创新互联Python教程：Python 3.5 有什么新变化

python 3.5 有什么新变化

Elvis Pranskevichus , Yury Selivanov

这篇文章介绍了 Python 3.5 相比 3.4 增加的新特性。 Python 3.5 发布于 2015 年 9 月 13 日。更完成的变化清单请参阅 changelog。

参见

PEP 478 - Python 3.5 发布计划

摘要 — 发布重点

新的语法特性：

PEP 492, 使用 async 和 await 语法实现协程。
PEP 465, 新的矩阵乘法运算符: a @ b.
PEP 448, 额外的解包通用化。

新的库模块：

typing: PEP 484 —— 类型注解.
zipapp: PEP 441 改进Python ZIP应用程序支持.

新的内置特性：

bytes % args, bytearray % args: PEP 461 — 为字节串和字节数组增加 % 格式化。
新增 bytes.hex(), bytearray.hex() 和 memoryview.hex() 方法。（由 Arnon Yaari 在 bpo-9951 中贡献。）
memoryview 现在支持元组索引（包括多维度）。（由 Antoine Pitrou 在 bpo-23632 中贡献。）
生成器具有一个新的 gi_yieldfrom 属性，它将返回 yield from 表达式所迭代的对象。（由 Benno Leslie 和 Yury Selivanov 在 bpo-24450 中贡献。）
现在当达到最大递归尝试时将引发新的 RecursionError 异常。（由 Georg Brandl 在 bpo-19235 中贡献。）

CPython 实现的改进：

当 LC_TYPE 语言区域为 POSIX 语言区域（即 C 语言区域）时，sys.stdin 和 sys.stdout 现在将使用 surrogateescape 错误处理句柄，而不是 strict 错误处理句柄。（由 Victor Stinner 在 bpo-19977 中贡献。）
.pyo 文件已不再被使用而是被替换为一个更灵活的方案即在 .pyc 名称中显式地包括优化级别。（参见 PEP 488 概览。）
内置与扩展模块现在将经过多阶段的过程被初始化，这类似于 Python 模块的加载方式。（参见 PEP 489 概览。）

标准库中的重大改进：

collections.OrderedDict 现在已用 C 实现，这使它的速度快了 4 到 100 部。
The ssl 模块获得了对内存 BIO 的支持，它使得 SSL 协议处理与网络 IO 实现了解耦。
新的 os.scandir() 函数提供了对于目录遍历更好和明显更快速的方式。
functools.lru_cache() 已经大部分用 C 重新实现，产生了更好的性能。
新的 subprocess.run() 函数提供了一个运行子进程的简便方式。
traceback 模块已被显著增强以改善性能和开发者便捷度。

安全改进：

SSLv3 目前在整个标准库中被禁用。它仍然可以通过手动实例化一个 ssl.SSLContext 来启用。（请参阅 bpo-22638 了解详情；此修改已向下移植到 CPython 3.4 和 2.7。）
HTTP cookie 解析现在将更严格，以防止潜在的注入攻击。（由 Antoine Pitrou 在 bpo-22796 中贡献。）

Windows改进：

使用新的 Windows 安装器替代了旧版 MSI。请参阅在Windows上使用 Python 了解详情。
Windows 编译版现在使用 Microsoft Visual C++ 14.0，扩展模块也应当使用同一版本。

请继续阅读有关针对用户的改变的完整清单，包括许多其他较小的改进、CPython 优化、弃用以及潜在的移植问题。

新的特性

PEP 492 - 使用 async 和 await 语法实现协程

PEP 492 通过添加可等待对象, 协程函数, 异步迭代和异步上下文管理器极大地改善了 Python 对异步编程的支持。

协程函数是使用新的 async def 语法来声明的:

 
 
 
   
  
  
  >>> async def coro():  
  
  
  ... return 'spam'

在协程函数内部，新的 await 表达式可用于挂起协程的执行直到其结果可用。任何对象都可以被等待，只要它通过定义 __await__() 方法实现了 awaitable 协议。

PEP 492 还增加了 async for 语句用于方便地迭代异步可迭代对象。

An example of a rudimentary HTTP client written using the new syntax:

 
 
 
   
  
  
  import asyncio  
  
  
    
  
  
  async def http_get(domain):  
  
  
   reader, writer = await asyncio.open_connection(domain, 80)  
  
  
    
  
  
   writer.write(b'\r\n'.join([  
  
  
   b'GET / HTTP/1.1',  
  
  
   b'Host: %b' % domain.encode('latin-1'),  
  
  
   b'Connection: close',  
  
  
   b'', b''  
  
  
   ]))  
  
  
    
  
  
   async for line in reader:  
  
  
   print('>>>', line)  
  
