前缀并且类似于 "str.format()" 所接受的格
式字符串。 其中包含由花括号包围的替换字段。 替换字段属于表达式，它们会
在运行时被求值，然后使用 "format()" 协议进行格式化:

   >>> name = "Fred"
   >>> f"He said his name is {name}."
   'He said his name is Fred.'
   >>> width = 10
   >>> precision = 4
   >>> value = decimal.Decimal("12.34567")
   >>> f"result: {value:{width}.{precision}}"  # nested fields
   'result:      12.35'

参见:

  **PEP 498** -- 文字字符串插值。
     PEP 由 Eric V. Smith 撰写并实现

  Feature documentation.


PEP 526: 变量注释的语法
-----------------------

**PEP 484** 引入了函数形参类型标注即类型提示的标准。 这个 PEP 为
Python 添加了标注变量类型的语法，包括类变量和实例变量:

   primes: List[int] = []

   captain: str  # Note: no initial value!

   class Starship:
       stats: Dict[str, int] = {}

与函数标注一样，Python 解释器不会为变量标注附加任何特殊含义，仅会将其
保存在类或模块的 "__annotations__" 属性中。

与静态类型语法的变量声明不同，标注语法的目的是通过抽象语法树和
"__annotations__" 属性提供一个简单方式来为第三方工具和库指定结构化类型
元数据。

参见:

  **PEP 526** -- 变量注释的语法。
     PEP 由 Ryan Gonzalez, Philip House, Ivan Levkivskyi, Lisa Roach,
     和 Guido van Rossum 撰写，由 Ivan Levkivskyi 实现。

  使用或将要使用此新语法的工具有: mypy, pytype, PyCharm 等等。


PEP 515: 数字文字中的下划线。
-----------------------------

**PEP 515** 增加了在数字字面值中使用下划线的能力以改善可读性。 例如:

   >>> 1_000_000_000_000_000
   1000000000000000
   >>> 0x_FF_FF_FF_FF
   4294967295

单个下划线允许用在数码之间和任何数制指示符之后。 一行内不允许有开头、
末尾或多个下划线。

字符串格式化 微语言现在也支持以 "'_'" 选项来表示用下划线作为浮点表示类
型和整数表示类型 "'d'" 的千位分隔符。 对于整数表示类型 "'b'", "'o'",
"'x'" 和 "'X'"，将每隔 4 个数码插入一个下划线:

   >>> '{:_}'.format(1000000)
   '1_000_000'
   >>> '{:_x}'.format(0xFFFFFFFF)
   'ffff_ffff'

参见:

  **PEP 515** -- 数字文字中的下划线。
     PEP 由 Georg Brandl 和 Serhiy Storchaka 撰写


PEP 525: 异步生成器
-------------------

**PEP 492** 将对原生协程和 "async" / "await" 语法的支持引入到 Python
3.5 中。 但 Python 3.5 实现的一个明显限制是不可能在同一函数体中同时使
用 "await" 和 "yield"。 在 Python 3.6 中此限制已被解除，这样就就能够定
义 *异步生成器*:

   async def ticker(delay, to):
       """Yield numbers from 0 to *to* every *delay* seconds."""
       for i in range(to):
           yield i
           await asyncio.sleep(delay)

这个新语法允许更快速且更精简的代码。

参见:

  **PEP 525** -- 异步生成器
     PEP 由 Yury Selivanov 撰写并实现


PEP 530: 异步推导
-----------------

**PEP 530** 添加了对在列表、集合与字典推导式和生成器表达式中使用
"async for" 的支持:

   result = [i async for i in aiter() if i % 2]

此外，"await" 表达式也在所有种类的推导式中得到支持:

   result = [await fun() for fun in funcs if await condition()]

参见:

  **PEP 530** -- 异步推导
     PEP 由 Yury Selivanov 撰写并实现


PEP 487: 自定义类创建
---------------------

现在可以在不使用元类的情况下自定义子类的创建。 当一个新的子类被创建时
将在基类上调用新的 "__init_subclass__" 类方法:

   class PluginBase:
       subclasses = []

       def __init_subclass__(cls, **kwargs):
           super().__init_subclass__(**kwargs)
           cls.subclasses.append(cls)

   class Plugin1(PluginBase):
       pass

   class Plugin2(PluginBase):
       pass

为了让来自 "__init_subclass__()" 实现的零参数 "super()" 调用能正确工作
，自定义元类必须保证新的 "__classcell__" 命名空间入口被传播到
"type.__new__" (如 创建类对象 中所描述)。

