# Python 3.5 有什么新变化

编者:

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

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。 更完整的变化清单请参阅 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。

一个使用新语法编写的基本 HTTP 客户端示例:

    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()

与异步迭代类似，增加了用于异步上下文管理器的新语法。 以下代码:

    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

请注意 `async for` 和 `async with` 都只能在通过 `async def` 声明的协程函数中使用。

协程函数应当在兼容的事件循环内部运行，例如 asyncio 循环。

备注

在 3.5.2 版本发生变更: 从 CPython 3.5.2 开始，`__aiter__` 可以直接返回 异步迭代器。 返回 awaitable 对象将会导致 `PendingDeprecationWarning`。

详情参见文档的 异步迭代器 一节。

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 增加了用于矩阵乘法的 `@` 中缀运算符。 目前，还没有内置的 Python 类型实现这个新运算符，不过，它可通过定义 `__matmul__()`, `__rmatmul__()` 和 `__imatmul__()` 分别用于常规、反射和原地矩阵乘法来实现。 这些方法的语义与定义其他中缀算术运算符的方法类似。

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 - 进一步的解包标准化

PEP 448 扩展了 `*` 可迭代对象解包操作符和 `**` 字典解包操作符的允许使用范围。 现在将可以在 函数调用 中使用任意数量的解包操作:

    >>> 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

类似地，元组、列表、集合与字典表示形式也允许多重解包 (参见 表达式列表 和 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 -- 进一步的解包标准化

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

### PEP 461 - 针对 bytes 和 bytearray 的百分号格式化支持

PEP 461 增加了 `%` 插值运算符 对 `bytes` 和 `bytearray` 的支持。

虽然插值通常被认为是一种字符串操作，但在某些情况下针对 `bytes` 或 `bytearrays` 的插值操作也是有意义，而弥补这种功能缺失所需的工作可能会影响代码的整体可读性。 在处理通常会混合二进制和 ASCII 兼容文本的 wire 格式化协议时，这个问题尤为重要。

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 对于 `%b` 来说是不允许的，但对 `%a` 来说则是可接受的 (等价于 `repr(obj).encode('ascii', 'backslashreplace')`):

    >>> b'Hello %b!' % 'World'
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'

    >>> b'price: %a' % '10€'
    b"price: '10\\u20ac'"

请注意 `%s` 和 `%r` 转换类型虽然受到支持，但应当只被用于需要与 Python 2 保持兼容性的代码中。

参见

PEP 461 -- 为 bytes 和 bytearray 添加 % 格式化

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

### PEP 484 —— 类型提示

函数标注语法自 3.0 版起即已成为 Python 的特性 (PEP 3107)，标注的语义尚未得到定义。

经验表明大多数函数标注的使用都是为了向函数形参和返回值提供类型提示。 很显然如果标准库可以包括用于类型标注的基本定义和工具，对 Python 用户来说将大有裨益。

PEP 484 引入了一个 暂定模块 来提供这些标准定义和工具，以及针对标注不可用的场合的一些惯例。

例如，以下是一个在标注中声明了参数和返回值类型的简单函数:

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

虽然这些标注可在运行时通过常用的 `__annotations__` 属性来访问，但是 不会在运行时执行任何类型检查。 相应地，应该有一个单独的离线版类型检查器 (例如 mypy) 被用来按需执行源代码分析。

类型系统支持合并、泛型类型以及名为 `Any` 的能够适用于所有类型（即作为赋值的来源和目标）的特殊类型。

参见

- `typing` 模块文档

- PEP 484 —— 类型提示

    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() 函数 -- 一个更好且更快的目录迭代器

PEP 471 向标准库添加了一个新的目录迭代函数 `os.scandir()`。 此外，`os.walk()` 现在是使用 `scandir` 来实现，这使它在 POSIX 系统上可提速 3 至 5 倍而在 Windows 系统上可提速 7 至 20 倍。 这样的效果主要是通过大幅减少遍历目录树所需调用 `os.stat()` 的次数来达成的。

此外，`scandir` 是返回一个迭代器，而不是返回一个文件名列表，这提升了迭代非常大的目录时的内存效率。

下面的例子演示了 `os.scandir()` 的简单用法，显示给定 path 中所有不以 `'.'` 开头的文件（不包括目录）。 `entry.is_file()` 调用通常不会执行额外的系统调用:

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

参见

PEP 471 -- os.scandir() 函数 -- 一个更好且更快的目录迭代器

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

### PEP 475: 重试返回 EINTR 失败码的系统调用

当一个正在等待 I/O 的系统调用被信号所中断时将会返回一个 `errno.EINTR` 错误码。 在之前版本中，Python 会在这种情况下引发 `InterruptedError`。 这意味着在编写 Python 应用程序时，开发者有两种选择：

1. 忽略 `InterruptedError`。

2. 处理 `InterruptedError` 并在每个调用位置尝试重新启动被中断的系统调用。

第一个选项会使应用程序中途出错。 第二个选项添加了大量的额外处理使得代码几乎不可读。 比较:

    print("Hello World")

和:

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

PEP 475 实现了在 `EINTR` 时自动重试系统调用。 这移除了大部分场合下在用户代码中处理 `EINTR` 或 `InterruptedError` 的负担，并使得 Python 程序，包括标准库的程序更为健壮。 请注意只有在信号处理句柄未引发异常时系统调用才会被重试。

以下是现在当被信号中断时会被重试的函数的列表：

- `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()`;

- 特殊情况: `os.close()` 和 `os.dup2()` 现在会忽略 `EINTR` 错误；系统调用将不被重试（请参阅 PEP 了解相关的理由）；

- `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 -- 重试返回 EINTR 失败码的系统调用

  PEP 和具体实现由 Charles-François Natali 和 Victor Stinner 撰写，并获得 Antoine Pitrou 的协助（同为法国人）。

### PEP 479：更改生成器内部的 StopIteration 处理

生成器与 `StopIteration` 的交互在 Python 3.4 及更早版本中有时会令人惊讶，并可能隐藏难以觉察的程序错误。 在之前版本中，一个生成器函数内部意外引发的 `StopIteration` 会被驱动该生成器的循环构造解读为迭代的结束。

PEP 479 更改了生成器的行为：当一个 `StopIteration` 异常在生成器内部被引发时，它会在其退出生成器所在帧时被替换为 `RuntimeError`。 这一更改的主要目的是方便在无防护的 `next()` 调用引发了 `StopIteration` 并导致生成器所控制的迭代静默地终结的情况下进行调试。 此情况在与 `yield from` 构造相结合时会特别令人困扰。

这是一个向下不兼容的更改，所以想要启用这个新行为，必须执行 __future__ 导入:

    >>> from __future__ import generator_stop

    >>> def gen():
    ...     next(iter([]))
    ...     yield
    ...
    >>> next(gen())
    Traceback (most recent call last):
      File "<stdin>", line 2, in gen
    StopIteration

    The above exception was the direct cause of the following exception:

    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    RuntimeError: generator raised StopIteration

如果未执行 `__future__` 导入，当在生成器内部引发 `StopIteration` 异常时将导致 `PendingDeprecationWarning` 被引发。

参见

PEP 479 -- 更改生成器内部的 StopIteration 处理

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

### PEP 485：用于测试近似相等的函数

PEP 485 增加了 `math.isclose()` 和 `cmath.isclose()` 函数用于检测两个值是否近似相等或称“接近”。 两个值是否接近是根据给定的绝对和相对范围来确定的。 相对范围是 `isclose` 参数之间的最大允许差值，即相对于较大的那个绝对数值的距离:

    >>> 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

也可以使用绝对范围来比较两个值，它必须是一个非负数值:

    >>> 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：让 Python 启动器识别虚拟环境

PEP 486 让 Windows 版启动器 (参见 PEP 397) 能够识别激活的虚拟环境。 当要使用默认解释器并且设置了 `VIRTUAL_ENV` 环境变量时，将使用虚拟环境中的解释器。

