本文介绍了Python 2.7 的新功能。 Python 2.7 于2010年7月3日发布。
数字处理在许多方面得到了改进，包括浮点数和 Decimal 类。标准库中有一些有用的补充，例如大大增强的 unittest 模块，用于解析命令行选项的 argparse 模块，在 collections 模块中方便的 OrderedDict 和 Counter 类，以及许多其他改进。
Python 2.7计划成为2.x版本的最后一个发布版本，因此我们努力使其成为长期支持的好版本。为了帮助迁移到Python 3，我们在2.7中包含了几个来自Python 3.x系列的新特性。
本文并不试图提供新特性的完整规范说明，而是提供一个方便的概览。要了解完整的细节，请参阅Python 2.7的文档。如果你想了解有关设计和实现的具体考量，请参阅特定新特性的PEP或在https://bugs.python.org上讨论更改的问题。在可能的情况下，“What's New in Python”链接到每个更改的错误修正/补丁项。
Python 2.7 是 2.x 系列中的最后一个主版本，因为Python 维护人员已将新功能开发工作的重点转移到了 Python 3.x 系列中。这意味着，尽管 Python 2 会继续修复bug并更新，以便在新的硬件和支持操作系统版本上正确构建，但不会有新的功能发布。
然而，尽管在 Python 2.7 和 Python 3 之间有一个很大的公共子集，并且迁移到该公共子集或直接迁移到 Python 3 所涉及的许多更改可以安全地自动化完成。但是一些其他更改（特别是那些与Unicode处理相关的更改）可能需要仔细考虑，并且最好用自动化回归测试套件进行健壮性测试，以便有效地迁移。
这意味着 Python2.7 将长期保留，为尚未移植到 Python 3 的生产系统提供一个稳定且受支持的基础平台。Python 2.7系列的预期完整生命周期在 PEP 373 中有详细介绍。
长期保留 2.7 版的的一些关键后果：
如上所述，与早期的2.x版本相比，2.7版本的维护时间更长。目前，预计核心开发团队将继续支持Python 2.7（接收安全更新和其他错误修复），直到至少2020年（首次发布后10年，相比之下，通常的支持期为18--24个月）。
随着 Python 2.7 标准库的老化，有效地利用 Python 包索引（直接或通过重新分发者）对 Python 2 用户来说变得更加重要。除了各种任务的第三方包之外，可用的包还包括与 Python 2 兼容的 Python 3 标准库中的新模块和功能的后端移植，以及各种工具和库，这些工具和库可以让用户更容易迁移到 Python 3。 Python 包用户指南 提供了从 Python 包索引的下载和安装软件的指导。
虽然现在增强 Python 2 的首选方法是在Python包索引上发布新包，但这种方法不一定适用于所有情况，尤其是与网络安全相关的情况。在一些特殊情况下，如果在PyPI上发布新的或更新的包无法得到充分的处理，则可以使用Python增强建议过程来提出直接在Python 2标准库中添加新功能。任何此类添加及其添加的维护版本将在下面的 New Features Added to Python 2.7 Maintenance Releases 部分中注明。
对于希望从 Python2 迁移到 Python3 的项目，或者对于希望同时支持 Python2 和 Python3 用户的库和框架开发人员，可以使用各种工具和指南来帮助决定合适的方法并管理所涉及的一些技术细节。建议从 如何将 Python 2 代码移植到 Python 3 操作指南开始。
对于 Python 2.7，一个策略决定是默认情况下禁止只对开发人员有兴趣的警告。 现在，除非另有要求，否则将忽略 DeprecationWarning 及其子类，以防止用户看到应用程序触发的警告。 这个更改也在成为Python 3.2 的分歧点上进行了。 （在 stdlib-sig 上进行了讨论，并在 bpo-7319 中执行。）
在以前的版本中，默认情况下启用了 DeprecationWarning 消息，为 Python 开发人员提供了一个明确的指示，说明他们的代码可能在未来的 Python 主要版本中出现问题。
然而，越来越多基于 Python 的应用程序的用户并不直接参与这些应用程序的开发。 DeprecationWarning 消息与这些用户无关，这让他们担心应用能否真正正常工作，并让应用开发人员承担起回应这些担忧的负担。
显示通过使用 -Wdefault (简写: -Wd) 开关运行 Python，或者在运行 Python 之前将 PYTHONWARNINGS 环境变量设置为 "default" (或 "d")，可以重新启用 DeprecationWarning 消息。 Python 代码也可以通过调用 warnings.simplefilter('default') 重新启用它们。
unittest 模块还会在运行测试时自动重新启用弃用警告。
就像 Python2.6 集成了 Python3.0 的特性一样，2.7版也集成了 Python3.1 中的一些新特性。2.x 系列继续提供迁移到3.x系列的工具。
3.1 功能的部分列表，这些功能已反向移植到 2.7：
用于集合字面值的语法 ({1,2,3} 是一个可变集合)。
字典与集合推导式 ({i: i*2 for i in range(3)})。
单个 with 语句中使用多个上下文管理器。
一个 io 库的新版本，用 C 重写以提升性能。
PEP 372：将有序字典 添加到收藏集 所描述的有序字典类型。
PEP 378: 千位分隔符的格式说明符 所描述的新的 "," 格式说明符。
memoryview 对象。
importlib 模块的一个较小子集，described below。
在很多情况下，浮点数 x 的 repr() 更短：现在它基于最短的十进制字符串 ，保证四舍五入到 x。 与 Python 以前的版本一样，保证 float(repr(x)) 能恢复到 x。
浮点数到字符串和字符串到浮点数的转换已正确舍入。 round() 函数现在也能正确舍入。
PyCapsule 类型，用于为扩展模块提供 C API 。
PyLong_AsLongAndOverflow() C API 函数 。
其他新的 Python3 模式警告包括：
operator.isCallable() 和 operator.sequenceIncludes() 在 3.x 中不支持，现在会触发警告。
-3 开关现在会自动启用:option:!-Qwarn 开关，该开关会在使用经典整除法处理整数和长整数时发出警告。
常规 Python 字典以任意顺序遍历键/值对。 多年来，许多作者编写了替代实现，以记住键最初插入的顺序。 基于这些实现的经验，2.7 在 collections 模块中引入了一个新的 OrderedDict 类。
OrderedDict API 提供与普通字典相同的接口 ，但会根据键首次插入的时间，按一定顺序遍历键和值：：
>>> from collections import OrderedDict
>>> d = OrderedDict([('first', 1),
... ('second', 2),
... ('third', 3)])
>>> d.items()
[('first', 1), ('second', 2), ('third', 3)]
如果新条目覆盖了现有条目，则原插入位置保持不变
>>> d['second'] = 4
>>> d.items()
[('first', 1), ('second', 4), ('third', 3)]
删除条目并重新插入会将其移至末尾
>>> del d['second']
>>> d['second'] = 5
>>> d.items()
[('first', 1), ('third', 3), ('second', 5)]
popitem() 方法有一个可选 last 参数 ，默认为 True 。如果 last 为真 ，则返回并删除最近添加的密钥；如果为 false ，则选择最旧的密钥
>>> od = OrderedDict([(x,0) for x in range(20)])
>>> od.popitem()
(19, 0)
>>> od.popitem()
(18, 0)
>>> od.popitem(last=False)
(0, 0)
>>> od.popitem(last=False)
(1, 0)
比较两个有序字典会同时检查键和值，并要求插入顺序相同
>>> od1 = OrderedDict([('first', 1),
... ('second', 2),
... ('third', 3)])
>>> od2 = OrderedDict([('third', 3),
... ('first', 1),
... ('second', 2)])
>>> od1 == od2
False
>>> # Move 'third' key to the end
>>> del od2['third']; od2['third'] = 3
>>> od1 == od2
True
将 OrderedDict 与普通字典进行比较时，会忽略插入顺序，只比较键和值。
OrderedDict 是如何工作的？它维护一个键的双链路列表，在插入新键时将其添加到列表中。二级字典 将键映射到其对应的列表节点 ，因此删除时不必遍历整个链接列表，从而保持 O(1)。
现在，标准库支持在多个模块 中使用有序字典。
ConfigParser 模块默认使用它们，这意味着现在可以按照原来的顺序读取、修改和写回配置文件。
The _asdict() method for
collections.namedtuple() now returns an ordered dictionary with the
values appearing in the same order as the underlying tuple indices.