参见:

  **PEP 487** -- 自定义类创建
     PEP 由 Martin Teichmann 撰写并实现。

  特性文档


PEP 487: 描述器协议的增强
-------------------------

**PEP 487** 扩展了描述器协议以包括新的可选方法 "__set_name__()"。 当创
建一个新类时，这个新方法将在定义中包括的所有描述器上被调用，为它们提供
对所定义类的引用以及在类命名中间中给予描述器的名称。 换句话说，描述器
的实例现在能知道描述器在所有者类中的属性名称:

   class IntField:
       def __get__(self, instance, owner):
           return instance.__dict__[self.name]

       def __set__(self, instance, value):
           if not isinstance(value, int):
               raise ValueError(f'expecting integer in {self.name}')
           instance.__dict__[self.name] = value

       # this is the new initializer:
       def __set_name__(self, owner, name):
           self.name = name

   class Model:
       int_field = IntField()

参见:

  **PEP 487** -- 自定义类创建
     PEP 由 Martin Teichmann 撰写并实现。

  特性文档


PEP 519: 添加文件系统路径协议
-----------------------------

File system paths have historically been represented as "str" or
"bytes" objects. This has led to people who write code which operate
on file system paths to assume that such objects are only one of those
two types (an "int" representing a file descriptor does not count as
that is not a file path). Unfortunately that assumption prevents
alternative object representations of file system paths like "pathlib"
from working with pre-existing code, including Python's standard
library.

To fix this situation, a new interface represented by "os.PathLike"
has been defined. By implementing the "__fspath__()" method, an object
signals that it represents a path. An object can then provide a low-
level representation of a file system path as a "str" or "bytes"
object. This means an object is considered *path-like* if it
implements "os.PathLike" or is a "str" or "bytes" object which
represents a file system path. Code can use "os.fspath()",
"os.fsdecode()", or "os.fsencode()" to explicitly get a "str" and/or
"bytes" representation of a path-like object.

The built-in "open()" function has been updated to accept
"os.PathLike" objects, as have all relevant functions in the "os" and
"os.path" modules, 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".

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).

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'

（由 Brett Cannon, Ethan Furman, Dusty Phillips 和 Jelle Zijlstra 实现
。）

参见:

  **PEP 519** -- 添加文件系统路径协议
     PEP 由 Brett Cannon 和 Koos Zevenhoven 撰写。


PEP 495: 消除本地时间的歧义
---------------------------

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.

**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:

   >>> u0 = datetime(2016, 11, 6, 4, tzinfo=timezone.utc)
   >>> for i in range(4):
   ...     u = u0 + i*HOUR
   ...     t = u.astimezone(Eastern)
   ...     print(u.time(), 'UTC =', t.time(), t.tzname(), t.fold)
   ...
   04:00:00 UTC = 00:00:00 EDT 0
   05:00:00 UTC = 01:00:00 EDT 0
   06:00:00 UTC = 01:00:00 EST 1
   07:00:00 UTC = 02:00:00 EST 0

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.

参见:

  **PEP 495** -- 消除本地时间的歧义
     PEP 由 Alexander Belopolsky 和 Tim Peters 撰写，由 Alexander
     Belopolsky 实现。


PEP 529: 将Windows文件系统编码更改为UTF-8
-----------------------------------------

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

Prior to Python 3.6, data loss could result when using bytes paths on
Windows. With this change, using bytes to represent paths is now
supported on Windows, provided those bytes are encoded with the
encoding returned by "sys.getfilesystemencoding()", which now defaults
to "'utf-8'".

Applications that do not use str to represent paths should use
"os.fsencode()" and "os.fsdecode()" to ensure their bytes are
correctly encoded. To revert to the previous behaviour, set
"PYTHONLEGACYWINDOWSFSENCODING" or call
"sys._enablelegacywindowsfsencoding()".

有关详细信息和可能需要的代码修改的讨论，请参见 **PEP 529** 。


PEP 528: 将Windows控制台编码更改为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 "PYTHONLEGACYWINDOWSSTDIO".

参见:

  **PEP 528** -- 将Windows控制台编码更改为UTF-8
     PEP 由 Steve Dower 撰写并实现。


PEP 520: 保留类属性定义顺序
---------------------------

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.

参见:

  **PEP 520** -- 保留类属性定义顺序
     PEP 由 Eric Snow 撰写并实现


PEP 468: 保留关键字参数顺序
---------------------------

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

参见:

  **PEP 468** -- 保留关键字参数顺序
     PEP 由 Eric Snow 撰写并实现


新的 dict 实现
--------------

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.