参见

PEP 486 -- 让 Python 启动器识别虚拟环境

  PEP 由 Paul Moore 撰写并实现

### PEP 488：去除 PYO 文件

PEP 488 取消了 `.pyo` 文件的概念。 这意味着 `.pyc` 文件将同时代表未优化和已优化的字节码。 为了防止经常需要重新生成字节码文件，现在 `.pyc` 文件可以在其名称中设置可选的 `opt-` 标签来表示已优化字节码。 该设置的附带效果是当以 `-O` 和 `-OO` 运行时将不会有字节码文件名冲突。 其结果是，使用 `-O` 和 `-OO` 生成的字节码现在可以同时存在。 `importlib.util.cache_from_source()` 专门针对此项变化更新了 API。

参见

PEP 488 -- 去除 PYO 文件

  PEP 由 Brett Cannon 撰写并实现。

### PEP 489：多阶段扩展模块初始化

PEP 489 更新了扩展模块初始化操作以便利用 Python 3.4 中通过 PEP 451 引入的两步模块加载机制的优势。

这一变化让选择使用新机制的扩展模块的导入语义与 Python 源代码和字节码模块的更为接近，包括可以使用任何有效标识符作为模块名称，而不是仅限于 ASCII。

参见

PEP 489 -- 多阶段扩展模块初始化

  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：

- 增加了 `"namereplace"` 错误处理句柄。 `"backslashreplace"` 错误处理句柄现在可用于解码和转译。 （由 Serhiy Storchaka 在 bpo-19676 和 bpo-22286 中贡献。）

- 现在 `-b` 选项会影响 `bytes` 与 `int` 的比较。 （由 Serhiy Storchaka 在 bpo-23681 中贡献。）

- 新增 Kazakh `kz1048` 和 Tajik `koi8_t` 编解码器。 （由 Serhiy Storchaka 在 bpo-22682 和 bpo-22681 中贡献。）

- 特征属性文档字符串现在将是可写的。 这对于 `collections.namedtuple()` 文档字符串特别适用。 （由 Berker Peksag 在 bpo-24064 中贡献。）

- 涉及相对导入的环形导入现在已受到支持。 （由 Brett Cannon 和 Antoine Pitrou 在 bpo-17636 中贡献。）

## 新增模块

### typing

新增的 `typing` 暂定 模块提供了对函数类型标注的标准定义和工具。 详情参见 类型提示。

### zipapp

新增的 `zipapp` 模块（在 PEP 441 中描述）提供了用于创建可执行 Python Zip 应用程序的 API 和命令行工具，它是根据 bpo-1739468 在 Python 2.6 中引入的，但在当时和之后都没有足够的推广。

使用这个新模块，想要打包你的应用程序只需简单地将所有文件，包括一个 `__main__.py` 文件放到一个目录 `myapp` 中并运行：

    $ python -m zipapp myapp
    $ python myapp.pyz

该模块的实现由 Paul Moore 在 bpo-23491 中贡献。

参见

PEP 441 -- 改进 Python ZIP 应用程序支持

## 改进的模块

### argparse

现在 `ArgumentParser` 类允许通过将 allow_abbrev 设为 `False` 来禁用长选项的 缩写用法。 （由 Jonathan Paugh, Steven Bethard, paul j3 和 Daniel Eriksson 在 bpo-14910 中贡献。）

### asyncio

由于 `asyncio` 模块处于 暂定状态，在 Python 3.5 中引入的所有改变都已被向下移植到 Python 3.4.x。

自 Python 3.4.0 开始 `asyncio` 模块中的重要变化：

- 新增的调试 API: `loop.set_debug()` 和 `loop.get_debug()` 方法。 （由 Victor Stinner 贡献。）

- 现在 proactor 事件循环已支持 SSL。 （由 Antoine Pitrou 和 Victor Stinner 在 bpo-22560 中贡献。）

- 新增的 `loop.is_closed()` 方法可检测事件循环是否已关闭。 （由 Victor Stinner 在 bpo-21326 中贡献。）.)

- 新增的 `loop.create_task()` 用来方便地新建一个 `Task` 并将其排入协程的计划任务。 `create_task` 方法还可供所有将协程包装为任务的 asyncio 函数使用，例如 `asyncio.wait()`, `asyncio.gather()` 等。 （由 Victor Stinner 贡献。）

- 新增的 `transport.get_write_buffer_limits()` 方法用于查询流程控制的 高 与 低 水位限制。 （由 Victor Stinner 贡献。）

- `async()` 函数已被弃用并由 `ensure_future()` 取代。 （由 Yury Selivanov 贡献。）

- 新增 `loop.set_task_factory()` 和 `loop.get_task_factory()` 方法用于自定义供 `loop.create_task()` 方法使用的任务工厂。 （由 Yury Selivanov 贡献。）

- 新增 `Queue.join()` 和 `Queue.task_done()` 队列方法。 （由 Victor Stinner 贡献。）

- 移除了 `JoinableQueue` 类，建议改用 `asyncio.Queue` 类。 （由 Victor Stinner 贡献。）

3.5.1 中的更新：

- `ensure_future()` 函数以及所有用到它的函数，比如 `loop.run_until_complete()`，现在将接受所有种类的 可等待对象。 （由 Yury Selivanov 贡献。）

- 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：

- 新增 `loop.create_future()` 方法用来创建 Future 对象。 这允许替代性的事件循环实现，比如 uvloop，以提供更快速的 `asyncio.Future` 实现。 （由 Yury Selivanov 贡献。）

- 新增 `loop.get_exception_handler()` 方法用于获取当前异常处理句柄。 （由 Yury Selivanov 贡献。）

- 新增 `StreamReader.readuntil()` 方法用于从流读取数据直到出现作为分隔符的字节序列。 （由 Mark Korenberg 贡献。）

- `loop.create_connection()` 和 `loop.create_server()` 方法已获得优化以避免当地址已被解析时调用系统的 `getaddrinfo` 函数。 （由 A. Jesse Jiryu Davis 贡献。）

- `loop.sock_connect(sock, address)` 不再要求在其被调用之前已解析 address。 （由 A. Jesse Jiryu Davis 贡献。）

### bz2

现在 `BZ2Decompressor.decompress` 方法接受可选的 max_length 参数用来限制解压缩数据的大小上限。 （由 Nikolaus Rath 在 bpo-15955 中贡献。）

### cgi

现在 `FieldStorage` 类已支持 context manager 协议。 （由 Berker Peksag 在 bpo-20289 中贡献。）

### cmath

新增函数 `isclose()` 提供了一种测试近似相等的方式。 （由 Chris Barker 和 Tal Einat 在 bpo-24270 中贡献。）

### code

现在 `InteractiveInterpreter.showtraceback()` 方法将打印完整的回溯链，就像在交互模式解释器中一样。 （由 Claudiu Popa 在 bpo-17442 中贡献。）

### collections

现在 `OrderedDict` 类使用 C 来实现，令其可提速 4 至 100 倍。 （由 Eric Snow 在 bpo-16991 中贡献。）

`OrderedDict.items()`, `OrderedDict.keys()`, `OrderedDict.values()` 等视图现在支持 `reversed()` 迭代。 （由 Serhiy Storchaka 在 bpo-19505 中贡献。）

`deque` 类现在定义了 `index()`, `insert()` 和 `copy()`，并且支持 `+` 和 `*` 运算符。 这允许 deque 被识别为 `MutableSequence` 并提升其替代列表的能力。 （由 Raymond Hettinger 在 bpo-23704 中贡献。）

由 `namedtuple()` 产生的文档字符串现在可以被更新:

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

（由 Berker Peksag 在 bpo-24064 中贡献。）

现在 `UserString` 类已实现 `__getnewargs__()`, `__rmod__()`, `casefold()`, `format_map()`, `isprintable()` 和 `maketrans()` 类以与对应的 `str` 方法相匹配。 （由 Joe Jevnik 在 bpo-22189 中贡献。）

### collections.abc

现在 `Sequence.index()` 方法接受 start 和 stop 参数以与对应的 `tuple`, `list` 等的方法相匹配。 （由 Devin Jeanpierre 在 bpo-23086 中贡献。）

新增 `Generator` 抽象基类。 （由 Stefan Behnel 在 bpo-24018 中贡献。）

新增 `Awaitable`, `Coroutine`, `AsyncIterator` 和 `AsyncIterable` 抽象基类。 （由 Yury Selivanov 在 bpo-24184 中贡献。）