  
    
  
  
   writer.close()  
  
  
    
  
  
  loop = asyncio.get_event_loop()  
  
  
  try:  
  
  
   loop.run_until_complete(http_get('example.com'))  
  
  
  finally:  
  
  
   loop.close()

Similarly to asynchronous iteration, there is a new syntax for asynchronous context managers. The following script:

 
 
 
   
  
  
  import asyncio  
  
  
    
  
  
  async def coro(name, lock):  
  
  
   print('coro {}: waiting for lock'.format(name))  
  
  
   async with lock:  
  
  
   print('coro {}: holding the lock'.format(name))  
  
  
   await asyncio.sleep(1)  
  
  
   print('coro {}: releasing the lock'.format(name))  
  
  
    
  
  
  loop = asyncio.get_event_loop()  
  
  
  lock = asyncio.Lock()  
  
  
  coros = asyncio.gather(coro(1, lock), coro(2, lock))  
  
  
  try:  
  
  
   loop.run_until_complete(coros)  
  
  
  finally:  
  
  
   loop.close()

将输出：

 
 
 
   
  
  
  coro 2: waiting for lock  
  
  
  coro 2: holding the lock  
  
  
  coro 1: waiting for lock  
  
  
  coro 2: releasing the lock  
  
  
  coro 1: holding the lock  
  
  
  coro 1: releasing the lock

Note that both async for and async with can only be used inside a coroutine function declared with async def.

Coroutine functions are intended to be run inside a compatible event loop, such as the asyncio loop.

备注

在 3.5.2 版更改: Starting with CPython 3.5.2, __aiter__ can directly return asynchronous iterators. Returning an awaitable object will result in a PendingDeprecationWarning.

See more details in the 异步迭代器 documentation section.

参见

PEP 492 — 使用 async 和 await 语法实现协程

PEP 由 Yury Selivanov 撰写并实现

PEP 465 - 用于矩阵乘法的专用中缀运算符

PEP 465 adds the @ infix operator for matrix multiplication. Currently, no builtin Python types implement the new operator, however, it can be implemented by defining __matmul__(), __rmatmul__(), and __imatmul__() for regular, reflected, and in-place matrix multiplication. The semantics of these methods is similar to that of methods defining other infix arithmetic operators.

矩阵乘法在数学，科学，工程学的许多领域中是一种常见的操作，使用 @ 运算符可以编写更简洁的代码：

 
 
 
   
  
  
  S = (H @ beta - r).T @ inv(H @ V @ H.T) @ (H @ beta - r)

代替：

 
 
 
   
  
  
  S = dot((dot(H, beta) - r).T,  
  
  
   dot(inv(dot(dot(H, V), H.T)), dot(H, beta) - r))

NumPy 1.10 支持新的运算符：

 
 
 
   
  
  
  >>> import numpy  
  
  
    
  
  
  >>> x = numpy.ones(3)  
  
  
  >>> x  
  
  
  array([ 1., 1., 1.])  
  
  
    
  
  
  >>> m = numpy.eye(3)  
  
  
  >>> m  
  
  
  array([[ 1., 0., 0.],  
  
  
   [ 0., 1., 0.],  
  
  
   [ 0., 0., 1.]])  
  
  
    
  
  
  >>> x @ m  
  
  
  array([ 1., 1., 1.])

参见

PEP 465 — 用于矩阵乘法的专用中缀运算符

PEP 由 Nathaniel J. Smith 撰写，由 Benjamin Peterson 实现。

PEP 448 - Additional Unpacking Generalizations

PEP 448 extends the allowed uses of the * iterable unpacking operator and ** dictionary unpacking operator. It is now possible to use an arbitrary number of unpackings in function calls:

 
 
 
   
  
  
  >>> print(*[1], *[2], 3, *[4, 5])  
  
  
  1 2 3 4 5  
  
  
    
  
  
  >>> def fn(a, b, c, d):  
  
  
  ... print(a, b, c, d)  
  
  
  ...  
  
  
    
  
  
  >>> fn(**{'a': 1, 'c': 3}, **{'b': 2, 'd': 4})  
  
  
  1 2 3 4

Similarly, tuple, list, set, and dictionary displays allow multiple unpackings (see 表达式列表 and 字典显示):

 
 
 
   
  
  
  >>> *range(4), 4  
  
  
  (0, 1, 2, 3, 4)  
  
  
    
  
  
  >>> [*range(4), 4]  
  
  
  [0, 1, 2, 3, 4]  
  
  
    
  
  
  >>> {*range(4), 4, *(5, 6, 7)}  
  
  
  {0, 1, 2, 3, 4, 5, 6, 7}  
  
  
    
  
  
  >>> {'x': 1, **{'y': 2}}  
  
  
  {'x': 1, 'y': 2}

参见

PEP 448 — Additional Unpacking Generalizations

PEP 由 Joshua Landau 撰写，由 Neil Girdhar，Thomas Wouters 和 Joshua Landau 实现。

PEP 461 - percent formatting support for bytes and bytearray

PEP 461 adds support for the % interpolation operator to bytes and bytearray.