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 bpo-27350. Idea originally suggested by
Raymond Hettinger.)


PEP 523: 向CPython 添加框架评估API
----------------------------------

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.

参见:

  **PEP 523** -- 向CPython 添加框架评估API
     PEP 由 Brett Cannon 和 Dino Viehland 撰写。


PYTHONMALLOC 环境变量
---------------------

The new "PYTHONMALLOC" environment variable allows setting the Python
memory allocators and installing 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:

* 新分配的内存中填充字节 "0xCB"

* 释放的内存中填充了字节 "0xDB"

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

* 在缓冲区开始之前检测写操作（缓冲区下溢）

* 在缓冲区结束后检测写操作（缓冲区溢出）

* 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.

检查是否保留了 GIL 也是Python 3.6 的新特性。

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

It is now also possible to force the usage of the "malloc()" allocator
of the C library for all Python memory allocations using
"PYTHONMALLOC=malloc". This is helpful when using external memory
debuggers like Valgrind on a Python compiled in release mode.

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

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

   Debug memory block at address p=0x7fbcd41666f8: API 'o'
       4 bytes originally requested
       The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
       The 8 pad bytes at tail=0x7fbcd41666fc are not all FORBIDDENBYTE (0xfb):
           at tail+0: 0x02 *** OUCH
           at tail+1: 0xfb
           at tail+2: 0xfb
           at tail+3: 0xfb
           at tail+4: 0xfb
           at tail+5: 0xfb
           at tail+6: 0xfb
           at tail+7: 0xfb
       The block was made by call #1233329 to debug malloc/realloc.
       Data at p: 1a 2b 30 00

   Memory block allocated at (most recent call first):
     File "test/test_bytes.py", line 323
     File "unittest/case.py", line 600
     File "unittest/case.py", line 648
     File "unittest/suite.py", line 122
     File "unittest/suite.py", line 84

   Fatal Python error: bad trailing pad byte

   Current thread 0x00007fbcdbd32700 (most recent call first):
     File "test/test_bytes.py", line 323 in test_hex
     File "unittest/case.py", line 600 in run
     File "unittest/case.py", line 648 in __call__
     File "unittest/suite.py", line 122 in run
     File "unittest/suite.py", line 84 in __call__
     File "unittest/suite.py", line 122 in run
     File "unittest/suite.py", line 84 in __call__
     ...

（由 Victor Stinner 在 bpo-26516 和 bpo-26564 中贡献。）


DTrace 和 SystemTap 探测支持
----------------------------

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

* 函数调用/返回

* 垃圾收集开始/完成

* 执行的代码行。

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.

更多信息，请参见 使用 DTrace 和 SystemTap 检测CPython 。

当前的实现已在 Linux 和 macOS 上进行了测试。将来可能会添加其他标记。

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


其他语言特性修改
================

对Python 语言核心进行的小改动：

* 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".

* 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.)

* Long sequences of repeated traceback lines are now abbreviated as
  ""[Previous line repeated {count} more times]"" (see 回溯 for an
  example). (Contributed by Emanuel Barry in bpo-26823.)

* 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.)

* 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.)


新增模块
========


secrets
-------

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.

警告:

  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.

参见:

  **PEP 506** -- Secrets模块被加入Python标准库
     PEP 由 Steven D'Aprano 撰写并实现。


改进的模块
==========


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.

（由 Serhiy Storchaka 在 bpo-26492 中贡献。）


ast
---

The new "ast.Constant" AST node has been added.  It can be used by
external AST optimizers for the purposes of constant folding.

（由 Victor Stinner 在 bpo-26146 中贡献。）


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.)


datetime
--------

The "datetime" and "time" classes have the new "fold" attribute used
to disambiguate local time when necessary.  Many functions in the
"datetime" have been updated to support local time disambiguation. See
Local Time Disambiguation section for more information. (Contributed
by Alexander Belopolsky in bpo-24773.)

The "datetime.strftime()" and "date.strftime()" methods now support
ISO 8601 date directives "%G", "%u" and "%V". (Contributed by Ashley
Anderson in bpo-12006.)

The "datetime.isoformat()" function now accepts an optional *timespec*
argument that specifies the number of additional components of the
time value to include. (Contributed by Alessandro Cucci and Alexander
Belopolsky in bpo-19475.)

The "datetime.combine()" now accepts an optional *tzinfo* argument.
(Contributed by Alexander Belopolsky in bpo-27661.)