对于更早的 Python，这些新 ABC 的向下移植版可通过一个外部的 PyPI 包 来获取。

### compileall

新增 `compileall` 选项 `-j N`，允许同时运行 N 个工作进程来执行并行的字节码编译。 `compile_dir()` 函数增加了相应的 `workers` 形参。 （由 Claudiu Popa 在 bpo-16104 中贡献。）

另一个新选项 `-r`，允许控制最大的子目录递归层级。 （由 Claudiu Popa 在 bpo-19628 中贡献。）

现在可以多次指定 `-q` 命令行选项，在此情况下，所有输出包括错误都将被抑制。 在 `compile_dir()`, `compile_file()` 和 `compile_path()` 中相应的 `quiet` 形参现在可接受一个整数值来指明输出抑制的级别。 （由 Thomas Kluyver 在 bpo-21338 中贡献。）

### concurrent.futures

现在 `Executor.map()` 方法接受一个 chunksize 参数以允许在使用 `ProcessPoolExecutor()` 设置任务批次来提升运行效率。 （由 Dan O'Reilly 在 bpo-11271 中贡献。）

现在 `ThreadPoolExecutor` 构造器中的工作线程数量是可选的。 默认值为 CPU 数量的 5 倍。 （由 Claudiu Popa 在 bpo-21527 中贡献。）

### configparser

现在 `configparser` 提供了一种方式通过在 `ConfigParser` 构造器中指定一个由转换器组成的字典，或将它们定义为 `ConfigParser` 子类中的方法来定制值的转换。 在解析器实例中定义的转换器将被它的节代理所继承。

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

新增的 `redirect_stderr()` context manager (类似于 `redirect_stdout()`) 使得工具脚本更容易处理那些将输出写入到 `sys.stderr` 并且不提供任何重定向选项的不灵活 API。

    >>> 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

现在 `writerow()` 方法可支持任意可迭代对象，而不仅是序列。 （由 Serhiy Storchaka 在 bpo-23171 中贡献。）

### curses

新增的 `update_lines_cols()` 函数可更新 `LINES` 和 `COLS` 模块变量。 这适用于检测手册页屏幕的大小变化。 （由 Arnon Yaari 在 bpo-4254 中贡献。）

### dbm

当设置旗标值为 `"n"` 时 `dumb.open` 将总是创建新的数据库。 （由 Claudiu Popa 在 bpo-18039 中贡献。）

### difflib

由 `HtmlDiff.make_file()` 生成的 HTML 文档的字符集现在可通过使用新增的 charset 仅限关键字参数来自定义。 HTML 文档的默认字符集已从 `"ISO-8859-1"` 改为 `"utf-8"`。 （由 Berker Peksag 在 bpo-2052 中贡献。）

现在 `diff_bytes()` 函数可能比较字节串的列表。 这修复了一个来自 Python 2 遗留总是。 （由 Terry J. Reedy 和 Greg Ward 在 bpo-17445 中贡献。）

### distutils

现在 `build` 和 `build_ext` 命令都接受一个 `-j` 选项以启用扩展模块的并行编译。 （由 Antoine Pitrou 在 bpo-5309 中贡献。）

现在 `distutils` 模块支持 `xz` 压缩，并可通过将 `xztar` 作为传给 `bdist --format` 的参数来启用。 （由 Serhiy Storchaka 在 bpo-16314 中贡献。）

### doctest

如果 module 不包含任何文档字符串则 `DocTestSuite()` 函数将返回一个空的 `unittest.TestSuite`，而不是引发 `ValueError`。 （由 Glenn Jones 在 bpo-15916 中贡献。）

### email

新增的策略选项 `Policy.mangle_from_` 可控制生成器是否要为电子邮件消息体中以controls whether or not lines that start with `"From "` 打头的行添加 `">"` 字符前缀。 默认 `compat32` 为 `True` 而所有其他策略均为 `False`。 （由 Milan Oberkirch 在 bpo-20098 中贡献。）

新增的 `Message.get_content_disposition()` 方法可提供对 Content-Disposition 标头规范值的便捷访问。 （由 Abhilash Raj 在 bpo-21083 中贡献。）

新增的策略选项 `EmailPolicy.utf8` 可被设为 `True` 以使用 UTF-8 字符集而不是使用已编码的字来编码电子邮件标头。 这将允许根据 RFC 6532 来格式化 `Messages` 并配合支持 RFC 6531 `SMTPUTF8` 扩展的 SMTP 服务器使用。 （由 R. David Murray 在 bpo-24211 中贡献。）

现在 `mime.text.MIMEText` 构造器可接受一个 `charset.Charset` 实例。 （由 Claude Paroz 和 Berker Peksag 在 bpo-16324 中贡献。）

### enum

`Enum` 可调用对象新增了一个形参 start 用于在只提供了 names 的情况下指定枚举值的初始数量:

    >>> Animal = enum.Enum('Animal', 'cat dog', start=10)
    >>> Animal.cat
    <Animal.cat: 10>
    >>> Animal.dog
    <Animal.dog: 11>

（由 Ethan Furman 在 bpo-21706 中贡献。）

### faulthandler

现在 `enable()`, `register()`, `dump_traceback()` 和 `dump_traceback_later()` 函数除了接受文件型对象以外也接受文件描述符。 （由 Wei Wu 在 bpo-23566 中贡献。）

### functools

现在大部分 `lru_cache()` 机制已使用 C 实现，使其速度显著提升。 （由 Matt Joiner, Alexey Kachayev 和 Serhiy Storchaka 在 bpo-14373 中贡献。）

### glob

现在 `iglob()` 和 `glob()` 函数支持通过使用 `"**"` 模式在子目录中递归搜索。 （由 Serhiy Storchaka 在 bpo-13968 中贡献。）

### gzip

现在 `GzipFile` 构造器的 mode 参数可接受 `"x"` 来请求独占式的创建。 （由 Tim Heaney 在 bpo-19222 中贡献。）

### heapq

现在 `merge()` 中的元素比较可通过在新增的可选关键字参数 key 中传入一个 key function 来进行定制，并且新增了可选关键字参数 reverse 用于反向的元素比较:

    >>> 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

新增的 `HTTPStatus` 枚举定义了一组 HTTP 状态码、英文短说明和长描述。 （由 Demian Brecht 在 bpo-21793 中贡献。）

### http.client

现在 `HTTPConnection.getresponse()` 在远程服务器连接被意外关闭时会引发 `RemoteDisconnected` 异常。 此外，如果引发了 `ConnectionError` (`RemoteDisconnected` 是其子类)，客户端套接字现在会自动关闭，并将在下次请求时重新连接:

    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

由于 idlelib 实现了 IDLE 命令行界面和编辑器且不应被其他程序导入，它将随每个发布版获得不断改进。 请参阅 `Lib/idlelib/NEWS.txt` 查看 3.4.0 以来的累积改变列表，以及未来 3.5.x 发布版将进行的改变。 此文件也可通过 IDLE Help ‣ About IDLE 对话框查看。

### imaplib

现在 `IMAP4` 类已支持 context manager 协议。 当用于 `with` 语句时，IMAP4 `LOGOUT` 命令将在代码块的末尾被自动调用。 （由 Tarek Ziadé 和 Serhiy Storchaka 在 bpo-4972 中贡献。）

现在 `imaplib` 模块已通过 `IMAP4.enable()` 方法支持 RFC 5161 (ENABLE 扩展) 和 RFC 6855 (UTF-8 支持)。 新增的 `IMAP4.utf8_enabled` 属性可跟踪 RFC 6855 支持是否被启用。 （由 Milan Oberkirch, R. David Murray 和 Maciej Szulik 在 bpo-21800 中贡献。）

现在 `imaplib` 模块会自动使用 UTF-8 自动编码非 ASCII 字符串的用户名和密码，如 RFC 所建议的那样。 （由 Milan Oberkirch 在 bpo-21800 中贡献。）

### imghdr

现在 `what()` 函数可识别 OpenEXR 格式（由 Martin Vignali 和 Claudiu Popa 在 bpo-20295 中贡献），以及 WebP 格式（由 Fabrice Aneche 和 Claudiu Popa 在 bpo-20197 中贡献。）