While interpolation is usually thought of as a string operation, there are cases where interpolation on bytes or bytearrays makes sense, and the work needed to make up for this missing functionality detracts from the overall readability of the code. This issue is particularly important when dealing with wire format protocols, which are often a mixture of binary and ASCII compatible text.

示例:

 
 
 
   
  
  
  >>> b'Hello %b!' % b'World'  
  
  
  b'Hello World!'  
  
  
    
  
  
  >>> b'x=%i y=%f' % (1, 2.5)  
  
  
  b'x=1 y=2.500000'

Unicode is not allowed for %b, but it is accepted by %a (equivalent of repr(obj).encode('ascii', 'backslashreplace')):

 
 
 
   
  
  
  >>> b'Hello %b!' % 'World'  
  
  
  Traceback (most recent call last):  
  
  
   File "", line 1, in   
  
  
  TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'  
  
  
    
  
  
  >>> b'price: %a' % '10€'  
  
  
  b"price: '10\\u20ac'"

Note that %s and %r conversion types, although supported, should only be used in codebases that need compatibility with Python 2.

参见

PEP 461 — Adding % formatting to bytes and bytearray

PEP 由 Ethan Furman 撰写，由 Neil Schemenauer 和 Ethan Furman 实现。

PEP 484 —— 类型注解

Function annotation syntax has been a Python feature since version 3.0 (PEP 3107), however the semantics of annotations has been left undefined.

Experience has shown that the majority of function annotation uses were to provide type hints to function parameters and return values. It became evident that it would be beneficial for Python users, if the standard library included the base definitions and tools for type annotations.

PEP 484 introduces a provisional module to provide these standard definitions and tools, along with some conventions for situations where annotations are not available.

For example, here is a simple function whose argument and return type are declared in the annotations:

 
 
 
   
  
  
  def greeting(name: str) -> str:  
  
  
   return 'Hello ' + name

While these annotations are available at runtime through the usual __annotations__ attribute, no automatic type checking happens at runtime. Instead, it is assumed that a separate off-line type checker (e.g. mypy) will be used for on-demand source code analysis.

The type system supports unions, generic types, and a special type named Any which is consistent with (i.e. assignable to and from) all types.

参见

typing 模块文档
PEP 484 —— 类型注解
PEP 由 Guido van Rossum，Jukka Lehtosalo 和 Łukasz Langa 撰写，由 Guido van Rossum 实现。
PEP 483 — 类型提示理论
PEP 由 Yury Selivanov 撰写

PEP 471 - os.scandir() function — a better and faster directory iterator

PEP 471 adds a new directory iteration function, os.scandir(), to the standard library. Additionally, os.walk() is now implemented using scandir, which makes it 3 to 5 times faster on POSIX systems and 7 to 20 times faster on Windows systems. This is largely achieved by greatly reducing the number of calls to os.stat() required to walk a directory tree.

Additionally, scandir returns an iterator, as opposed to returning a list of file names, which improves memory efficiency when iterating over very large directories.

The following example shows a simple use of os.scandir() to display all the files (excluding directories) in the given path that don’t start with '.'. The entry.is_file() call will generally not make an additional system call:

 
 
 
   
  
  
  for entry in os.scandir(path):  
  
  
   if not entry.name.startswith('.') and entry.is_file():  
  
  
   print(entry.name)

参见

PEP 471 — os.scandir() function — a better and faster directory iterator

PEP 由 Ben Hoyt 在 Victor Stinner 的帮助下撰写并实现

PEP 475: Retry system calls failing with EINTR

An errno.EINTR error code is returned whenever a system call, that is waiting for I/O, is interrupted by a signal. Previously, Python would raise InterruptedError in such cases. This meant that, when writing a Python application, the developer had two choices:

Ignore the InterruptedError.
Handle the InterruptedError and attempt to restart the interrupted system call at every call site.

The first option makes an application fail intermittently. The second option adds a large amount of boilerplate that makes the code nearly unreadable. Compare:

 
 
 
   
  
  
  print("Hello World")

和:

 
 
 
   
  
  
  while True:  
  
  
   try:  
  
  
   print("Hello World")  
  
  
   break  
  
  
   except InterruptedError:  
  
  
   continue

PEP 475 implements automatic retry of system calls on EINTR. This removes the burden of dealing with EINTR or InterruptedError in user code in most situations and makes Python programs, including the standard library, more robust. Note that the system call is only retried if the signal handler does not raise an exception.