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)

（由 Stefan Krah 和 Mark Dickinson  在 bpo-25928 中贡献。）


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 与 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.

在 3.6.2 中新增:

多个对自动补全的修正。 （由 Louie Lu 在 bpo-15786 中贡献。）

在 3.6.3 中新增:

Module Browser (在 File 菜单中，之前称为 Class Browser) 现在会在最高层
级函数和类之外显示嵌套的函数和类。 （由 Guilherme Polo, Cheryl Sabella
和 Terry Jan Reedy 在 bpo-1612262 中贡献。）

之前以扩展形式实现的 IDLE 特性已作为正常特性重新实现。 它们的设置已从
Extensions 选项卡移至其他对话框选项卡。 （由 Charles Wohlganger 和
Terry Jan Reedy 在 bpo-27099 中实现。）

Settings 对话框 (Options 中的 Configure IDLE) 已经被部分重写以改进外观
和功能。 （由 Cheryl Sabella 和 Terry Jan Reedy 在多个问题项中贡献。）

在 3.6.4 中新增:

字体样本现在包括一组非拉丁字符以便用户能更好地查看所选特定字体的效果。
（由 Terry Jan Reedy 在 bpo-13802 中贡献。） 样本可以被修改以包括其他
字符。 （由 Serhiy Storchaka 在 bpo-31860 中贡献。）

在 3.6.6 中新增:

编辑器代码上下文选项已经过修改。 Box 会显示所有上下文行直到最大行数。
点击一个上下文行会使编辑器跳转到该行。 自定义主题的上下文颜色已添加到
Settings 对话框的 Highlights 选项卡。 （由 Cheryl Sabella 和 Terry Jan
Reedy 在 bpo-33642, bpo-33768 和 bpo-33679 中贡献。）

在 Windows 上，会有新的 API 调用将 tk 对 DPI 的调整告知 Windows。 在
Windows 8.1+ 或 10 上，如果 Python 二进制码的 DPI 兼容属性未改变，并且
监视器分辨率大于 96 DPI，这应该会令文本和线条更清晰。 否则的话它应该不
造成影响。 （由 Terry Jan Reedy 在 bpo-33656 中贡献。）

在 3.6.7 中新增:

超过 N 行（默认值为 50）的输出将被折叠为一个按钮。 N 可以在 Settings
对话框的 General 页的 PyShell 部分中进行修改。 数量较少但是超长的行可
以通过在输出上右击来折叠。 被折叠的输出可通过双击按钮来展开，或是通过
右击按钮来放入剪贴板或是单独的窗口。 （由 Tal Einat 在 bpo-1529353 中
贡献。）


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.)


os
--

See the summary of PEP 519 for details on how the "os" and "os.path"
modules now support *path-like objects*.

"scandir()" now supports "bytes" paths on Windows.

A new "close()" method allows explicitly closing a "scandir()"
iterator.  The "scandir()" iterator now supports the *context manager*
protocol.  If a "scandir()" iterator is neither exhausted nor
explicitly closed a "ResourceWarning" will be emitted in its
destructor. (Contributed by Serhiy Storchaka in bpo-25994.)

在 Linux 上，现在 "os.urandom()" 会阻塞直到系统的 urandom 熵池被初始化
以提升安全性。 其理由参见 **PEP 524**。

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**)


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.)


pickletools
-----------

"pickletools.dis()" now outputs the implicit memo index for the
"MEMOIZE" opcode. (Contributed by Serhiy Storchaka in bpo-25382.)


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).


回溯
----

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

（由  Emanuel Barry在 bpo-26823 中贡献。）


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).

（由 Victor Stinner 在 bpo-26588 中贡献。）


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.)


zlib
----

The "compress()" and "decompress()" functions now accept keyword
arguments. (Contributed by Aviv Palivoda in bpo-26243 and Xiang Zhang
in bpo-16764 respectively.)


性能优化
========

* The Python interpreter now uses a 16-bit wordcode instead of
  bytecode which made a number of opcode optimizations possible.
  (Contributed by Demur Rumed with input and reviews from Serhiy
  Storchaka and Victor Stinner in bpo-26647 and bpo-28050.)

* The "asyncio.Future" class now has an optimized C implementation.
  (Contributed by Yury Selivanov and INADA Naoki in bpo-26081.)

* The "asyncio.Task" class now has an optimized C implementation.
  (Contributed by Yury Selivanov in bpo-28544.)