### importlib

`util.LazyLoader` 类允许在对启动时间敏感的应用程序中使用模块的惰性加载。 （由 Brett Cannon 在 bpo-17621 中贡献。）

现在 `abc.InspectLoader.source_to_code()` 方法属于静态方法。 这样将可更方便地通过运行 `exec(code, module.__dict__)` 基于字符串编译的代码来初始化模块。 （由 Brett Cannon 在 bpo-21156 中贡献。）

新增的 `util.module_from_spec()` 函数现在是创建新模块的首先方式。 相比直接创建 `types.ModuleType` 实例，这个新函数将基于传入的规格说明对象设置各种导入控制的属性。 （由 Brett Cannon 在 bpo-20383 中贡献。）

### inspect

现在 `Signature` 和 `Parameter` 类都是可封存和可哈希的对象。 （由 Yury Selivanov 在 bpo-20726 和 bpo-20334 中贡献。）

新增的 `BoundArguments.apply_defaults()` 方法提供了一种为缺失的参数设置默认值的方式:

    >>> 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。）

新增的类方法 `Signature.from_callable()` 使得 `Signature` 的子类化更为容易。 （由 Yury Selivanov 和 Eric Snow 在 bpo-17373 中贡献。）

现在 `signature()` 函数接受 follow_wrapped 可选关键字参数，当其设为 `False` 时，将禁用 `__wrapped__` 链接的自动跟随。 （由 Yury Selivanov 在 bpo-20691 中贡献。）

新增了一组用于检查 协程函数 和 协程对象 的函数: `iscoroutine()`, `iscoroutinefunction()`, `isawaitable()`, `getcoroutinelocals()` 和 `getcoroutinestate()`。 （由 Yury Selivanov 在 bpo-24017 和 bpo-24400 中贡献。）

现在 `stack()`, `trace()`, `getouterframes()` 和 `getinnerframes()` 函数将返回具名元组的列表。 （由 Daniel Shahaf 在 bpo-16808 中贡献。）

### io

新增 `BufferedIOBase.readinto1()` 方法，该方法会使用至少一次对下层原始流的调用 `RawIOBase.read()` 或 `RawIOBase.readinto()` 方法。 （由 Nikolaus Rath 在 bpo-20578 中贡献。）

### ipaddress

现在 `IPv4Network` 和 `IPv6Network` 类均接受一个 `(address, netmask)` 元组参数，可以根据现有地址方便地构造网络对象:

    >>> 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
    >>> addr = ipaddress.IPv4Address('127.0.0.1')
    >>> addr.reverse_pointer
    '1.0.0.127.in-addr.arpa'
    >>> addr6 = ipaddress.IPv6Address('::1')
    >>> addr6.reverse_pointer
    '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa'

（由 Leon Weber 在 bpo-20480 中贡献。）

### json

The `json.tool` command line interface now preserves the order of keys in JSON objects passed in input. The new `--sort-keys` option can be used to sort the keys alphabetically. (Contributed by Berker Peksag in bpo-21650.)

JSON decoder now raises `JSONDecodeError` instead of `ValueError` to provide better context information about the error. (Contributed by Serhiy Storchaka in bpo-19361.)

### linecache

A new `lazycache()` function can be used to capture information about a non-file-based module to permit getting its lines later via `getline()`. This avoids doing I/O until a line is actually needed, without having to carry the module globals around indefinitely. (Contributed by Robert Collins in bpo-17911.)

### locale

A new `delocalize()` function can be used to convert a string into a normalized number string, taking the `LC_NUMERIC` settings into account:

    >>> import locale
    >>> locale.setlocale(locale.LC_NUMERIC, 'de_DE.UTF-8')
    'de_DE.UTF-8'
    >>> locale.delocalize('1.234,56')
    '1234.56'
    >>> locale.setlocale(locale.LC_NUMERIC, 'en_US.UTF-8')
    'en_US.UTF-8'
    >>> locale.delocalize('1,234.56')
    '1234.56'

（由 Cédric Krier 在 bpo-13918 中贡献。）

### logging

All logging methods (`Logger` `log()`, `exception()`, `critical()`, `debug()`, etc.), now accept exception instances as an exc_info argument, in addition to boolean values and exception tuples:

    >>> import logging
    >>> try:
    ...     1/0
    ... except ZeroDivisionError as ex:
    ...     logging.error('exception', exc_info=ex)
    ERROR:root:exception

（由 Yury Selivanov 在 bpo-20537 中贡献。）

The `handlers.HTTPHandler` class now accepts an optional `ssl.SSLContext` instance to configure SSL settings used in an HTTP connection. (Contributed by Alex Gaynor in bpo-22788.)

The `handlers.QueueListener` class now takes a respect_handler_level keyword argument which, if set to `True`, will pass messages to handlers taking handler levels into account. (Contributed by Vinay Sajip.)

### lzma

The `LZMADecompressor.decompress()` method now accepts an optional max_length argument to limit the maximum size of decompressed data. (Contributed by Martin Panter in bpo-15955.)

### math

Two new constants have been added to the `math` module: `inf` and `nan`. (Contributed by Mark Dickinson in bpo-23185.)

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

A new `gcd()` function has been added. The `fractions.gcd()` function is now deprecated. (Contributed by Mark Dickinson and Serhiy Storchaka in bpo-22486.)

### multiprocessing

`sharedctypes.synchronized()` objects now support the context manager protocol. (Contributed by Charles-François Natali in bpo-21565.)

### operator

`attrgetter()`, `itemgetter()`, and `methodcaller()` objects now support pickling. (Contributed by Josh Rosenberg and Serhiy Storchaka in bpo-22955.)

New `matmul()` and `imatmul()` functions to perform matrix multiplication. (Contributed by Benjamin Peterson in bpo-21176.)

### os

The new `scandir()` function returning an iterator of `DirEntry` objects has been added. If possible, `scandir()` extracts file attributes while scanning a directory, removing the need to perform subsequent system calls to determine file type or attributes, which may significantly improve performance. (Contributed by Ben Hoyt with the help of Victor Stinner in bpo-22524.)

On Windows, a new `stat_result.st_file_attributes` attribute is now available. It corresponds to the `dwFileAttributes` member of the `BY_HANDLE_FILE_INFORMATION` structure returned by `GetFileInformationByHandle()`. (Contributed by Ben Hoyt in bpo-21719.)

The `urandom()` function now uses the `getrandom()` syscall on Linux 3.17 or newer, and `getentropy()` on OpenBSD 5.6 and newer, removing the need to use `/dev/urandom` and avoiding failures due to potential file descriptor exhaustion. (Contributed by Victor Stinner in bpo-22181.)

New `get_blocking()` and `set_blocking()` functions allow getting and setting a file descriptor's blocking mode (`O_NONBLOCK`.) (Contributed by Victor Stinner in bpo-22054.)

The `truncate()` and `ftruncate()` functions are now supported on Windows. (Contributed by Steve Dower in bpo-23668.)

There is a new `os.path.commonpath()` function returning the longest common sub-path of each passed pathname. Unlike the `os.path.commonprefix()` function, it always returns a valid path:

    >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
    '/usr/l'

    >>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
    '/usr'

（由 Rafik Draoui 和 Serhiy Storchaka 在 bpo-10395 中贡献。）

### pathlib

The new `Path.samefile()` method can be used to check whether the path points to the same file as another path, which can be either another `Path` object, or a string:

    >>> import pathlib
    >>> p1 = pathlib.Path('/etc/hosts')
    >>> p2 = pathlib.Path('/etc/../etc/hosts')
    >>> p1.samefile(p2)
    True

（由 Vajrasky Kok 和 Antoine Pitrou 在 bpo-19775 中贡献。）

The `Path.mkdir()` method now accepts a new optional exist_ok argument to match `mkdir -p` and `os.makedirs()` functionality. (Contributed by Berker Peksag in bpo-21539.)

There is a new `Path.expanduser()` method to expand `~` and `~user` prefixes. (Contributed by Serhiy Storchaka and Claudiu Popa in bpo-19776.)