Below is a list of functions which are now retried when interrupted by a signal:

open() 和 io.open();
faulthandler 模块的功能
os 函数: fchdir(), fchmod(), fchown(), fdatasync(), fstat(), fstatvfs(), fsync(), ftruncate(), mkfifo(), mknod(), open(), posix_fadvise(), posix_fallocate(), pread(), pwrite(), read(), readv(), sendfile(), wait3(), wait4(), wait(), waitid(), waitpid(), write(), writev();
特例: os.close() 和 os.dup2() 现在会忽略 EINTR 错误; 不重试系统调用（请参阅PEP了解基本原理）
select 函数: devpoll.poll(), epoll.poll(), kqueue.control(), poll.poll(), select();
socket 类的方法: accept(), connect() （除了非阻塞套接字）, recv(), recvfrom(), recvmsg(), send(), sendall(), sendmsg(), sendto();
signal.sigtimedwait() 和 signal.sigwaitinfo();
time.sleep().

参见

PEP 475 — Retry system calls failing with EINTR

PEP and implementation written by Charles-François Natali and Victor Stinner, with the help of Antoine Pitrou (the French connection).

PEP 479: Change StopIteration handling inside generators

The interaction of generators and StopIteration in Python 3.4 and earlier was sometimes surprising, and could conceal obscure bugs. Previously, StopIteration raised accidentally inside a generator function was interpreted as the end of the iteration by the loop construct driving the generator.

PEP 479 changes the behavior of generators: when a StopIteration exception is raised inside a generator, it is replaced with a RuntimeError before it exits the generator frame. The main goal of this change is to ease debugging in the situation where an unguarded next() call raises StopIteration and causes the iteration controlled by the generator to terminate silently. This is particularly pernicious in combination with the yield from construct.

This is a backwards incompatible change, so to enable the new behavior, a __future__ import is necessary:

 
 
 
   
  
  
  >>> from __future__ import generator_stop  
  
  
    
  
  
  >>> def gen():  
  
  
  ... next(iter([]))  
  
  
  ... yield  
  
  
  ...  
  
  
  >>> next(gen())  
  
  
  Traceback (most recent call last):  
  
  
   File "", line 2, in gen  
  
  
  StopIteration  
  
  
    
  
  
  The above exception was the direct cause of the following exception:  
  
  
    
  
  
  Traceback (most recent call last):  
  
  
   File "", line 1, in   
  
  
  RuntimeError: generator raised StopIteration

Without a __future__ import, a PendingDeprecationWarning will be raised whenever a StopIteration exception is raised inside a generator.

参见

PEP 479 — Change StopIteration handling inside generators

PEP 由 Chris Angelico 和 Guido van Rossum 撰写，由 Chris Angelico，Yury Selivanov 和 Nick Coghlan 实现。

PEP 485: A function for testing approximate equality

PEP 485 adds the math.isclose() and cmath.isclose() functions which tell whether two values are approximately equal or “close” to each other. Whether or not two values are considered close is determined according to given absolute and relative tolerances. Relative tolerance is the maximum allowed difference between isclose arguments, relative to the larger absolute value:

 
 
 
   
  
  
  >>> import math  
  
  
  >>> a = 5.0  
  
  
  >>> b = 4.99998  
  
  
  >>> math.isclose(a, b, rel_tol=1e-5)  
  
  
  True  
  
  
  >>> math.isclose(a, b, rel_tol=1e-6)  
  
  
  False

It is also possible to compare two values using absolute tolerance, which must be a non-negative value:

 
 
 
   
  
  
  >>> import math  
  
  
  >>> a = 5.0  
  
  
  >>> b = 4.99998  
  
  
  >>> math.isclose(a, b, abs_tol=0.00003)  
  
  
  True  
  
  
  >>> math.isclose(a, b, abs_tol=0.00001)  
  
  
  False

参见

PEP 485 —— 用于测试近似相等的函数

PEP 由 Christopher Barker 撰写，由 Chris Barker 和 Tal Einat 实现。

PEP 486: Make the Python Launcher aware of virtual environments

PEP 486 makes the Windows launcher (see PEP 397) aware of an active virtual environment. When the default interpreter would be used and the VIRTUAL_ENV environment variable is set, the interpreter in the virtual environment will be used.