json 模块的 JSONDecoder 类构造器扩展了一个 object_pairs_hook 形参 ，允许解码器构建 OrderedDict 实例。此外，还添加了对第三方工具的支持，如 PyYAML 。
参见
为了使程序输出更易读，可以在大数字上添加分隔符，将其显示为 18,446,744,073,709,551,616 而不是 18446744073709551616。
完全通用的解决方案是 locale 模块 ，它可以使用不同的分隔符（北美为","，欧洲为"."）和不同的分组大小，但 locale 使用起来比较复杂，而且不适合多线程应用程序，因为不同的线程会为不同的本地生成输出。
因此，在 str.format() 方法使用的迷你语言中添加了一个简单的逗号分组机制。 在格式化浮点数时，只需在宽度和精度之间加上逗号
>>> '{:20,.2f}'.format(18446744073709551616.0)
'18,446,744,073,709,551,616.00'
格式化整数时，在宽度后面加上逗号：
>>> '{:20,d}'.format(18446744073709551616)
'18,446,744,073,709,551,616'
这种机制完全没有适应性；逗号总是用作分隔符，分组总是以三位数为一组。 逗号格式机制不如 locale 模块通用，但使用起来更方便。
参见
用于解析命令-line参数的 argparse 模块是作为 optparse 模块更强大的替代功能而添加的。
这意味着 Python 现在支持三个不同的用来解析命令行参数的模块: getopt, optparse 和 argparse。 getopt 模块非常接近 C 库的 getopt() 函数，因此它在你编写最终要用 C 来重新编写的 Python 原型代码时很有用处。 optparse 已经变得冗余，但并没有移除它的计划因为许多脚本仍然在使用它，并且也没有自动化更新这些脚本的方式。 （让 argparse API 与 optparse 的接口保持一致的提议曾被讨论但因过于繁琐和困难而被拒绝。）
简而言之，如果你是在编写新脚本并且不需要担心与 Python 较早版本的兼容性，请使用 argparse 而不是 optparse。
以下是为示例代码:
import argparse
parser = argparse.ArgumentParser(description='Command-line example.')
# Add optional switches
parser.add_argument('-v', action='store_true', dest='is_verbose',
help='produce verbose output')
parser.add_argument('-o', action='store', dest='output',
metavar='FILE',
help='direct output to FILE instead of stdout')
parser.add_argument('-C', action='store', type=int, dest='context',
metavar='NUM', default=0,
help='display NUM lines of added context')
# Allow any number of additional arguments.
parser.add_argument(nargs='*', action='store', dest='inputs',
help='input filenames (default is stdin)')
args = parser.parse_args()
print args.__dict__
除非你覆盖它，否则会自动添加 -h 和 --help 开关，并产生格式化良好的输出:
-> ./python.exe argparse-example.py --help
usage: argparse-example.py [-h] [-v] [-o FILE] [-C NUM] [inputs [inputs ...]]
Command-line example.
positional arguments:
inputs input filenames (default is stdin)
optional arguments:
-h, --help show this help message and exit
-v produce verbose output
-o FILE direct output to FILE instead of stdout
-C NUM display NUM lines of added context
与 optparse 一样，命令行开关和参数将返回为一个具有通过 dest 形参所指定的属性的对象:
-> ./python.exe argparse-example.py -v
{'output': None,
'is_verbose': True,
'context': 0,
'inputs': []}
-> ./python.exe argparse-example.py -v -o /tmp/output -C 4 file1 file2
{'output': '/tmp/output',
'is_verbose': True,
'context': 4,
'inputs': ['file1', 'file2']}
argparse has much fancier validation than optparse; you
can specify an exact number of arguments as an integer, 0 or more
arguments by passing '*', 1 or more by passing '+', or an
optional argument with '?'. A top-level parser can contain
sub-parsers to define subcommands that have different sets of
switches, as in svn commit, svn checkout, etc. You can
specify an argument's type as FileType, which will
automatically open files for you and understands that '-' means
standard input or output.
参见
argparse 文档optparse 的代码。The logging module is very flexible; applications can define
a tree of logging subsystems, and each logger in this tree can filter
out certain messages, format them differently, and direct messages to
a varying number of handlers.
All this flexibility can require a lot of configuration. You can
write Python statements to create objects and set their properties,
but a complex set-up requires verbose but boring code.
logging also supports a fileConfig()
function that parses a file, but the file format doesn't support
configuring filters, and it's messier to generate programmatically.
Python 2.7 adds a dictConfig() function that
uses a dictionary to configure logging. There are many ways to
produce a dictionary from different sources: construct one with code;
parse a file containing JSON; or use a YAML parsing library if one is
installed. For more information see 配置函数.