* Various implementation improvements in the "typing" module (such as
  caching of generic types) allow up to 30 times performance
  improvements and reduced memory footprint.

* The ASCII decoder is now up to 60 times as fast for error handlers
  "surrogateescape", "ignore" and "replace" (Contributed by Victor
  Stinner in bpo-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 bpo-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 bpo-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 bpo-25301).

* "bytes % args" is now up to 2 times faster. (Contributed by Victor
  Stinner in bpo-25349).

* "bytearray % args" is now between 2.5 and 5 times faster.
  (Contributed by Victor Stinner in bpo-25399).

* Optimize "bytes.fromhex()" and "bytearray.fromhex()": they are now
  between 2x and 3.5x faster. (Contributed by Victor Stinner in
  bpo-25401).

* Optimize "bytes.replace(b'', b'.')" and "bytearray.replace(b'',
  b'.')": up to 80% faster. (Contributed by Josh Snider in bpo-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 bpo-26249).

* "pickle.load()" and "pickle.loads()" are now up to 10% faster when
  deserializing many small objects (Contributed by Victor Stinner in
  bpo-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
  bpo-27574).

* Optimized "glob()" and "iglob()" functions in the "glob" module;
  they are now about 3--6 times faster. (Contributed by Serhiy
  Storchaka in bpo-25596).

* Optimized globbing in "pathlib" by using "os.scandir()"; it is now
  about 1.5--4 times faster. (Contributed by Serhiy Storchaka in
  bpo-26032).

* "xml.etree.ElementTree" parsing, iteration and deepcopy performance
  has been significantly improved. (Contributed by Serhiy Storchaka in
  bpo-25638, bpo-25873, and bpo-25869.)

* Creation of "fractions.Fraction" instances from floats and decimals
  is now 2 to 3 times faster. (Contributed by Serhiy Storchaka in
  bpo-25971.)


构建和 C API 的改变
===================

* Python now requires some C99 support in the toolchain to build. Most
  notably, Python now uses standard integer types and macros in place
  of custom macros like "PY_LONG_LONG". For more information, see
  **PEP 7** and bpo-17884.

* Cross-compiling CPython with the Android NDK and the Android API
  level set to 21 (Android 5.0 Lollipop) 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 bpo-26865.

* The "--enable-optimizations" configure flag has been added. Turning
  it on will activate expensive optimizations like PGO. (Original
  patch by Alecsandru Patrascu of Intel in bpo-26359.)

* The *GIL* must now be held when allocator functions of
  "PYMEM_DOMAIN_OBJ" (ex: "PyObject_Malloc()") and "PYMEM_DOMAIN_MEM"
  (ex: "PyMem_Malloc()") domains are called.

* New "Py_FinalizeEx()" API which indicates if flushing buffered data
  failed. (Contributed by Martin Panter in bpo-5319.)

* "PyArg_ParseTupleAndKeywords()" now supports positional-only
  parameters.  Positional-only parameters are defined by empty names.
  (Contributed by Serhiy Storchaka in bpo-26282).

* "PyTraceback_Print" method now abbreviates long sequences of
  repeated lines as ""[Previous line repeated {count} more times]"".
  (Contributed by Emanuel Barry in bpo-26823.)

* The new "PyErr_SetImportErrorSubclass()" function allows for
  specifying a subclass of "ImportError" to raise. (Contributed by
  Eric Snow in bpo-15767.)

* The new "PyErr_ResourceWarning()" function can be used to generate a
  "ResourceWarning" providing the source of the resource allocation.
  (Contributed by Victor Stinner in bpo-26567.)

* The new "PyOS_FSPath()" function returns the file system
  representation of a *path-like object*. (Contributed by Brett Cannon
  in bpo-27186.)

* The "PyUnicode_FSConverter()" and "PyUnicode_FSDecoder()" functions
  will now accept *path-like objects*.


其他改进
========

* When "--version" (short form: "-V") is supplied twice, Python prints
  "sys.version" for detailed information.

     $ ./python -VV
     Python 3.6.0b4+ (3.6:223967b49e49+, Nov 21 2016, 20:55:04)
     [GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]


弃用
====


新关键字
--------

"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.  Starting in Python
3.6, the use of "async" or "await" as names will generate a
"DeprecationWarning".


已弃用的 Python 行为
--------------------

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.

The "__aiter__()" method is now expected to return an asynchronous
iterator directly instead of returning an awaitable as previously.
Doing the former will trigger a "DeprecationWarning".  Backward
compatibility will be removed in Python 3.7. (Contributed by Yury
Selivanov in bpo-27243.)