参见

PEP 486 — Make the Python Launcher aware of virtual environments

PEP 由 Paul Moore 撰写并实现

PEP 488: Elimination of PYO files

PEP 488 does away with the concept of .pyo files. This means that .pyc files represent both unoptimized and optimized bytecode. To prevent the need to constantly regenerate bytecode files, .pyc files now have an optional opt- tag in their name when the bytecode is optimized. This has the side-effect of no more bytecode file name clashes when running under either -O or -OO. Consequently, bytecode files generated from -O, and -OO may now exist simultaneously. importlib.util.cache_from_source() has an updated API to help with this change.

参见

PEP 488 — Elimination of PYO files

PEP 由 Brett Cannon 撰写并实现。

PEP 489: Multi-phase extension module initialization

PEP 489 updates extension module initialization to take advantage of the two step module loading mechanism introduced by PEP 451 in Python 3.4.

This change brings the import semantics of extension modules that opt-in to using the new mechanism much closer to those of Python source and bytecode modules, including the ability to use any valid identifier as a module name, rather than being restricted to ASCII.

参见

PEP 489 — Multi-phase extension module initialization

PEP 由 Petr Viktorin , Stefan Behnel 和 Nick Coghlan 撰写，由 Petr Viktorin 实现。

其他语言特性修改

对Python 语言核心进行的小改动：

Added the "namereplace" error handlers. The "backslashreplace" error handlers now work with decoding and translating. (Contributed by Serhiy Storchaka in bpo-19676 and bpo-22286.)
The -b option now affects comparisons of bytes with int. (Contributed by Serhiy Storchaka in bpo-23681.)
New Kazakh kz1048 and Tajik koi8_t codecs. (Contributed by Serhiy Storchaka in bpo-22682 and bpo-22681.)
Property docstrings are now writable. This is especially useful for collections.namedtuple() docstrings. (Contributed by Berker Peksag in bpo-24064.)
Circular imports involving relative imports are now supported. (Contributed by Brett Cannon and Antoine Pitrou in bpo-17636.)

新增模块

typing

The new typing provisional module provides standard definitions and tools for function type annotations. See Type Hints for more information.

zipapp

The new zipapp module (specified in PEP 441) provides an API and command line tool for creating executable Python Zip Applications, which were introduced in Python 2.6 in bpo-1739468, but which were not well publicized, either at the time or since.

With the new module, bundling your application is as simple as putting all the files, including a __main__.py file, into a directory myapp and running:

 
 
 
   
  
  
  $ python -m zipapp myapp  
  
  
  $ python myapp.pyz

The module implementation has been contributed by Paul Moore in bpo-23491.

参见

PEP 441 — Improving Python ZIP Application Support

改进的模块

argparse

The ArgumentParser class now allows disabling abbreviated usage of long options by setting allow_abbrev to False. (Contributed by Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson in bpo-14910.)

asyncio

Since the asyncio module is provisional, all changes introduced in Python 3.5 have also been backported to Python 3.4.x.

Notable changes in the asyncio module since Python 3.4.0:

New debugging APIs: loop.set_debug() and loop.get_debug() methods. (Contributed by Victor Stinner.)
The proactor event loop now supports SSL. (Contributed by Antoine Pitrou and Victor Stinner in bpo-22560.)
A new loop.is_closed() method to check if the event loop is closed. (Contributed by Victor Stinner in bpo-21326.)
A new loop.create_task() to conveniently create and schedule a new Task for a coroutine. The create_task method is also used by all asyncio functions that wrap coroutines into tasks, such as asyncio.wait(), asyncio.gather(), etc. (Contributed by Victor Stinner.)
A new transport.get_write_buffer_limits() method to inquire for high- and low- water limits of the flow control. (Contributed by Victor Stinner.)
The async() function is deprecated in favor of ensure_future(). (Contributed by Yury Selivanov.)
New loop.set_task_factory() and loop.get_task_factory() methods to customize the task factory that loop.create_task() method uses. (Contributed by Yury Selivanov.)
New Queue.join() and Queue.task_done() queue methods. (Contributed by Victor Stinner.)
The JoinableQueue class was removed, in favor of the asyncio.Queue class. (Contributed by Victor Stinner.)