The following example configures two loggers, the root logger and a
logger named "network". Messages sent to the root logger will be
sent to the system log using the syslog protocol, and messages
to the "network" logger will be written to a network.log file
that will be rotated once the log reaches 1MB.
import logging
import logging.config
configdict = {
'version': 1, # Configuration schema in use; must be 1 for now
'formatters': {
'standard': {
'format': ('%(asctime)s %(name)-15s '
'%(levelname)-8s %(message)s')}},
'handlers': {'netlog': {'backupCount': 10,
'class': 'logging.handlers.RotatingFileHandler',
'filename': '/logs/network.log',
'formatter': 'standard',
'level': 'INFO',
'maxBytes': 1000000},
'syslog': {'class': 'logging.handlers.SysLogHandler',
'formatter': 'standard',
'level': 'ERROR'}},
# Specify all the subordinate loggers
'loggers': {
'network': {
'handlers': ['netlog']
}
},
# Specify properties of the root logger
'root': {
'handlers': ['syslog']
},
}
# Set up configuration
logging.config.dictConfig(configdict)
# As an example, log two error messages
logger = logging.getLogger('/')
logger.error('Database not found')
netlogger = logging.getLogger('network')
netlogger.error('Connection failed')
Three smaller enhancements to the logging module, all
implemented by Vinay Sajip, are:
The SysLogHandler class now supports
syslogging over TCP. The constructor has a socktype parameter
giving the type of socket to use, either socket.SOCK_DGRAM
for UDP or socket.SOCK_STREAM for TCP. The default
protocol remains UDP.
Logger instances gained a getChild()
method that retrieves a descendant logger using a relative path.
For example, once you retrieve a logger by doing log = getLogger('app'),
calling log.getChild('network.listen') is equivalent to
getLogger('app.network.listen').
The LoggerAdapter class gained an
isEnabledFor() method that takes a
level and returns whether the underlying logger would
process a message of that level of importance.
参见
字典方法 keys(), values(), and items() 在 Python 3.x 有所不同。 它们将返回名为 view 的对象而不是完整的列表。
在 Python 2.7 中不可能改变 keys(), values() 和 items() 的返回值因为那会破坏大量已有代码。 作为替代 3.x 版本是以新名称 viewkeys(), viewvalues() 和 viewitems() 添加的。
>>> d = dict((i*10, chr(65+i)) for i in range(26))
>>> d
{0: 'A', 130: 'N', 10: 'B', 140: 'O', 20: ..., 250: 'Z'}
>>> d.viewkeys()
dict_keys([0, 130, 10, 140, 20, 150, 30, ..., 250])
视图可以被迭代，但键和条目视图的行为也很像是集合。 & 运算符执行交集运算，| 执行并集运算:
>>> d1 = dict((i*10, chr(65+i)) for i in range(26))
>>> d2 = dict((i**.5, i) for i in range(1000))
>>> d1.viewkeys() & d2.viewkeys()
set([0.0, 10.0, 20.0, 30.0])
>>> d1.viewkeys() | range(0, 30)
set([0, 1, 130, 3, 4, 5, 6, ..., 120, 250])
视图会追踪字典及字典被修改时的内容变化:
>>> vk = d.viewkeys()
>>> vk
dict_keys([0, 130, 10, ..., 250])
>>> d[260] = '&'
>>> vk
dict_keys([0, 130, 260, 10, ..., 250])
但是，请注意在对视图进行迭代时你是不能添加或移除键的:
>>> for k in vk:
... d[k*2] = k
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: dictionary changed size during iteration
You can use the view methods in Python 2.x code, and the 2to3
converter will change them to the standard keys(),
values(), and items() methods.
参见
memoryview 对象提供与 bytes 类型的接口相匹配的另一个对象的内存内容的视图。
>>> import string
>>> m = memoryview(string.letters)
>>> m
<memory at 0x37f850>
>>> len(m) # Returns length of underlying object
52
>>> m[0], m[25], m[26] # Indexing returns one byte
('a', 'z', 'A')
>>> m2 = m[0:26] # Slicing returns another memoryview
>>> m2
<memory at 0x37f080>
视图的内容可被转换为一个字节串或整数列表：
>>> m2.tobytes()
'abcdefghijklmnopqrstuvwxyz'
>>> m2.tolist()
[97, 98, 99, 100, 101, 102, 103, ... 121, 122]
>>>
memoryview 对象允许对属于可变对象的下层对象进行修改。
>>> m2[0] = 75
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot modify read-only memory
>>> b = bytearray(string.letters) # Creating a mutable object
>>> b
bytearray(b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
>>> mb = memoryview(b)
>>> mb[0] = '*' # Assign to view, changing the bytearray.
>>> b[0:5] # The bytearray has been changed.
bytearray(b'*bcde')
>>>
参见
对Python 语言核心进行的小改动：
已从 Python 3.x 向下移植了集合字面值语法。 使用花括号来标记可变集合的内容；集合与字典的区别在于它不包含冒号及映射的值。 {} 仍然表示空字典；请使用 set() 来表示空集合。
>>> {1, 2, 3, 4, 5}
set([1, 2, 3, 4, 5])
>>> set() # empty set
set([])
>>> {} # empty dict
{}
由 Alexandre Vassalotti 向下移植; bpo-2335。
字典与集合推导式是另一个从 3.x 向下移植的特性，对列表/生成器推导式进行一般化以针对集合与字典使用字面值语法。
>>> {x: x*x for x in range(6)}
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
>>> {('a'*x) for x in range(6)}
set(['', 'a', 'aa', 'aaa', 'aaaa', 'aaaaa'])
由 Alexandre Vassalotti 向下移植; bpo-2333。
现在 with 语句可以在一个语句中使用多个上下文管理器。 上下文管理器将按从左到右的顺序处理并且每个都会被视为开始一个新的 with 语句。 这意味着:
with A() as a, B() as b:
... suite of statements ...
相当于:
with A() as a:
with B() as b:
... suite of statements ...
contextlib.nested() 函数提供了非常类似的功能，因此它不再必要并已被弃用。
(Proposed in https://codereview.appspot.com/53094; implemented by Georg Brandl.)
Conversions between floating-point numbers and strings are
now correctly rounded on most platforms. These conversions occur
in many different places: str() on
floats and complex numbers; the float and complex
constructors;
numeric formatting; serializing and
deserializing floats and complex numbers using the
marshal, pickle
and json modules;
parsing of float and imaginary literals in Python code;
and Decimal-to-float conversion.
Related to this, the repr() of a floating-point number x
now returns a result based on the shortest decimal string that's
guaranteed to round back to x under correct rounding (with
round-half-to-even rounding mode). Previously it gave a string
based on rounding x to 17 decimal digits.
The rounding library responsible for this improvement works on
Windows and on Unix platforms using the gcc, icc, or suncc
compilers. There may be a small number of platforms where correct
operation of this code cannot be guaranteed, so the code is not
used on such systems. You can find out which code is being used
by checking sys.float_repr_style, which will be short
if the new code is in use and legacy if it isn't.
Implemented by Eric Smith and Mark Dickinson, using David Gay's
dtoa.c library; bpo-7117.