A new `Path.home()` class method can be used to get a `Path` instance representing the user’s home directory. (Contributed by Victor Salgado and Mayank Tripathi in bpo-19777.)

New `Path.write_text()`, `Path.read_text()`, `Path.write_bytes()`, `Path.read_bytes()` methods to simplify read/write operations on files.

The following code snippet will create or rewrite existing file `~/spam42`:

    >>> import pathlib
    >>> p = pathlib.Path('~/spam42')
    >>> p.expanduser().write_text('ham')
    3

（由 Christopher Welborn 在 bpo-20218 中贡献。）

### pickle

Nested objects, such as unbound methods or nested classes, can now be pickled using pickle protocols older than protocol version 4. Protocol version 4 already supports these cases. (Contributed by Serhiy Storchaka in bpo-23611.)

### poplib

A new `POP3.utf8()` command enables RFC 6856 (Internationalized Email) support, if a POP server supports it. (Contributed by Milan OberKirch in bpo-21804.)

### re

References and conditional references to groups with fixed length are now allowed in lookbehind assertions:

    >>> import re
    >>> pat = re.compile(r'(a|b).(?<=\1)c')
    >>> pat.match('aac')
    <_sre.SRE_Match object; span=(0, 3), match='aac'>
    >>> pat.match('bbc')
    <_sre.SRE_Match object; span=(0, 3), match='bbc'>

（由 Serhiy Storchaka 在 bpo-9179 中贡献。）

The number of capturing groups in regular expressions is no longer limited to 100. (Contributed by Serhiy Storchaka in bpo-22437.)

The `sub()` and `subn()` functions now replace unmatched groups with empty strings instead of raising an exception. (Contributed by Serhiy Storchaka in bpo-1519638.)

The `re.error` exceptions have new attributes, `msg`, `pattern`, `pos`, `lineno`, and `colno`, that provide better context information about the error:

    >>> re.compile("""
    ...     (?x)
    ...     .++
    ... """)
    Traceback (most recent call last):
       ...
    sre_constants.error: multiple repeat at position 16 (line 3, column 7)

（由 Serhiy Storchaka 在 bpo-22578 中贡献。）

### readline

A new `append_history_file()` function can be used to append the specified number of trailing elements in history to the given file. (Contributed by Bruno Cauet in bpo-22940.)

### selectors

The new `DevpollSelector` supports efficient `/dev/poll` polling on Solaris. (Contributed by Giampaolo Rodola' in bpo-18931.)

### shutil

The `move()` function now accepts a copy_function argument, allowing, for example, the `copy()` function to be used instead of the default `copy2()` if there is a need to ignore file metadata when moving. (Contributed by Claudiu Popa in bpo-19840.)

The `make_archive()` function now supports the xztar format. (Contributed by Serhiy Storchaka in bpo-5411.)

### signal

On Windows, the `set_wakeup_fd()` function now also supports socket handles. (Contributed by Victor Stinner in bpo-22018.)

Various `SIG*` constants in the `signal` module have been converted into `Enums`. This allows meaningful names to be printed during debugging, instead of integer "magic numbers". (Contributed by Giampaolo Rodola' in bpo-21076.)

### smtpd

Both the `SMTPServer` and `SMTPChannel` classes now accept a decode_data keyword argument to determine if the `DATA` portion of the SMTP transaction is decoded using the `"utf-8"` codec or is instead provided to the `SMTPServer.process_message()` method as a byte string. The default is `True` for backward compatibility reasons, but will change to `False` in Python 3.6. If decode_data is set to `False`, the `process_message` method must be prepared to accept keyword arguments. (Contributed by Maciej Szulik in bpo-19662.)

The `SMTPServer` class now advertises the `8BITMIME` extension (RFC 6152) if decode_data has been set `True`. If the client specifies `BODY=8BITMIME` on the `MAIL` command, it is passed to `SMTPServer.process_message()` via the mail_options keyword. (Contributed by Milan Oberkirch and R. David Murray in bpo-21795.)

The `SMTPServer` class now also supports the `SMTPUTF8` extension (RFC 6531: Internationalized Email). If the client specified `SMTPUTF8 BODY=8BITMIME` on the `MAIL` command, they are passed to `SMTPServer.process_message()` via the mail_options keyword. It is the responsibility of the `process_message` method to correctly handle the `SMTPUTF8` data. (Contributed by Milan Oberkirch in bpo-21725.)

It is now possible to provide, directly or via name resolution, IPv6 addresses in the `SMTPServer` constructor, and have it successfully connect. (Contributed by Milan Oberkirch in bpo-14758.)

### smtplib

A new `SMTP.auth()` method provides a convenient way to implement custom authentication mechanisms. (Contributed by Milan Oberkirch in bpo-15014.)

The `SMTP.set_debuglevel()` method now accepts an additional debuglevel (2), which enables timestamps in debug messages. (Contributed by Gavin Chappell and Maciej Szulik in bpo-16914.)

Both the `SMTP.sendmail()` and `SMTP.send_message()` methods now support RFC 6531 (SMTPUTF8). (Contributed by Milan Oberkirch and R. David Murray in bpo-22027.)

### sndhdr

The `what()` and `whathdr()` functions now return a `namedtuple()`. (Contributed by Claudiu Popa in bpo-18615.)

### socket

Functions with timeouts now use a monotonic clock, instead of a system clock. (Contributed by Victor Stinner in bpo-22043.)

A new `socket.sendfile()` method allows sending a file over a socket by using the high-performance `os.sendfile()` function on UNIX, resulting in uploads being from 2 to 3 times faster than when using plain `socket.send()`. (Contributed by Giampaolo Rodola' in bpo-17552.)

The `socket.sendall()` method no longer resets the socket timeout every time bytes are received or sent. The socket timeout is now the maximum total duration to send all data. (Contributed by Victor Stinner in bpo-23853.)

The backlog argument of the `socket.listen()` method is now optional. By default it is set to `SOMAXCONN` or to `128`, whichever is less. (Contributed by Charles-François Natali in bpo-21455.)

### ssl

#### 内存 BIO 支持

（由 Geert Jansen 在 bpo-21965 中贡献。）

The new `SSLObject` class has been added to provide SSL protocol support for cases when the network I/O capabilities of `SSLSocket` are not necessary or are suboptimal. `SSLObject` represents an SSL protocol instance, but does not implement any network I/O methods, and instead provides a memory buffer interface. The new `MemoryBIO` class can be used to pass data between Python and an SSL protocol instance.

The memory BIO SSL support is primarily intended to be used in frameworks implementing asynchronous I/O for which `SSLSocket`'s readiness model ("select/poll") is inefficient.

A new `SSLContext.wrap_bio()` method can be used to create a new `SSLObject` instance.

#### Application-Layer Protocol Negotiation Support

（由 Benjamin Peterson 在 bpo-20188 中贡献。）

Where OpenSSL support is present, the `ssl` module now implements the Application-Layer Protocol Negotiation TLS extension as described in RFC 7301.

The new `SSLContext.set_alpn_protocols()` can be used to specify which protocols a socket should advertise during the TLS handshake.

The new `SSLSocket.selected_alpn_protocol()` returns the protocol that was selected during the TLS handshake. The `HAS_ALPN` flag indicates whether ALPN support is present.

#### Other Changes

There is a new `SSLSocket.version()` method to query the actual protocol version in use. (Contributed by Antoine Pitrou in bpo-20421.)

The `SSLSocket` class now implements a `SSLSocket.sendfile()` method. (Contributed by Giampaolo Rodola' in bpo-17552.)

The `SSLSocket.send()` method now raises either the `ssl.SSLWantReadError` or `ssl.SSLWantWriteError` exception on a non-blocking socket if the operation would block. Previously, it would return `0`. (Contributed by Nikolaus Rath in bpo-20951.)

The `cert_time_to_seconds()` function now interprets the input time as UTC and not as local time, per RFC 5280. Additionally, the return value is always an `int`. (Contributed by Akira Li in bpo-19940.)

New `SSLObject.shared_ciphers()` and `SSLSocket.shared_ciphers()` methods return the list of ciphers sent by the client during the handshake. (Contributed by Benjamin Peterson in bpo-23186.)