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 bpo-27364.)

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 bpo-25791.)


已弃用的 Python 模块、函数和方法
--------------------------------


asynchat
~~~~~~~~

The "asynchat" has been deprecated in favor of "asyncio". (Contributed
by Mariatta in bpo-25002.)


asyncore
~~~~~~~~

The "asyncore" has been deprecated in favor of "asyncio". (Contributed
by Mariatta in bpo-25002.)


dbm
~~~

Unlike other "dbm" implementations, the "dbm.dumb" module creates
databases with the "'rw'" mode and allows modifying the database
opened with the "'r'" mode.  This behavior is now deprecated and will
be removed in 3.8. (Contributed by Serhiy Storchaka in bpo-21708.)


distutils
~~~~~~~~~

The undocumented "extra_path" argument to the "Distribution"
constructor is now considered deprecated and will raise a warning if
set.   Support for this parameter will be removed in a future Python
release.  See bpo-27919 for details.


grp
~~~

The support of non-integer arguments in "getgrgid()" has been
deprecated. (Contributed by Serhiy Storchaka in bpo-26129.)


importlib
~~~~~~~~~

The "importlib.machinery.SourceFileLoader.load_module()" and
"importlib.machinery.SourcelessFileLoader.load_module()" methods 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 "importlib.machinery.WindowsRegistryFinder" class is now
deprecated. As of 3.6.0, it is still added to "sys.meta_path" by
default (on Windows), but this may change in future releases.


os
~~

Undocumented support of general *bytes-like objects* as paths in "os"
functions, "compile()" and similar functions is now deprecated.
(Contributed by Serhiy Storchaka in bpo-25791 and bpo-26754.)


re
~~

Support for inline flags "(?letters)" in the middle of the regular
expression has been deprecated and will be removed in a future Python
version.  Flags at the start of a regular expression are still
allowed. (Contributed by Serhiy Storchaka in bpo-22493.)


ssl
~~~

OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported.
In the future the "ssl" module will require at least OpenSSL 1.0.2 or
1.1.0.

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 bpo-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 bpo-28022 and
bpo-26470.)


tkinter
~~~~~~~

The "tkinter.tix" module is now deprecated.  "tkinter" users should
use "tkinter.ttk" instead.