Conversions from long integers and regular integers to floating point now round differently, returning the floating-point number closest to the number. This doesn't matter for small integers that can be converted exactly, but for large numbers that will unavoidably lose precision, Python 2.7 now approximates more closely. For example, Python 2.6 computed the following:
>>> n = 295147905179352891391
>>> float(n)
2.9514790517935283e+20
>>> n - long(float(n))
65535L
Python 2.7's floating-point result is larger, but much closer to the true value:
>>> n = 295147905179352891391
>>> float(n)
2.9514790517935289e+20
>>> n - long(float(n))
-1L
(Implemented by Mark Dickinson; bpo-3166.)
Integer division is also more accurate in its rounding behaviours. (Also implemented by Mark Dickinson; bpo-1811.)
Implicit coercion for complex numbers has been removed; the interpreter
will no longer ever attempt to call a __coerce__() method on complex
objects. (Removed by Meador Inge and Mark Dickinson; bpo-5211.)
The str.format() method now supports automatic numbering of the replacement
fields. This makes using str.format() more closely resemble using
%s formatting:
>>> '{}:{}:{}'.format(2009, 04, 'Sunday')
'2009:4:Sunday'
>>> '{}:{}:{day}'.format(2009, 4, day='Sunday')
'2009:4:Sunday'
The auto-numbering takes the fields from left to right, so the first {...}
specifier will use the first argument to str.format(), the next
specifier will use the next argument, and so on. You can't mix auto-numbering
and explicit numbering -- either number all of your specifier fields or none
of them -- but you can mix auto-numbering and named fields, as in the second
example above. (Contributed by Eric Smith; bpo-5237.)
Complex numbers now correctly support usage with format(),
and default to being right-aligned.
Specifying a precision or comma-separation applies to both the real
and imaginary parts of the number, but a specified field width and
alignment is applied to the whole of the resulting 1.5+3j
output. (Contributed by Eric Smith; bpo-1588 and bpo-7988.)
The 'F' format code now always formats its output using uppercase characters, so it will now produce 'INF' and 'NAN'. (Contributed by Eric Smith; bpo-3382.)
A low-level change: the object.__format__() method now triggers
a PendingDeprecationWarning if it's passed a format string,
because the __format__() method for object converts
the object to a string representation and formats that. Previously
the method silently applied the format string to the string
representation, but that could hide mistakes in Python code. If
you're supplying formatting information such as an alignment or
precision, presumably you're expecting the formatting to be applied
in some object-specific way. (Fixed by Eric Smith; bpo-7994.)
The int() and long() types gained a bit_length
method that returns the number of bits necessary to represent
its argument in binary:
>>> n = 37
>>> bin(n)
'0b100101'
>>> n.bit_length()
6
>>> n = 2**123-1
>>> n.bit_length()
123
>>> (n+1).bit_length()
124
(Contributed by Fredrik Johansson and Victor Stinner; bpo-3439.)
The import statement will no longer try an absolute import
if a relative import (e.g. from .os import sep) fails. This
fixes a bug, but could possibly break certain import
statements that were only working by accident. (Fixed by Meador Inge;
bpo-7902.)
It's now possible for a subclass of the built-in unicode type
to override the __unicode__() method. (Implemented by
Victor Stinner; bpo-1583863.)
The bytearray type's translate() method now accepts
None as its first argument. (Fixed by Georg Brandl;
bpo-4759.)
When using @classmethod and
@staticmethod to wrap
methods as class or static methods, the wrapper object now
exposes the wrapped function as their __func__
attribute.
(Contributed by Amaury Forgeot d'Arc, after a suggestion by
George Sakkis; bpo-5982.)
When a restricted set of attributes were set using __slots__,
deleting an unset attribute would not raise AttributeError
as you would expect. Fixed by Benjamin Peterson; bpo-7604.)
Two new encodings are now supported: "cp720", used primarily for Arabic text; and "cp858", a variant of CP 850 that adds the euro symbol. (CP720 contributed by Alexander Belchenko and Amaury Forgeot d'Arc in bpo-1616979; CP858 contributed by Tim Hatch in bpo-8016.)
The file object will now set the filename attribute
on the IOError exception when trying to open a directory
on POSIX platforms (noted by Jan Kaliszewski; bpo-4764), and
now explicitly checks for and forbids writing to read-only file objects
instead of trusting the C library to catch and report the error
(fixed by Stefan Krah; bpo-5677).
The Python tokenizer now translates line endings itself, so the
compile() built-in function now accepts code using any
line-ending convention. Additionally, it no longer requires that the
code end in a newline.
Extra parentheses in function definitions are illegal in Python 3.x,
meaning that you get a syntax error from def f((x)): pass. In
Python3-warning mode, Python 2.7 will now warn about this odd usage.
(Noted by James Lingard; bpo-7362.)
It's now possible to create weak references to old-style class objects. New-style classes were always weak-referenceable. (Fixed by Antoine Pitrou; bpo-8268.)
When a module object is garbage-collected, the module's dictionary is now only cleared if no one else is holding a reference to the dictionary (bpo-7140).
A new environment variable, PYTHONWARNINGS,
allows controlling warnings. It should be set to a string
containing warning settings, equivalent to those
used with the -W switch, separated by commas.
(Contributed by Brian Curtin; bpo-7301.)
For example, the following setting will print warnings every time
they occur, but turn warnings from the Cookie module into an
error. (The exact syntax for setting an environment variable varies
across operating systems and shells.)
export PYTHONWARNINGS=all,error:::Cookie:0
Several performance enhancements have been added:
A new opcode was added to perform the initial setup for
with statements, looking up the __enter__() and
__exit__() methods. (Contributed by Benjamin Peterson.)
The garbage collector now performs better for one common usage pattern: when many objects are being allocated without deallocating any of them. This would previously take quadratic time for garbage collection, but now the number of full garbage collections is reduced as the number of objects on the heap grows. The new logic only performs a full garbage collection pass when the middle generation has been collected 10 times and when the number of survivor objects from the middle generation exceeds 10% of the number of objects in the oldest generation. (Suggested by Martin von Löwis and implemented by Antoine Pitrou; bpo-4074.)
The garbage collector tries to avoid tracking simple containers which can't be part of a cycle. In Python 2.7, this is now true for tuples and dicts containing atomic types (such as ints, strings, etc.). Transitively, a dict containing tuples of atomic types won't be tracked either. This helps reduce the cost of each garbage collection by decreasing the number of objects to be considered and traversed by the collector. (Contributed by Antoine Pitrou; bpo-4688.)
Long integers are now stored internally either in base 2**15 or in base
2**30, the base being determined at build time. Previously, they
were always stored in base 2**15. Using base 2**30 gives
significant performance improvements on 64-bit machines, but
benchmark results on 32-bit machines have been mixed. Therefore,
the default is to use base 2**30 on 64-bit machines and base 2**15
on 32-bit machines; on Unix, there's a new configure option
--enable-big-digits that can be used to override this default.