The `SSLSocket.do_handshake()`, `SSLSocket.read()`, `SSLSocket.shutdown()`, and `SSLSocket.write()` methods of the `SSLSocket` class no longer reset the socket timeout every time bytes are received or sent. The socket timeout is now the maximum total duration of the method. (Contributed by Victor Stinner in bpo-23853.)

The `match_hostname()` function now supports matching of IP addresses. (Contributed by Antoine Pitrou in bpo-23239.)

### sqlite3

The `Row` class now fully supports the sequence protocol, in particular `reversed()` iteration and slice indexing. (Contributed by Claudiu Popa in bpo-10203; by Lucas Sinclair, Jessica McKellar, and Serhiy Storchaka in bpo-13583.)

### subprocess

The new `run()` function has been added. It runs the specified command and returns a `CompletedProcess` object, which describes a finished process. The new API is more consistent and is the recommended approach to invoking subprocesses in Python code that does not need to maintain compatibility with earlier Python versions. (Contributed by Thomas Kluyver in bpo-23342.)

示例:

    >>> subprocess.run(["ls", "-l"])  # doesn't capture output
    CompletedProcess(args=['ls', '-l'], returncode=0)

    >>> subprocess.run("exit 1", shell=True, check=True)
    Traceback (most recent call last):
      ...
    subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

    >>> subprocess.run(["ls", "-l", "/dev/null"], stdout=subprocess.PIPE)
    CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
    stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n')

### sys

A new `set_coroutine_wrapper()` function allows setting a global hook that will be called whenever a coroutine object is created by an `async def` function. A corresponding `get_coroutine_wrapper()` can be used to obtain a currently set wrapper. Both functions are provisional, and are intended for debugging purposes only. (Contributed by Yury Selivanov in bpo-24017.)

A new `is_finalizing()` function can be used to check if the Python interpreter is shutting down. (Contributed by Antoine Pitrou in bpo-22696.)

### sysconfig

The name of the user scripts directory on Windows now includes the first two components of the Python version. (Contributed by Paul Moore in bpo-23437.)

### tarfile

The mode argument of the `open()` function now accepts `"x"` to request exclusive creation. (Contributed by Berker Peksag in bpo-21717.)

The `TarFile.extractall()` and `TarFile.extract()` methods now take a keyword argument numeric_owner. If set to `True`, the extracted files and directories will be owned by the numeric `uid` and `gid` from the tarfile. If set to `False` (the default, and the behavior in versions prior to 3.5), they will be owned by the named user and group in the tarfile. (Contributed by Michael Vogt and Eric Smith in bpo-23193.)

The `TarFile.list()` now accepts an optional members keyword argument that can be set to a subset of the list returned by `TarFile.getmembers()`. (Contributed by Serhiy Storchaka in bpo-21549.)

### threading

Both the `Lock.acquire()` and `RLock.acquire()` methods now use a monotonic clock for timeout management. (Contributed by Victor Stinner in bpo-22043.)

### time

The `monotonic()` function is now always available. (Contributed by Victor Stinner in bpo-22043.)

### timeit

A new command line option `-u` or `--unit=U` can be used to specify the time unit for the timer output. Supported options are `usec`, `msec`, or `sec`. (Contributed by Julian Gindi in bpo-18983.)

The `timeit()` function has a new globals parameter for specifying the namespace in which the code will be running. (Contributed by Ben Roberts in bpo-2527.)

### tkinter

The `tkinter._fix` module used for setting up the Tcl/Tk environment on Windows has been replaced by a private function in the `_tkinter` module which makes no permanent changes to environment variables. (Contributed by Zachary Ware in bpo-20035.)

### 回溯

New `walk_stack()` and `walk_tb()` functions to conveniently traverse frame and traceback objects. (Contributed by Robert Collins in bpo-17911.)

New lightweight classes: `TracebackException`, `StackSummary`, and `FrameSummary`. (Contributed by Robert Collins in bpo-17911.)

Both the `print_tb()` and `print_stack()` functions now support negative values for the limit argument. (Contributed by Dmitry Kazakov in bpo-22619.)

### types

A new `coroutine()` function to transform generator and `generator-like` objects into awaitables. (Contributed by Yury Selivanov in bpo-24017.)

A new type called `CoroutineType`, which is used for coroutine objects created by `async def` functions. (Contributed by Yury Selivanov in bpo-24400.)

### unicodedata

The `unicodedata` module now uses data from Unicode 8.0.0.

### unittest

The `TestLoader.loadTestsFromModule()` method now accepts a keyword-only argument pattern which is passed to `load_tests` as the third argument. Found packages are now checked for `load_tests` regardless of whether their path matches pattern, because it is impossible for a package name to match the default pattern. (Contributed by Robert Collins and Barry A. Warsaw in bpo-16662.)

Unittest discovery errors now are exposed in the `TestLoader.errors` attribute of the `TestLoader` instance. (Contributed by Robert Collins in bpo-19746.)

A new command line option `--locals` to show local variables in tracebacks. (Contributed by Robert Collins in bpo-22936.)

### unittest.mock

`Mock` 类具有以下改进：

- The class constructor has a new unsafe parameter, which causes mock objects to raise `AttributeError` on attribute names starting with `"assert"`. (Contributed by Kushal Das in bpo-21238.)

- A new `Mock.assert_not_called()` method to check if the mock object was called. (Contributed by Kushal Das in bpo-21262.)

The `MagicMock` class now supports `__truediv__()`, `__divmod__()` and `__matmul__()` operators. (Contributed by Johannes Baiter in bpo-20968, and Håkan Lövdahl in bpo-23581 and bpo-23568.)

It is no longer necessary to explicitly pass `create=True` to the `patch()` function when patching builtin names. (Contributed by Kushal Das in bpo-17660.)

### urllib

A new `request.HTTPPasswordMgrWithPriorAuth` class allows HTTP Basic Authentication credentials to be managed so as to eliminate unnecessary `401` response handling, or to unconditionally send credentials on the first request in order to communicate with servers that return a `404` response instead of a `401` if the `Authorization` header is not sent. (Contributed by Matej Cepl in bpo-19494 and Akshit Khurana in bpo-7159.)

A new quote_via argument for the `parse.urlencode()` function provides a way to control the encoding of query parts if needed. (Contributed by Samwyse and Arnon Yaari in bpo-13866.)

The `request.urlopen()` function accepts an `ssl.SSLContext` object as a context argument, which will be used for the HTTPS connection. (Contributed by Alex Gaynor in bpo-22366.)

The `parse.urljoin()` was updated to use the RFC 3986 semantics for the resolution of relative URLs, rather than RFC 1808 and RFC 2396. (Contributed by Demian Brecht and Senthil Kumaran in bpo-22118.)

### wsgiref

The headers argument of the `headers.Headers` class constructor is now optional. (Contributed by Pablo Torres Navarrete and SilentGhost in bpo-5800.)

### xmlrpc

The `client.ServerProxy` class now supports the context manager protocol. (Contributed by Claudiu Popa in bpo-20627.)

The `client.ServerProxy` constructor now accepts an optional `ssl.SSLContext` instance. (Contributed by Alex Gaynor in bpo-22960.)

### xml.sax

SAX parsers now support a character stream of the `xmlreader.InputSource` object. (Contributed by Serhiy Storchaka in bpo-2175.)

`parseString()` now accepts a `str` instance. (Contributed by Serhiy Storchaka in bpo-10590.)

### zipfile

ZIP output can now be written to unseekable streams. (Contributed by Serhiy Storchaka in bpo-23252.)

The mode argument of `ZipFile.open()` method now accepts `"x"` to request exclusive creation. (Contributed by Serhiy Storchaka in bpo-21717.)

## 其他模块级更改

Many functions in the `mmap`, `ossaudiodev`, `socket`, `ssl`, and `codecs` modules now accept writable bytes-like objects. (Contributed by Serhiy Storchaka in bpo-23001.)

## 性能优化

The `os.walk()` function has been sped up by 3 to 5 times on POSIX systems, and by 7 to 20 times on Windows. This was done using the new `os.scandir()` function, which exposes file information from the underlying `readdir` or `FindFirstFile`/`FindNextFile` system calls. (Contributed by Ben Hoyt with help from Victor Stinner in bpo-23605.)