venv
~~~~

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 bpo-25154.)


xml
---

* As mitigation against DTD and external entity retrieval, the
  "xml.dom.minidom" and mod:*xml.sax* modules no longer process
  external entities by default. (Contributed by Christian Heimes in
  bpo-17239.)


已弃用的 C API 函数和类型
-------------------------

Undocumented functions "PyUnicode_AsEncodedObject()",
"PyUnicode_AsDecodedObject()", "PyUnicode_AsEncodedUnicode()" and
"PyUnicode_AsDecodedUnicode()" are deprecated now. Use the generic
codec based API instead.


弃用的构建选项
--------------

The "--with-system-ffi" configure flag is now on by default on non-
macOS 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. macOS is unaffected by this change.  Note that many OS
distributors already use the "--with-system-ffi" flag when building
their system Python.


移除
====


API 与特性的移除
----------------

* Unknown escapes consisting of "'\'" and an ASCII letter in regular
  expressions will now cause an error.  In replacement templates for
  "re.sub()" they are still allowed, but deprecated. The "re.LOCALE"
  flag can now only be used with binary patterns.

* "inspect.getmoduleinfo()" was removed (was deprecated since CPython
  3.3). "inspect.getmodulename()" should be used for obtaining the
  module name for a given path. (Contributed by Yury Selivanov in
  bpo-13248.)

* "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.

* The deprecated "asynchat.fifo" class has been removed.


移植到Python 3.6
================

本节列出了先前描述的更改以及可能需要更改代码的其他错误修正.


 'python' 命令行为的变化
------------------------

* 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 bpo-23034.)


更改的Python API
----------------

* "open()" will no longer allow combining the "'U'" mode flag with
  "'+'". (Contributed by Jeff Balogh and John O'Connor in bpo-2091.)

* "sqlite3" no longer implicitly commits 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 a negative line number delta. By default, Python does not
  emit bytecode with a negative line number delta. Functions using
  "frame.f_lineno", "PyFrame_GetLineNumber()" or "PyCode_Addr2Line()"
  are not affected. Functions directly decoding "co_lnotab" should be
  updated to use a signed 8-bit integer type for the line number
  delta, but this is only required to support applications using a
  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
  bpo-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 bpo-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. (Contributed by Joel Taddei and
  Jacek Kołodziej in bpo-23883.)

* When performing a relative import, if "__package__" does not compare
  equal to "__spec__.parent" then "ImportWarning" is raised.
  (Contributed by Brett Cannon in bpo-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 bpo-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 bpo-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.
  (Contributed by Martin Panter in bpo-26685.)

* The *decode_data* argument for the "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 arguments 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 bpo-18726.)

* "type" 的子类如果未重载 "type.__new__"，将不再能使用一个参数的形式来
  获取对象的类型。

* 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:

     [sdist]
     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. (Contributed by Demian Brecht
  and Rolf Krahl with tweaks from Martin Panter in bpo-12319.)

* The "DictReader" now returns rows of type "OrderedDict".
  (Contributed by Steve Holden in bpo-27842.)

* The "crypt.METHOD_CRYPT" will no longer be added to "crypt.methods"
  if unsupported by the platform. (Contributed by Victor Stinner in
  bpo-25287.)

* The *verbose* and *rename* arguments for "namedtuple()" are now
  keyword-only. (Contributed by Raymond Hettinger in bpo-25628.)

* On Linux, "ctypes.util.find_library()" now looks in
  "LD_LIBRARY_PATH" for shared libraries. (Contributed by Vinay Sajip
  in bpo-9998.)

* The "imaplib.IMAP4" class now handles flags containing the "']'"
  character in messages sent from the server to improve real-world
  compatibility. (Contributed by Lita Cho in bpo-21815.)

* The "mmap.write()" function now returns the number of bytes written
  like other write methods. (Contributed by Jakub Stasiak in
  bpo-26335.)

* The "pkgutil.iter_modules()" and "pkgutil.walk_packages()" functions
  now return "ModuleInfo" named tuples. (Contributed by Ramchandra
  Apte in bpo-17211.)

* "re.sub()" now raises an error for invalid numerical group
  references in replacement templates even if the pattern is not found
  in the string.  The error message for invalid group references now
  includes the group index and the position of the reference.
  (Contributed by SilentGhost, Serhiy Storchaka in bpo-25953.)

* "zipfile.ZipFile" will now raise "NotImplementedError" for
  unrecognized compression values.  Previously a plain "RuntimeError"
  was raised.  Additionally, calling "ZipFile" methods on a closed
  ZipFile or calling the "write()" method on a ZipFile created with
  mode "'r'" will raise a "ValueError". Previously, a "RuntimeError"
  was raised in those scenarios.

* when custom metaclasses are combined with zero-argument "super()" or
  direct references from methods to the implicit "__class__" closure
  variable, the implicit "__classcell__" namespace entry must now be
  passed up to "type.__new__" for initialisation. Failing to do so
  will result in a "DeprecationWarning" in Python 3.6 and a
  "RuntimeError" in Python 3.8.

* With the introduction of "ModuleNotFoundError", import system
  consumers may start expecting import system replacements to raise