Apart from the performance improvements this change should be
invisible to end users, with one exception: for testing and
debugging purposes there's a new structseq sys.long_info that
provides information about the internal format, giving the number of
bits per digit and the size in bytes of the C type used to store
each digit:
>>> import sys
>>> sys.long_info
sys.long_info(bits_per_digit=30, sizeof_digit=4)
（由 Mark Dickinson在 bpo-4258 贡献）
Another set of changes made long objects a few bytes smaller: 2 bytes smaller on 32-bit systems and 6 bytes on 64-bit. (Contributed by Mark Dickinson; bpo-5260.)
The division algorithm for long integers has been made faster by tightening the inner loop, doing shifts instead of multiplications, and fixing an unnecessary extra iteration. Various benchmarks show speedups of between 50% and 150% for long integer divisions and modulo operations. (Contributed by Mark Dickinson; bpo-5512.) Bitwise operations are also significantly faster (initial patch by Gregory Smith; bpo-1087418).
The implementation of % checks for the left-side operand being
a Python string and special-cases it; this results in a 1--3%
performance increase for applications that frequently use %
with strings, such as templating libraries.
(Implemented by Collin Winter; bpo-5176.)
List comprehensions with an if condition are compiled into
faster bytecode. (Patch by Antoine Pitrou, back-ported to 2.7
by Jeffrey Yasskin; bpo-4715.)
Converting an integer or long integer to a decimal string was made faster by special-casing base 10 instead of using a generalized conversion function that supports arbitrary bases. (Patch by Gawain Bolton; bpo-6713.)
The split(), replace(), rindex(),
rpartition(), and rsplit() methods of string-like types
(strings, Unicode strings, and bytearray objects) now use a
fast reverse-search algorithm instead of a character-by-character
scan. This is sometimes faster by a factor of 10. (Added by
Florent Xicluna; bpo-7462 and bpo-7622.)
The pickle and cPickle modules now automatically
intern the strings used for attribute names, reducing memory usage
of the objects resulting from unpickling. (Contributed by Jake
McGuire; bpo-5084.)
The cPickle module now special-cases dictionaries,
nearly halving the time required to pickle them.
(Contributed by Collin Winter; bpo-5670.)
As in every release, Python's standard library received a number of
enhancements and bug fixes. Here's a partial list of the most notable
changes, sorted alphabetically by module name. Consult the
Misc/NEWS file in the source tree for a more complete list of
changes, or look through the Subversion logs for all the details.
The bdb module's base debugging class Bdb
gained a feature for skipping modules. The constructor
now takes an iterable containing glob-style patterns such as
django.*; the debugger will not step into stack frames
from a module that matches one of these patterns.
(Contributed by Maru Newby after a suggestion by
Senthil Kumaran; bpo-5142.)
The binascii module now supports the buffer API, so it can be
used with memoryview instances and other similar buffer objects.
(Backported from 3.x by Florent Xicluna; bpo-7703.)
Updated module: the bsddb module has been updated from 4.7.2devel9
to version 4.8.4 of
the pybsddb package.
The new version features better Python 3.x compatibility, various bug fixes,
and adds several new BerkeleyDB flags and methods.
(Updated by Jesús Cea Avión; bpo-8156. The pybsddb
changelog can be read at https://hg.jcea.es/pybsddb/file/tip/ChangeLog.)
The bz2 module's BZ2File now supports the context
management protocol, so you can write with bz2.BZ2File(...) as f:.
(Contributed by Hagen Fürstenau; bpo-3860.)
New class: the Counter class in the collections
module is useful for tallying data. Counter instances
behave mostly like dictionaries but return zero for missing keys instead of
raising a KeyError:
>>> from collections import Counter
>>> c = Counter()
>>> for letter in 'here is a sample of english text':
... c[letter] += 1
...
>>> c
Counter({' ': 6, 'e': 5, 's': 3, 'a': 2, 'i': 2, 'h': 2,
'l': 2, 't': 2, 'g': 1, 'f': 1, 'm': 1, 'o': 1, 'n': 1,
'p': 1, 'r': 1, 'x': 1})
>>> c['e']
5
>>> c['z']
0
There are three additional Counter methods.
most_common() returns the N most common
elements and their counts. elements()
returns an iterator over the contained elements, repeating each
element as many times as its count.
subtract() takes an iterable and
subtracts one for each element instead of adding; if the argument is
a dictionary or another Counter, the counts are
subtracted.
>>> c.most_common(5)
[(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)]
>>> c.elements() ->
'a', 'a', ' ', ' ', ' ', ' ', ' ', ' ',
'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i',
'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's',
's', 's', 'r', 't', 't', 'x'
>>> c['e']
5
>>> c.subtract('very heavy on the letter e')
>>> c['e'] # Count is now lower
-1
Contributed by Raymond Hettinger; bpo-1696199.
New class: OrderedDict is described in the earlier
section PEP 372：将有序字典 添加到收藏集.
New method: The deque data type now has a
count() method that returns the number of
contained elements equal to the supplied argument x, and a
reverse() method that reverses the elements
of the deque in-place. deque also exposes its maximum
length as the read-only maxlen attribute.
(Both features added by Raymond Hettinger.)
The namedtuple class now has an optional rename parameter.
If rename is true, field names that are invalid because they've
been repeated or aren't legal Python identifiers will be
renamed to legal names that are derived from the field's
position within the list of fields:
>>> from collections import namedtuple
>>> T = namedtuple('T', ['field1', '$illegal', 'for', 'field2'], rename=True)
>>> T._fields
('field1', '_1', '_2', 'field2')
(Added by Raymond Hettinger; bpo-1818.)
Finally, the Mapping abstract base class now
returns NotImplemented if a mapping is compared to
another type that isn't a Mapping.
(Fixed by Daniel Stutzbach; bpo-8729.)
Constructors for the parsing classes in the ConfigParser module now
take an allow_no_value parameter, defaulting to false; if true,
options without values will be allowed. For example:
>>> import ConfigParser, StringIO
>>> sample_config = """
... [mysqld]
... user = mysql
... pid-file = /var/run/mysqld/mysqld.pid
... skip-bdb
... """
>>> config = ConfigParser.RawConfigParser(allow_no_value=True)
>>> config.readfp(StringIO.StringIO(sample_config))
>>> config.get('mysqld', 'user')
'mysql'
>>> print config.get('mysqld', 'skip-bdb')
None
>>> print config.get('mysqld', 'unknown')
Traceback (most recent call last):
...
NoOptionError: No option 'unknown' in section: 'mysqld'
(Contributed by Mats Kindahl; bpo-7005.)
Deprecated function: contextlib.nested(), which allows
handling more than one context manager with a single with
statement, has been deprecated, because the with statement
now supports multiple context managers.
The cookielib module now ignores cookies that have an invalid
version field, one that doesn't contain an integer value. (Fixed by
John J. Lee; bpo-3924.)
The copy module's deepcopy() function will now
correctly copy bound instance methods. (Implemented by
Robert Collins; bpo-1515.)