Construction of `bytes(int)` (filled by zero bytes) is faster and uses less memory for large objects. `calloc()` is used instead of `malloc()` to allocate memory for these objects. (Contributed by Victor Stinner in bpo-21233.)

Some operations on `ipaddress` `IPv4Network` and `IPv6Network` have been massively sped up, such as `subnets()`, `supernet()`, `summarize_address_range()`, `collapse_addresses()`. The speed up can range from 3 to 15 times. (Contributed by Antoine Pitrou, Michel Albert, and Markus in bpo-21486, bpo-21487, bpo-20826, bpo-23266.)

Pickling of `ipaddress` objects was optimized to produce significantly smaller output. (Contributed by Serhiy Storchaka in bpo-23133.)

Many operations on `io.BytesIO` are now 50% to 100% faster. (Contributed by Serhiy Storchaka in bpo-15381 and David Wilson in bpo-22003.)

The `marshal.dumps()` function is now faster: 65--85% with versions 3 and 4, 20--25% with versions 0 to 2 on typical data, and up to 5 times in best cases. (Contributed by Serhiy Storchaka in bpo-20416 and bpo-23344.)

The UTF-32 encoder is now 3 to 7 times faster. (Contributed by Serhiy Storchaka in bpo-15027.)

Regular expressions are now parsed up to 10% faster. (Contributed by Serhiy Storchaka in bpo-19380.)

The `json.dumps()` function was optimized to run with `ensure_ascii=False` as fast as with `ensure_ascii=True`. (Contributed by Naoki Inada in bpo-23206.)

The `PyObject_IsInstance()` and `PyObject_IsSubclass()` functions have been sped up in the common case that the second argument has `type` as its metaclass. (Contributed Georg Brandl by in bpo-22540.)

Method caching was slightly improved, yielding up to 5% performance improvement in some benchmarks. (Contributed by Antoine Pitrou in bpo-22847.)

Objects from the `random` module now use 50% less memory on 64-bit builds. (Contributed by Serhiy Storchaka in bpo-23488.)

The `property()` getter calls are up to 25% faster. (Contributed by Joe Jevnik in bpo-23910.)

Instantiation of `fractions.Fraction` is now up to 30% faster. (Contributed by Stefan Behnel in bpo-22464.)

String methods `find()`, `rfind()`, `split()`, `partition()` and the `in` string operator are now significantly faster for searching 1-character substrings. (Contributed by Serhiy Storchaka in bpo-23573.)

## 构建和 C API 的改变

增加了 `calloc` 函数

- `PyMem_RawCalloc()`,

- `PyMem_Calloc()`,

- `PyObject_Calloc()`.

(Victor Stinner 贡献于 bpo-21233.)

新的 encoding/decoding 帮助函数:

- `Py_DecodeLocale()` (替代 `_Py_char2wchar()`),

- `Py_EncodeLocale()` (替代 `_Py_wchar2char()`).

（由 Victor Stinner 在 bpo-18395 中贡献。）

A new `PyCodec_NameReplaceErrors()` function to replace the unicode encode error with `\N{...}` escapes. (Contributed by Serhiy Storchaka in bpo-19676.)

A new `PyErr_FormatV()` function similar to `PyErr_Format()`, but accepts a `va_list` argument. (Contributed by Antoine Pitrou in bpo-18711.)

A new `PyExc_RecursionError` exception. (Contributed by Georg Brandl in bpo-19235.)

New `PyModule_FromDefAndSpec()`, `PyModule_FromDefAndSpec2()`, and `PyModule_ExecDef()` functions introduced by PEP 489 -- multi-phase extension module initialization. (Contributed by Petr Viktorin in bpo-24268.)

New `PyNumber_MatrixMultiply()` and `PyNumber_InPlaceMatrixMultiply()` functions to perform matrix multiplication. (Contributed by Benjamin Peterson in bpo-21176. See also PEP 465 for details.)

The `PyTypeObject.tp_finalize` slot is now part of the stable ABI.

Windows builds now require Microsoft Visual C++ 14.0, which is available as part of Visual Studio 2015.

Extension modules now include a platform information tag in their filename on some platforms (the tag is optional, and CPython will import extensions without it, although if the tag is present and mismatched, the extension won't be loaded):

- On Linux, extension module filenames end with `.cpython-<major><minor>m-<architecture>-<os>.pyd`:

  - `<major>` is the major number of the Python version; for Python 3.5 this is `3`.

  - `<minor>` is the minor number of the Python version; for Python 3.5 this is `5`.

  - `<architecture>` is the hardware architecture the extension module was built to run on. It's most commonly either `i386` for 32-bit Intel platforms or `x86_64` for 64-bit Intel (and AMD) platforms.

  - `<os>` is always `linux-gnu`, except for extensions built to talk to the 32-bit ABI on 64-bit platforms, in which case it is `linux-gnu32` (and `<architecture>` will be `x86_64`).

- On Windows, extension module filenames end with `<debug>.cp<major><minor>-<platform>.pyd`:

  - `<major>` is the major number of the Python version; for Python 3.5 this is `3`.

  - `<minor>` is the minor number of the Python version; for Python 3.5 this is `5`.

  - `<platform>` is the platform the extension module was built for, either `win32` for Win32, `win_amd64` for Win64, `win_ia64` for Windows Itanium 64, and `win_arm` for Windows on ARM.

  - If built in debug mode, `<debug>` will be `_d`, otherwise it will be blank.

- On OS X platforms, extension module filenames now end with `-darwin.so`.

- On all other platforms, extension module filenames are the same as they were with Python 3.4.

## 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.

### 已弃用的 Python 行为

Raising the `StopIteration` exception inside a generator will now generate a silent `PendingDeprecationWarning`, which will become a non-silent deprecation warning in Python 3.6 and will trigger a `RuntimeError` in Python 3.7. See PEP 479: Change StopIteration handling inside generators for details.

### 不支持的操作系统

Windows XP is no longer supported by Microsoft, thus, per PEP 11, CPython 3.5 is no longer officially supported on this OS.

### 已弃用的 Python 模块、函数和方法

The `formatter` module has now graduated to full deprecation and is still slated for removal in Python 3.6.

The `asyncio.async()` function is deprecated in favor of `ensure_future()`.

The `smtpd` module has in the past always decoded the DATA portion of email messages using the `utf-8` codec. This can now be controlled by the new decode_data keyword to `SMTPServer`. The default value is `True`, but this default is deprecated. Specify the decode_data keyword with an appropriate value to avoid the deprecation warning.

Directly assigning values to the `key`, `value` and `coded_value` of `http.cookies.Morsel` objects is deprecated. Use the `set()` method instead. In addition, the undocumented LegalChars parameter of `set()` is deprecated, and is now ignored.

Passing a format string as keyword argument format_string to the `format()` method of the `string.Formatter` class has been deprecated. (Contributed by Serhiy Storchaka in bpo-23671.)

The `platform.dist()` and `platform.linux_distribution()` functions are now deprecated. Linux distributions use too many different ways of describing themselves, so the functionality is left to a package. (Contributed by Vajrasky Kok and Berker Peksag in bpo-1322.)

The previously undocumented `from_function` and `from_builtin` methods of `inspect.Signature` are deprecated. Use the new `Signature.from_callable()` method instead. (Contributed by Yury Selivanov in bpo-24248.)

The `inspect.getargspec()` function is deprecated and scheduled to be removed in Python 3.6. (See bpo-20438 for details.)

The `inspect` `getfullargspec()`, `getcallargs()`, and `formatargspec()` functions are deprecated in favor of the `inspect.signature()` API. (Contributed by Yury Selivanov in bpo-20438.)

`getargvalues()` and `formatargvalues()` functions were inadvertently marked as deprecated with the release of Python 3.5.0.

Use of `re.LOCALE` flag with str patterns or `re.ASCII` is now deprecated. (Contributed by Serhiy Storchaka in bpo-22407.)

Use of unrecognized special sequences consisting of `'\'` and an ASCII letter in regular expression patterns and replacement patterns now raises a deprecation warning and will be forbidden in Python 3.6. (Contributed by Serhiy Storchaka in bpo-23622.)