3.5.1 中的更新：

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.)
新增 run_coroutine_threadsafe() 函数用于从其他线程向事件循环提交协程。（由 Vincent Michel 贡献。）
新增 Transport.is_closing() 方法用于检查传输是否正在关闭或已经关闭。（由 Yury Selivanov 贡献。）
loop.create_server() 方法现在可以接受一个主机列表。（由 Yann Sionneau 贡献。）

3.5.2 中的更新：

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.create_connection() and loop.create_server() methods are optimized to avoid calling the system getaddrinfo function if the address is already resolved. (Contributed by A. Jesse Jiryu Davis.)
The loop.sock_connect(sock, address) no longer requires the address to be resolved prior to the call. (Contributed by A. Jesse Jiryu Davis.)

bz2

The BZ2Decompressor.decompress method now accepts an optional max_length argument to limit the maximum size of decompressed data. (Contributed by Nikolaus Rath in bpo-15955.)

cgi

The FieldStorage class now supports the context manager protocol. (Contributed by Berker Peksag in bpo-20289.)

cmath

A new function isclose() provides a way to test for approximate equality. (Contributed by Chris Barker and Tal Einat in bpo-24270.)

code

The InteractiveInterpreter.showtraceback() method now prints the full chained traceback, just like the interactive interpreter. (Contributed by Claudiu Popa in bpo-17442.)

collections

The OrderedDict class is now implemented in C, which makes it 4 to 100 times faster. (Contributed by Eric Snow in bpo-16991.)

OrderedDict.items(), OrderedDict.keys(), OrderedDict.values() views now support reversed() iteration. (Contributed by Serhiy Storchaka in bpo-19505.)

The deque class now defines index(), insert(), and copy(), and supports the + and * operators. This allows deques to be recognized as a MutableSequence and improves their substitutability for lists. (Contributed by Raymond Hettinger in bpo-23704.)

Docstrings produced by namedtuple() can now be updated:

 
 
 
   
  
  
  Point = namedtuple('Point', ['x', 'y'])  
  
  
  Point.__doc__ += ': Cartesian coodinate'  
  
  
  Point.x.__doc__ = 'abscissa'  
  
  
  Point.y.__doc__ = 'ordinate'

（由 Berker Peksag 在 bpo-24064 中贡献。）

The UserString class now implements the __getnewargs__(), __rmod__(), casefold(), format_map(), isprintable(), and maketrans() methods to match the corresponding methods of str. (Contributed by Joe Jevnik in bpo-22189.)

collections.abc

The Sequence.index() method now accepts start and stop arguments to match the corresponding methods of tuple, list, etc. (Contributed by Devin Jeanpierre in bpo-23086.)

A new Generator abstract base class. (Contributed by Stefan Behnel in bpo-24018.)

New Awaitable, Coroutine, AsyncIterator, and AsyncIterable abstract base classes. (Contributed by Yury Selivanov in bpo-24184.)

For earlier Python versions, a backport of the new ABCs is available in an external PyPI package.

compileall

A new compileall option, -j *N*, allows running N workers simultaneously to perform parallel bytecode compilation. The compile_dir() function has a corresponding workers parameter. (Contributed by Claudiu Popa in bpo-16104.)

Another new option, -r, allows controlling the maximum recursion level for subdirectories. (Contributed by Claudiu Popa in bpo-19628.)

The -q command line option can now be specified more than once, in which case all output, including errors, will be suppressed. The corresponding quiet parameter in compile_dir(), compile_file(), and compile_path() can now accept an integer value indicating the level of output suppression. (Contributed by Thomas Kluyver in bpo-21338.)

concurrent.futures

The Executor.map() method now accepts a chunksize argument to allow batching of tasks to improve performance when ProcessPoolExecutor() is used. (Contributed by Dan O’Reilly in bpo-11271.)

The number of workers in the ThreadPoolExecutor constructor is optional now. The default value is 5 times the number of CPUs. (Contributed by Claudiu Popa in bpo-21527.)

configparser

configparser now provides a way to customize the conversion of values by specifying a dictionary of converters in the ConfigParser constructor, or by defining them as methods in ConfigParser subclasses. Converters defined in a parser instance are inherited by its section proxies.

示例:

 
 
 
   
  
  
  >>> import configparser  
  
  
  >>> conv = {}  
  
  
  >>> conv['list'] = lambda v: [e.strip() for e in v.split() if e.strip()]  
  
  
  >>> cfg = configparser.ConfigParser(converters=conv)  
  
  
  >>> cfg.read_string("""  
  
  
  ... [s]  
  
  
  ... list = a b c d e f g  
  
  
  ... """)  
  
  
  >>> cfg.get('s', 'list')  
  
  
  'a b c d e f g'  
  
  
  >>> cfg.getlist('s', 'list')  
  
  
  ['a', 'b', 'c', 'd', 'e', 'f', 'g']  
  
  
  >>> section = cfg['s']  
  
  
  >>> section.getlist('list')  
  
  
  ['a', 'b', 'c', 'd', 'e', 'f', 'g']

（由 Łukasz Langa 在 bpo-18159 中贡献。）

contextlib

The new redirect_stderr() context manager (similar to redirect_stdout()) makes it easier for utility scripts to handle inflexible APIs that write their output to sys.stderr and don’t provide any options to redirect it:

 
 
 
   
  
  
  >>> import contextlib, io, logging  
  
  
  >>> f = io.StringIO()  
  
  
  >>> with contextlib.redirect_stderr(f):  
  
  
  ... logging.warning('warning')  
  
  
  ...  
  