The ctypes module now always converts None to a C NULL
pointer for arguments declared as pointers. (Changed by Thomas
Heller; bpo-4606.) The underlying libffi library has been updated to version
3.0.9, containing various fixes for different platforms. (Updated
by Matthias Klose; bpo-8142.)
New method: the datetime module's timedelta class
gained a total_seconds() method that returns the
number of seconds in the duration. (Contributed by Brian Quinlan; bpo-5788.)
New method: the Decimal class gained a
from_float() class method that performs an exact
conversion of a floating-point number to a Decimal.
This exact conversion strives for the
closest decimal approximation to the floating-point representation's value;
the resulting decimal value will therefore still include the inaccuracy,
if any.
For example, Decimal.from_float(0.1) returns
Decimal('0.1000000000000000055511151231257827021181583404541015625').
(Implemented by Raymond Hettinger; bpo-4796.)
Comparing instances of Decimal with floating-point
numbers now produces sensible results based on the numeric values
of the operands. Previously such comparisons would fall back to
Python's default rules for comparing objects, which produced arbitrary
results based on their type. Note that you still cannot combine
Decimal and floating point in other operations such as addition,
since you should be explicitly choosing how to convert between float and
Decimal. (Fixed by Mark Dickinson; bpo-2531.)
The constructor for Decimal now accepts
floating-point numbers (added by Raymond Hettinger; bpo-8257)
and non-European Unicode characters such as Arabic-Indic digits
(contributed by Mark Dickinson; bpo-6595).
Most of the methods of the Context class now accept integers
as well as Decimal instances; the only exceptions are the
canonical() and is_canonical()
methods. (Patch by Juan José Conti; bpo-7633.)
When using Decimal instances with a string's
format() method, the default alignment was previously
left-alignment. This has been changed to right-alignment, which is
more sensible for numeric types. (Changed by Mark Dickinson; bpo-6857.)
Comparisons involving a signaling NaN value (or sNAN) now signal
InvalidOperation instead of silently returning a true or
false value depending on the comparison operator. Quiet NaN values
(or NaN) are now hashable. (Fixed by Mark Dickinson;
bpo-7279.)
The difflib module now produces output that is more
compatible with modern diff/patch tools
through one small change, using a tab character instead of spaces as
a separator in the header giving the filename. (Fixed by Anatoly
Techtonik; bpo-7585.)
The Distutils sdist command now always regenerates the
MANIFEST file, since even if the MANIFEST.in or
setup.py files haven't been modified, the user might have
created some new files that should be included.
(Fixed by Tarek Ziadé; bpo-8688.)
The doctest module's IGNORE_EXCEPTION_DETAIL flag
will now ignore the name of the module containing the exception
being tested. (Patch by Lennart Regebro; bpo-7490.)
The email module's Message class will
now accept a Unicode-valued payload, automatically converting the
payload to the encoding specified by output_charset.
(Added by R. David Murray; bpo-1368247.)
The Fraction class now accepts a single float or
Decimal instance, or two rational numbers, as
arguments to its constructor. (Implemented by Mark Dickinson;
rationals added in bpo-5812, and float/decimal in
bpo-8294.)
Ordering comparisons (<, <=, >, >=) between
fractions and complex numbers now raise a TypeError.
This fixes an oversight, making the Fraction
match the other numeric types.
New class: FTP_TLS in
the ftplib module provides secure FTP
connections using TLS encapsulation of authentication as well as
subsequent control and data transfers.
(Contributed by Giampaolo Rodola; bpo-2054.)
The storbinary() method for binary uploads can now restart
uploads thanks to an added rest parameter (patch by Pablo Mouzo;
bpo-6845.)
New class decorator: total_ordering() in the functools
module takes a class that defines an __eq__() method and one of
__lt__(), __le__(), __gt__(), or __ge__(),
and generates the missing comparison methods. Since the
__cmp__() method is being deprecated in Python 3.x,
this decorator makes it easier to define ordered classes.
(Added by Raymond Hettinger; bpo-5479.)
New function: cmp_to_key() will take an old-style comparison
function that expects two arguments and return a new callable that
can be used as the key parameter to functions such as
sorted(), min() and max(), etc. The primary
intended use is to help with making code compatible with Python 3.x.
(Added by Raymond Hettinger.)
New function: the gc module's is_tracked() returns
true if a given instance is tracked by the garbage collector, false
otherwise. (Contributed by Antoine Pitrou; bpo-4688.)
The gzip module's GzipFile now supports the context
management protocol, so you can write with gzip.GzipFile(...) as f:
(contributed by Hagen Fürstenau; bpo-3860), and it now implements
the io.BufferedIOBase ABC, so you can wrap it with
io.BufferedReader for faster processing
(contributed by Nir Aides; bpo-7471).
It's also now possible to override the modification time
recorded in a gzipped file by providing an optional timestamp to
the constructor. (Contributed by Jacques Frechet; bpo-4272.)
Files in gzip format can be padded with trailing zero bytes; the
gzip module will now consume these trailing bytes. (Fixed by
Tadek Pietraszek and Brian Curtin; bpo-2846.)
New attribute: the hashlib module now has an algorithms
attribute containing a tuple naming the supported algorithms.
In Python 2.7, hashlib.algorithms contains
('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512').
(Contributed by Carl Chenet; bpo-7418.)
The default HTTPResponse class used by the httplib module now
supports buffering, resulting in much faster reading of HTTP responses.
(Contributed by Kristján Valur Jónsson; bpo-4879.)
The HTTPConnection and HTTPSConnection classes
now support a source_address parameter, a (host, port) 2-tuple
giving the source address that will be used for the connection.
(Contributed by Eldon Ziegler; bpo-3972.)
The ihooks module now supports relative imports. Note that
ihooks is an older module for customizing imports,
superseded by the imputil module added in Python 2.0.
(Relative import support added by Neil Schemenauer.)
The imaplib module now supports IPv6 addresses.
(Contributed by Derek Morr; bpo-1655.)
New function: the inspect module's getcallargs()
takes a callable and its positional and keyword arguments,
and figures out which of the callable's parameters will receive each argument,
returning a dictionary mapping argument names to their values. For example:
>>> from inspect import getcallargs
>>> def f(a, b=1, *pos, **named):
... pass
...
>>> getcallargs(f, 1, 2, 3)
{'a': 1, 'b': 2, 'pos': (3,), 'named': {}}
>>> getcallargs(f, a=2, x=4)
{'a': 2, 'b': 1, 'pos': (), 'named': {'x': 4}}
>>> getcallargs(f)
Traceback (most recent call last):
...
TypeError: f() takes at least 1 argument (0 given)
由 Georg Sakkis 在 bpo-3135 中贡献。
Updated module: The io library has been upgraded to the version shipped with
Python 3.1. For 3.1, the I/O library was entirely rewritten in C
and is 2 to 20 times faster depending on the task being performed. The
original Python version was renamed to the _pyio module.