  that more specific exception when appropriate, rather than the less-
  specific "ImportError". To provide future compatibility with such
  consumers, implementors of alternative import systems that
  completely replace "__import__()" will need to update their
  implementations to raise the new subclass when a module can't be
  found at all. Implementors of compliant plugins to the default
  import system shouldn't need to make any changes, as the default
  import system will raise the new subclass when appropriate.


C API 中的改变
--------------

* The "PyMem_Malloc()" allocator family now uses the pymalloc
  allocator rather than the 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 bpo-26249.

* "Py_Exit()" (and the main interpreter) now override the exit status
  with 120 if flushing buffered data failed.  See bpo-5319.


CPython 字节码的改变
--------------------

There have been several major changes to the *bytecode* in Python 3.6.

* The Python interpreter now uses a 16-bit wordcode instead of
  bytecode. (Contributed by Demur Rumed with input and reviews from
  Serhiy Storchaka and Victor Stinner in bpo-26647 and bpo-28050.)

* The new "FORMAT_VALUE" and "BUILD_STRING" opcodes as part of the
  formatted string literal implementation. (Contributed by Eric Smith
  in bpo-25483 and Serhiy Storchaka in bpo-27078.)

* The new "BUILD_CONST_KEY_MAP" opcode to optimize the creation of
  dictionaries with constant keys. (Contributed by Serhiy Storchaka in
  bpo-27140.)

* The function call opcodes have been heavily reworked for better
  performance and simpler implementation. The "MAKE_FUNCTION",
  "CALL_FUNCTION", "CALL_FUNCTION_KW" and "BUILD_MAP_UNPACK_WITH_CALL"
  opcodes have been modified, the new "CALL_FUNCTION_EX" and
  "BUILD_TUPLE_UNPACK_WITH_CALL" have been added, and
  "CALL_FUNCTION_VAR", "CALL_FUNCTION_VAR_KW" and "MAKE_CLOSURE"
  opcodes have been removed. (Contributed by Demur Rumed in bpo-27095,
  and Serhiy Storchaka in bpo-27213, bpo-28257.)

* The new "SETUP_ANNOTATIONS" and "STORE_ANNOTATION" opcodes have been
  added to support the new *variable annotation* syntax. (Contributed
  by Ivan Levkivskyi in bpo-27985.)


Python 3.6.2 中的重要变化
=========================


New "make regen-all" build target
---------------------------------

To simplify cross-compilation, and to ensure that CPython can reliably
be compiled without requiring an existing version of Python to already
be available, the autotools-based build system no longer attempts to
implicitly recompile generated files based on file modification times.

Instead, a new "make regen-all" command has been added to force
regeneration of these files when desired (e.g. after an initial
version of Python has already been built based on the pregenerated
versions).

More selective regeneration targets are also defined - see
Makefile.pre.in for details.

（由 Victor Stinner 在 bpo-23404 中贡献。）

3.6.2 新版功能.


Removal of "make touch" build target
------------------------------------

The "make touch" build target previously used to request implicit
regeneration of generated files by updating their modification times
has been removed.

It has been replaced by the new "make regen-all" target.

（由 Victor Stinner 在 bpo-23404 中贡献。）

在 3.6.2 版更改.


Python 3.6.4 中的重要变化
=========================

The "PyExc_RecursionErrorInst" singleton that was part of the public
API has been removed as its members being never cleared may cause a
segfault during finalization of the interpreter. (Contributed by
Xavier de Gaye in bpo-22898 and bpo-30697.)


Python 3.6.5 中的重要变化
=========================

The "locale.localeconv()" function now sets temporarily the "LC_CTYPE"
locale to the "LC_NUMERIC" locale in some cases. (Contributed by
Victor Stinner in bpo-31900.)


Python 3.6.7 中的重要变化
=========================

"xml.dom.minidom" and mod:*xml.sax* modules no longer process external
entities by default. See also bpo-17239.

In 3.6.7 the "tokenize" module now implicitly emits a "NEWLINE" token
when provided with input that does not have a trailing new line.  This
behavior now matches what the C tokenizer does internally.
(Contributed by Ammar Askar in bpo-33899.)


Python 3.6.10 中的重要变化
==========================

出于重要的安全性考量，"asyncio.loop.create_datagram_endpoint()" 的
*reuse_address* 形参不再被支持。 这是由 UDP 中的套接字选项
"SO_REUSEADDR" 的行为导致的。 更多细节请参阅
"loop.create_datagram_endpoint()" 的文档。 （由 Kyle Stanley, Antoine
Pitrou 和 Yury Selivanov 在 bpo-37228 中贡献。。）


Notable changes in Python 3.6.13
================================

早先的 Python 版本允许使用 ";" 和 "&" 作为 "urllib.parse.parse_qs()"
和 "urllib.parse.parse_qsl()" 中 query 形参的分隔键。 出于安全考虑，也
为了遵循更新的 W3C 推荐设置，这已被改为只允许单个分隔键，默认为 "&"。
这一改变还会影响 "cgi.parse()" 和 "cgi.parse_multipart()" 因为它们在内
部使用了受影响的函数。 要了解更多细节，请查看它们各自的文档。 （由
Adam Goldschmidt, Senthil Kumaran 和 Ken Jin 在 bpo-42967 中贡献。）


Notable changes in Python 3.6.14
================================

A security fix alters the "ftplib.FTP" behavior to not trust the IPv4
address sent from the remote server when setting up a passive data
channel.  We reuse the ftp server IP address instead.  For unusual
code requiring the old behavior, set a
"trust_server_pasv_ipv4_address" attribute on your FTP instance to
"True".  (See bpo-43285)

The presence of newline or tab characters in parts of a URL allows for
some forms of attacks. Following the WHATWG specification that updates
RFC 3986, ASCII newline "\n", "\r" and tab "\t" characters are
stripped from the URL by the parser "urllib.parse()" preventing such
attacks. The removal characters are controlled by a new module level
variable "urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE". (See bpo-43882)