The undocumented and unofficial use_load_tests default argument of the `unittest.TestLoader.loadTestsFromModule()` method now is deprecated and ignored. (Contributed by Robert Collins and Barry A. Warsaw in bpo-16662.)

## 移除

### API 与特性的移除

The following obsolete and previously deprecated APIs and features have been removed:

- The `__version__` attribute has been dropped from the email package. The email code hasn't been shipped separately from the stdlib for a long time, and the `__version__` string was not updated in the last few releases.

- The internal `Netrc` class in the `ftplib` module was deprecated in 3.4, and has now been removed. (Contributed by Matt Chaput in bpo-6623.)

- The concept of `.pyo` files has been removed.

- The JoinableQueue class in the provisional `asyncio` module was deprecated in 3.4.4 and is now removed. (Contributed by A. Jesse Jiryu Davis in bpo-23464.)

## 移植到Python 3.5

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 行为的改变

- 由于一个疏忽，之前的 Python 版本会错误地接受以下语法:

      f(1 for x in [1], *args)
      f(1 for x in [1], **kwargs)

  Python 3.5 now correctly raises a `SyntaxError`, as generator expressions must be put in parentheses if not a sole argument to a function.

### Python API 的变化

- PEP 475: System calls are now retried when interrupted by a signal instead of raising `InterruptedError` if the Python signal handler does not raise an exception.

- Before Python 3.5, a `datetime.time` object was considered to be false if it represented midnight in UTC. This behavior was considered obscure and error-prone and has been removed in Python 3.5. See bpo-13936 for full details.

- The `ssl.SSLSocket.send()` method now raises either `ssl.SSLWantReadError` or `ssl.SSLWantWriteError` on a non-blocking socket if the operation would block. Previously, it would return `0`. (Contributed by Nikolaus Rath in bpo-20951.)

- The `__name__` attribute of generators is now set from the function name, instead of being set from the code name. Use `gen.gi_code.co_name` to retrieve the code name. Generators also have a new `__qualname__` attribute, the qualified name, which is now used for the representation of a generator (`repr(gen)`). (Contributed by Victor Stinner in bpo-21205.)

- The deprecated "strict" mode and argument of `HTMLParser`, `HTMLParser.error()`, and the `HTMLParserError` exception have been removed. (Contributed by Ezio Melotti in bpo-15114.) The convert_charrefs argument of `HTMLParser` is now `True` by default. (Contributed by Berker Peksag in bpo-21047.)

- Although it is not formally part of the API, it is worth noting for porting purposes (ie: fixing tests) that error messages that were previously of the form "'sometype' does not support the buffer protocol" are now of the form "a bytes-like object is required, not 'sometype'". (Contributed by Ezio Melotti in bpo-16518.)

- If the current directory is set to a directory that no longer exists then `FileNotFoundError` will no longer be raised and instead `find_spec()` will return `None` without caching `None` in `sys.path_importer_cache`, which is different than the typical case (bpo-22834).

- HTTP status code and messages from `http.client` and `http.server` were refactored into a common `HTTPStatus` enum. The values in `http.client` and `http.server` remain available for backwards compatibility. (Contributed by Demian Brecht in bpo-21793.)

- When an import loader defines `importlib.machinery.Loader.exec_module()` it is now expected to also define `create_module()` (raises a `DeprecationWarning` now, will be an error in Python 3.6). If the loader inherits from `importlib.abc.Loader` then there is nothing to do, else simply define `create_module()` to return `None`. (Contributed by Brett Cannon in bpo-23014.)

- The `re.split()` function always ignored empty pattern matches, so the `"x*"` pattern worked the same as `"x+"`, and the `"\b"` pattern never worked. Now `re.split()` raises a warning if the pattern could match an empty string. For compatibility, use patterns that never match an empty string (e.g. `"x+"` instead of `"x*"`). Patterns that could only match an empty string (such as `"\b"`) now raise an error. (Contributed by Serhiy Storchaka in bpo-22818.)

- The `http.cookies.Morsel` dict-like interface has been made self consistent: morsel comparison now takes the `key` and `value` into account, `copy()` now results in a `Morsel` instance rather than a `dict`, and `update()` will now raise an exception if any of the keys in the update dictionary are invalid. In addition, the undocumented LegalChars parameter of `set()` is deprecated and is now ignored. (Contributed by Demian Brecht in bpo-2211.)

- PEP 488 has removed `.pyo` files from Python and introduced the optional `opt-` tag in `.pyc` file names. The `importlib.util.cache_from_source()` has gained an optimization parameter to help control the `opt-` tag. Because of this, the debug_override parameter of the function is now deprecated. `.pyo` files are also no longer supported as a file argument to the Python interpreter and thus serve no purpose when distributed on their own (i.e. sourceless code distribution). Due to the fact that the magic number for bytecode has changed in Python 3.5, all old `.pyo` files from previous versions of Python are invalid regardless of this PEP.

- The `socket` module now exports the `CAN_RAW_FD_FRAMES` constant on linux 3.6 and greater.

- The `ssl.cert_time_to_seconds()` function now interprets the input time as UTC and not as local time, per RFC 5280. Additionally, the return value is always an `int`. (Contributed by Akira Li in bpo-19940.)

- The `pygettext.py` Tool now uses the standard +NNNN format for timezones in the POT-Creation-Date header.

- The `smtplib` module now uses `sys.stderr` instead of the previous module-level `stderr` variable for debug output. If your (test) program depends on patching the module-level variable to capture the debug output, you will need to update it to capture sys.stderr instead.

- The `str.startswith()` and `str.endswith()` methods no longer return `True` when finding the empty string and the indexes are completely out of range. (Contributed by Serhiy Storchaka in bpo-24284.)

- The `inspect.getdoc()` function now returns documentation strings inherited from base classes. Documentation strings no longer need to be duplicated if the inherited documentation is appropriate. To suppress an inherited string, an empty string must be specified (or the documentation may be filled in). This change affects the output of the `pydoc` module and the `help()` function. (Contributed by Serhiy Storchaka in bpo-15582.)

- Nested `functools.partial()` calls are now flattened. If you were relying on the previous behavior, you can now either add an attribute to a `functools.partial()` object or you can create a subclass of `functools.partial()`. (Contributed by Alexander Belopolsky in bpo-7830.)

### C API 的变化

- The undocumented `format` member of the (non-public) `PyMemoryViewObject` structure has been removed. All extensions relying on the relevant parts in `memoryobject.h` must be rebuilt.

- The `PyMemAllocator` structure was renamed to `PyMemAllocatorEx` and a new `calloc` field was added.

- Removed non-documented macro `PyObject_REPR()` which leaked references. Use format character `%R` in `PyUnicode_FromFormat()`-like functions to format the `repr()` of the object. (Contributed by Serhiy Storchaka in bpo-22453.)

- Because the lack of the `__module__` attribute breaks pickling and introspection, a deprecation warning is now raised for builtin types without the `__module__` attribute. This would be an AttributeError in the future. (Contributed by Serhiy Storchaka in bpo-20204.)

- As part of the PEP 492 implementation, the `tp_reserved` slot of `PyTypeObject` was replaced with a `tp_as_async` slot. Refer to 协程对象 for new types, structures and functions.

## Python 3.5.4 的显著变化

### 新增 `make regen-all` 构建目标

为了简化交叉编译，并确保 CPython 能够可靠地编译而不需要已存在可用的 Python 版本，基于 autotools 的构建系统将不再尝试根据文件修改时间隐式地重新编译已生成的文件。

取而代之的是，新增了一个 `make regen-all` 命令以便在需要时强制重新生成这些文件（例如在基于预生成版本构建了 Python 的初始版本之后）。

还定义了其他一些更具选择性的重生成目标 —— 详情参见 Makefile.pre.in。

（由 Victor Stinner 在 bpo-23404 中贡献。）

在 3.5.4 版本加入.

### 移除了 `make touch` 构建目标

之前用于通过更新生成文件的修改时间来请求隐式的重新生成这些文件的 `make touch` 构建目标已被移除。

它已被新的 `make regen-all` 目标所替代。

（由 Victor Stinner 在 bpo-23404 中贡献。）

在 3.5.4 版本发生变更.