One minor resulting change: the io.TextIOBase class now
has an errors attribute giving the error setting
used for encoding and decoding errors (one of 'strict', 'replace',
'ignore').
The io.FileIO class now raises an OSError when passed
an invalid file descriptor. (Implemented by Benjamin Peterson;
bpo-4991.) The truncate() method now preserves the
file position; previously it would change the file position to the
end of the new file. (Fixed by Pascal Chambon; bpo-6939.)
New function: itertools.compress(data, selectors) takes two
iterators. Elements of data are returned if the corresponding
value in selectors is true:
itertools.compress('ABCDEF', [1,0,1,0,1,1]) =>
A, C, E, F
New function: itertools.combinations_with_replacement(iter, r)
returns all the possible r-length combinations of elements from the
iterable iter. Unlike combinations(), individual elements
can be repeated in the generated combinations:
itertools.combinations_with_replacement('abc', 2) =>
('a', 'a'), ('a', 'b'), ('a', 'c'),
('b', 'b'), ('b', 'c'), ('c', 'c')
Note that elements are treated as unique depending on their position in the input, not their actual values.
The itertools.count() function now has a step argument that
allows incrementing by values other than 1. count() also
now allows keyword arguments, and using non-integer values such as
floats or Decimal instances. (Implemented by Raymond
Hettinger; bpo-5032.)
itertools.combinations() and itertools.product()
previously raised ValueError for values of r larger than
the input iterable. This was deemed a specification error, so they
now return an empty iterator. (Fixed by Raymond Hettinger; bpo-4816.)
Updated module: The json module was upgraded to version 2.0.9 of the
simplejson package, which includes a C extension that makes
encoding and decoding faster.
(Contributed by Bob Ippolito; bpo-4136.)
To support the new collections.OrderedDict type, json.load()
now has an optional object_pairs_hook parameter that will be called
with any object literal that decodes to a list of pairs.
(Contributed by Raymond Hettinger; bpo-5381.)
The mailbox module's Maildir class now records the
timestamp on the directories it reads, and only re-reads them if the
modification time has subsequently changed. This improves
performance by avoiding unneeded directory scans. (Fixed by
A.M. Kuchling and Antoine Pitrou; bpo-1607951, bpo-6896.)
New functions: the math module gained
erf() and erfc() for the error function and the complementary error function,
expm1() which computes e**x - 1 with more precision than
using exp() and subtracting 1,
gamma() for the Gamma function, and
lgamma() for the natural log of the Gamma function.
(Contributed by Mark Dickinson and nirinA raseliarison; bpo-3366.)
The multiprocessing module's Manager* classes
can now be passed a callable that will be called whenever
a subprocess is started, along with a set of arguments that will be
passed to the callable.
(Contributed by lekma; bpo-5585.)
The Pool class, which controls a pool of worker processes,
now has an optional maxtasksperchild parameter. Worker processes
will perform the specified number of tasks and then exit, causing the
Pool to start a new worker. This is useful if tasks may leak
memory or other resources, or if some tasks will cause the worker to
become very large.
(Contributed by Charles Cazabon; bpo-6963.)
The nntplib module now supports IPv6 addresses.
(Contributed by Derek Morr; bpo-1664.)
New functions: the os module wraps the following POSIX system
calls: getresgid() and getresuid(), which return the
real, effective, and saved GIDs and UIDs;
setresgid() and setresuid(), which set
real, effective, and saved GIDs and UIDs to new values;
initgroups(), which initialize the group access list
for the current process. (GID/UID functions
contributed by Travis H.; bpo-6508. Support for initgroups added
by Jean-Paul Calderone; bpo-7333.)
The os.fork() function now re-initializes the import lock in
the child process; this fixes problems on Solaris when fork()
is called from a thread. (Fixed by Zsolt Cserna; bpo-7242.)
In the os.path module, the normpath() and
abspath() functions now preserve Unicode; if their input path
is a Unicode string, the return value is also a Unicode string.
(normpath() fixed by Matt Giuca in bpo-5827;
abspath() fixed by Ezio Melotti in bpo-3426.)
The pydoc module now has help for the various symbols that Python
uses. You can now do help('<<') or help('@'), for example.
(Contributed by David Laban; bpo-4739.)
The re module's split(), sub(), and subn()
now accept an optional flags argument, for consistency with the
other functions in the module. (Added by Gregory P. Smith.)
New function: run_path() in the runpy module
will execute the code at a provided path argument. path can be
the path of a Python source file (example.py), a compiled
bytecode file (example.pyc), a directory
(./package/), or a zip archive (example.zip). If a
directory or zip path is provided, it will be added to the front of
sys.path and the module __main__ will be imported. It's
expected that the directory or zip contains a __main__.py;
if it doesn't, some other __main__.py might be imported from
a location later in sys.path. This makes more of the machinery
of runpy available to scripts that want to mimic the way
Python's command line processes an explicit path name.
(Added by Nick Coghlan; bpo-6816.)
New function: in the shutil module, make_archive()
takes a filename, archive type (zip or tar-format), and a directory
path, and creates an archive containing the directory's contents.
(Added by Tarek Ziadé.)
shutil's copyfile() and copytree()
functions now raise a SpecialFileError exception when
asked to copy a named pipe. Previously the code would treat
named pipes like a regular file by opening them for reading, and
this would block indefinitely. (Fixed by Antoine Pitrou; bpo-3002.)
The signal module no longer re-installs the signal handler
unless this is truly necessary, which fixes a bug that could make it
impossible to catch the EINTR signal robustly. (Fixed by
Charles-Francois Natali; bpo-8354.)
New functions: in the site module, three new functions
return various site- and user-specific paths.
getsitepackages() returns a list containing all
global site-packages directories,
getusersitepackages() returns the path of the user's
site-packages directory, and
getuserbase() returns the value of the USER_BASE
environment variable, giving the path to a directory that can be used
to store data.
(Contributed by Tarek Ziadé; bpo-6693.)
The site module now reports exceptions occurring
when the sitecustomize module is imported, and will no longer
catch and swallow the KeyboardInterrupt exception. (Fixed by
Victor Stinner; bpo-3137.)
The create_connection() function
gained a source_address parameter, a (host, port) 2-tuple
giving the source address that will be used for the connection.
(Contributed by Eldon Ziegler; bpo-3972.)
The recv_into() and recvfrom_into()
methods will now write into objects that support the buffer API, most usefully
the bytearray and memoryview objects. (Implemented by
Antoine Pitrou; bpo-8104.)
The SocketServer module's TCPServer class now
supports socket timeouts and disabling the Nagle algorithm.
The disable_nagle_algorithm class attribute
defaults to False; if overridden to be true,
new request connections will have the TCP_NODELAY option set to
prevent buffering many small sends into a single TCP packet.