  
  >>> f.getvalue()  
  
  
  'WARNING:root:warning\n'

（由 Berker Peksag 在 bpo-22389 中贡献。）

csv

The writerow() method now supports arbitrary iterables, not just sequences. (Contributed by Serhiy Storchaka in bpo-23171.)

curses

The new update_lines_cols() function updates the LINES and COLS environment variables. This is useful for detecting manual screen resizing. (Contributed by Arnon Yaari in bpo-4254.)

dbm

dumb.open always creates a new database when the flag has the value "n". (Contributed by Claudiu Popa in bpo-18039.)

difflib

The charset of HTML documents generated by HtmlDiff.make_file() can now be customized by using a new charset keyword-only argument. The default charset of HTML document changed from "ISO-8859-1" to "utf-8". (Contributed by Berker Peksag in bpo-2052.)

The diff_bytes() function can now compare lists of byte strings. This fixes a regression from Python 2. (Contributed by Terry J. Reedy and Greg Ward in bpo-17445.)

distutils

Both the build and build_ext commands now accept a -j option to enable parallel building of extension modules. (Contributed by Antoine Pitrou in bpo-5309.)

The distutils module now supports xz compression, and can be enabled by passing xztar as an argument to bdist --format. (Contributed by Serhiy Storchaka in bpo-16314.)

doctest

The DocTestSuite() function returns an empty unittest.TestSuite if module contains no docstrings, instead of raising ValueError. (Contributed by Glenn Jones in bpo-15916.)

email

A new policy option Policy.mangle_from_ controls whether or not lines that start with "From " in email bodies are prefixed with a ">" character by generators. The default is True for compat32 and False for all other policies. (Contributed by Milan Oberkirch in bpo-20098.)

A new Message.get_content_disposition() method provides easy access to a canonical value for the Content-Disposition header. (Contributed by Abhilash Raj in bpo-21083.)

A new policy option EmailPolicy.utf8 can be set to True to encode email headers using the UTF-8 charset instead of using encoded words. This allows Messages to be formatted according to RFC 6532 and used with an SMTP server that supports the RFC 6531 SMTPUTF8 extension. (Contributed by R. David Murray in bpo-24211.)

The mime.text.MIMEText constructor now accepts a charset.Charset instance. (Contributed by Claude Paroz and Berker Peksag in bpo-16324.)

enum

The Enum callable has a new parameter start to specify the initial number of enum values if only names are provided:

 
 
 
   
  
  
  >>> Animal = enum.Enum('Animal', 'cat dog', start=10)  
  
  
  >>> Animal.cat  
  
  
    
  
  
  >>> Animal.dog

（由 Ethan Furman 在 bpo-21706 中贡献。）

faulthandler

The enable(), register(), dump_traceback() and dump_traceback_later() functions now accept file descriptors in addition to file-like objects. (Contributed by Wei Wu in bpo-23566.)

functools

Most of the lru_cache() machinery is now implemented in C, making it significantly faster. (Contributed by Matt Joiner, Alexey Kachayev, and Serhiy Storchaka in bpo-14373.)

glob

The iglob() and glob() functions now support recursive search in subdirectories, using the "**" pattern. (Contributed by Serhiy Storchaka in bpo-13968.)

gzip

The mode argument of the GzipFile constructor now accepts "x" to request exclusive creation. (Contributed by Tim Heaney in bpo-19222.)

heapq

Element comparison in merge() can now be customized by passing a key function in a new optional key keyword argument, and a new optional reverse keyword argument can be used to reverse element comparison:

 
 
 
   
  
  
  >>> import heapq  
  
  
  >>> a = ['9', '777', '55555']  
  
  
  >>> b = ['88', '6666']  
  
  
  >>> list(heapq.merge(a, b, key=len))  
  
  
  ['9', '88', '777', '6666', '55555']  
  
  
  >>> list(heapq.merge(reversed(a), reversed(b), key=len, reverse=True))  
  
  
  ['55555', '6666', '777', '88', '9']

（由 Raymond Hettinger 在 bpo-13742 中贡献。）

http

A new HTTPStatus enum that defines a set of HTTP status codes, reason phrases and long descriptions written in English. (Contributed by Demian Brecht in bpo-21793.)

http.client

HTTPConnection.getresponse() now raises a RemoteDisconnected exception when a remote server connection is closed unexpectedly. Additionally, if a ConnectionError (of which RemoteDisconnected is a subclass) is raised, the client socket is now closed automatically, and will reconnect on the next request:

 
 
 
   
  
  
  import http.client  
  
  
  conn = http.client.HTTPConnection('www.python.org')  
  
  
  for retries in range(3):  
  
  
   try:  
  
  
   conn.request('GET', '/')  
  
  
   resp = conn.getresponse()  
  
  
   except http.client.RemoteDisconnected:  
  
  
   pass

（由 Martin Panter 在 bpo-3566 中贡献。）

idlelib 与 IDLE

Since idlelib implements the IDLE shell and editor and is not intended for import by other programs, it gets improvements with every release. See Lib/idlelib/NEWS.txt for a cumulative list of changes since 3.4.0, as well as changes made in future 3.5.x releases. This file is also available from the IDLE Help ‣ About IDLE dialog.

imaplib

The IMAP4 class now supports the context manager protocol. When used in a with statement, the IMAP4 LOGOUT command will be called automatically at the end of the block. (Contributed by Tarek Ziadé and Serhiy Storchaka in bpo-4972.)

The imaplib module now supports RFC 5161 (ENABLE Extension) and RFC 6855 (UTF-8 Support) via the IMAP4.enable() method. A new IMAP4.utf8_enabled attribute tracks whether or not RFC 6855 support is enabled. (Contributed by Milan Oberkirch, R. David Murray, and Maciej Szulik in bpo-21800.)

The imaplib module now automatically encodes non-ASCII string usernames and passwords using UTF-8, as recommended by the RFCs. (Contributed by Milan Oberkirch in bpo-21800.)

imghdr

The what() function now recognizes the OpenEXR format (contributed by Martin Vignali and Claudiu Popa in bpo-20295), and the WebP format (contributed by Fabrice Aneche and Claudiu Popa in bpo-20197.)

importlib

The util.LazyLoader class allows for lazy loading of modules in applications where startup time is important. (Contributed by Brett Cannon in bpo-17621.)

The abc.InspectLoader.source_to_code() method is now a static method. This makes it easier to initialize a module object with code compiled from a string by running exec(code, module.__dict__). (Contributed by Brett Cannon in bpo-21156.)

The new util.module_from_spec() function is now the preferred way to create a new module. As opposed to creating a types.ModuleType instance directly, this new function will set the various import-controlled attributes based on the passed-in spec object. (Contributed by Brett Cannon in bpo-20383.)

inspect

Both the Signature and Parameter classes are now picklable and hashable. (Contributed by Yury Selivanov in bpo-20726 and bpo-20334.)

A new BoundArguments.apply_defaults() method provides a way to set default values for missing arguments:

 
 
 
   
  
  
  >>> def foo(a, b='ham', *args): pass  
  
  
  >>> ba = inspect.signature(foo).bind('spam')  
  
  
  >>> ba.apply_defaults()  
  
  
  >>> ba.arguments  
  
  
  OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())])

（由 Yury Selivanov 在 bpo-24190 中贡献。）

A new class method Signature.from_callable() makes subclassing of Signature easier. (Contributed by Yury Selivanov and Eric Snow in bpo-17373.)

The signature() function now accepts a follow_wrapped optional keyword argument, which, when set to False, disables automatic following of __wrapped__ links. (Contributed by Yury Selivanov in bpo-20691.)

A set of new functions to inspect coroutine functions and coroutine objects has been added: iscoroutine(), iscoroutinefunction(), isawaitable(), getcoroutinelocals(), and getcoroutinestate(). (Contributed by Yury Selivanov in bpo-24017 and bpo-24400.)

The stack(), trace(), getouterframes(), and getinnerframes() functions now return a list of named tuples. (Contributed by Daniel Shahaf in bpo-16808.)

io

A new BufferedIOBase.readinto1() method, that uses at most one call to the underlying raw stream’s RawIOBase.read() or RawIOBase.readinto() methods. (Contributed by Nikolaus Rath in bpo-20578.)

ipaddress

Both the IPv4Network and IPv6Network classes now accept an (address, netmask) tuple argument, so as to easily construct network objects from existing addresses:

 
 
 
   
  
  
  >>> import ipaddress  
  
  
  >>> ipaddress.IPv4Network(('127.0.0.0', 8))  
  
  
  IPv4Network('127.0.0.0/8')  
  
  
  >>> ipaddress.IPv4Network(('127.0.0.0', '255.0.0.0'))  
  
  
  IPv4Network('127.0.0.0/8')

（由 Peter Moody 和 Antoine Pitrou 在 bpo-16531 中贡献。）

A new reverse_pointer attribute for the IPv4Network and IPv6Network classes returns the name of the reverse DNS PTR record:

 
 
 
   
  
  
  >>> import ipaddress
              
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