The timeout class attribute can hold
a timeout in seconds that will be applied to the request socket; if
no request is received within that time, handle_timeout()
will be called and handle_request() will return.
(Contributed by Kristján Valur Jónsson; bpo-6192 and bpo-6267.)
Updated module: the sqlite3 module has been updated to
version 2.6.0 of the pysqlite package. Version 2.6.0 includes a number of bugfixes, and adds
the ability to load SQLite extensions from shared libraries.
Call the enable_load_extension(True) method to enable extensions,
and then call load_extension() to load a particular shared library.
(Updated by Gerhard Häring.)
The ssl module's SSLSocket objects now support the
buffer API, which fixed a test suite failure (fix by Antoine Pitrou;
bpo-7133) and automatically set
OpenSSL's SSL_MODE_AUTO_RETRY, which will prevent an error
code being returned from recv() operations that trigger an SSL
renegotiation (fix by Antoine Pitrou; bpo-8222).
The wrap_socket() constructor function now takes a
ciphers argument that's a string listing the encryption algorithms
to be allowed; the format of the string is described
in the OpenSSL documentation.
(Added by Antoine Pitrou; bpo-8322.)
Another change makes the extension load all of OpenSSL's ciphers and digest algorithms so that they're all available. Some SSL certificates couldn't be verified, reporting an "unknown algorithm" error. (Reported by Beda Kosata, and fixed by Antoine Pitrou; bpo-8484.)
The version of OpenSSL being used is now available as the module
attributes ssl.OPENSSL_VERSION (a string),
ssl.OPENSSL_VERSION_INFO (a 5-tuple), and
ssl.OPENSSL_VERSION_NUMBER (an integer). (Added by Antoine
Pitrou; bpo-8321.)
The struct module will no longer silently ignore overflow
errors when a value is too large for a particular integer format
code (one of bBhHiIlLqQ); it now always raises a
struct.error exception. (Changed by Mark Dickinson;
bpo-1523.) The pack() function will also
attempt to use __index__() to convert and pack non-integers
before trying the __int__() method or reporting an error.
(Changed by Mark Dickinson; bpo-8300.)
New function: the subprocess module's
check_output() runs a command with a specified set of arguments
and returns the command's output as a string when the command runs without
error, or raises a CalledProcessError exception otherwise.
>>> subprocess.check_output(['df', '-h', '.'])
'Filesystem Size Used Avail Capacity Mounted on\n
/dev/disk0s2 52G 49G 3.0G 94% /\n'
>>> subprocess.check_output(['df', '-h', '/bogus'])
...
subprocess.CalledProcessError: Command '['df', '-h', '/bogus']' returned non-zero exit status 1
（由 Gregory P. Smith 贡献）
The subprocess module will now retry its internal system calls
on receiving an EINTR signal. (Reported by several people; final
patch by Gregory P. Smith in bpo-1068268.)
New function: is_declared_global() in the symtable module
returns true for variables that are explicitly declared to be global,
false for ones that are implicitly global.
(Contributed by Jeremy Hylton.)
The syslog module will now use the value of sys.argv[0] as the
identifier instead of the previous default value of 'python'.
(Changed by Sean Reifschneider; bpo-8451.)
The sys.version_info value is now a named tuple, with attributes
named major, minor, micro,
releaselevel, and serial. (Contributed by Ross
Light; bpo-4285.)
sys.getwindowsversion() also returns a named tuple,
with attributes named major, minor, build,
platform, service_pack, service_pack_major,
service_pack_minor, suite_mask, and
product_type. (Contributed by Brian Curtin; bpo-7766.)
The tarfile module's default error handling has changed, to
no longer suppress fatal errors. The default error level was previously 0,
which meant that errors would only result in a message being written to the
debug log, but because the debug log is not activated by default,
these errors go unnoticed. The default error level is now 1,
which raises an exception if there's an error.
(Changed by Lars Gustäbel; bpo-7357.)
tarfile now supports filtering the TarInfo
objects being added to a tar file. When you call add(),
you may supply an optional filter argument
that's a callable. The filter callable will be passed the
TarInfo for every file being added, and can modify and return it.
If the callable returns None, the file will be excluded from the
resulting archive. This is more powerful than the existing
exclude argument, which has therefore been deprecated.
(Added by Lars Gustäbel; bpo-6856.)
The TarFile class also now supports the context management protocol.
(Added by Lars Gustäbel; bpo-7232.)
The wait() method of the threading.Event class
now returns the internal flag on exit. This means the method will usually
return true because wait() is supposed to block until the
internal flag becomes true. The return value will only be false if
a timeout was provided and the operation timed out.
(Contributed by Tim Lesher; bpo-1674032.)
The Unicode database provided by the unicodedata module is
now used internally to determine which characters are numeric,
whitespace, or represent line breaks. The database also
includes information from the Unihan.txt data file (patch
by Anders Chrigström and Amaury Forgeot d'Arc; bpo-1571184)
and has been updated to version 5.2.0 (updated by
Florent Xicluna; bpo-8024).
The urlparse module's urlsplit() now handles
unknown URL schemes in a fashion compliant with RFC 3986: if the
URL is of the form "<something>://...", the text before the
:// is treated as the scheme, even if it's a made-up scheme that
the module doesn't know about. This change may break code that
worked around the old behaviour. For example, Python 2.6.4 or 2.5
will return the following:
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', '', '//host/filename?query', '', '')
Python 2.7 (and Python 2.6.5) will return:
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', 'host', '/filename?query', '', '')
(Python 2.7 actually produces slightly different output, since it returns a named tuple instead of a standard tuple.)
The urlparse module also supports IPv6 literal addresses as defined by
RFC 2732 (contributed by Senthil Kumaran; bpo-2987).
>>> urlparse.urlparse('http://[1080::8:800:200C:417A]/foo')
ParseResult(scheme='http', netloc='[1080::8:800:200C:417A]',
path='/foo', params='', query='', fragment='')
New class: the WeakSet class in the weakref
module is a set that only holds weak references to its elements; elements
will be removed once there are no references pointing to them.
(Originally implemented in Python 3.x by Raymond Hettinger, and backported
to 2.7 by Michael Foord.)
The xml.etree.ElementTree library, no longer escapes
ampersands and angle brackets when outputting an XML processing
instruction (which looks like <?xml-stylesheet href="#style1"?>)
or comment (which looks like <!-- comment -->).
(Patch by Neil Muller; bpo-2746.)
The XML-RPC client and server, provided by the xmlrpclib and
SimpleXMLRPCServer modules, have improved performance by
supporting HTTP/1.1 keep-alive and by optionally using gzip encoding
to compress the XML being exchanged. The gzip compression is
controlled by the encode_threshold attribute of
SimpleXMLRPCRequestHandler, which contains a size in bytes;
responses larger than this will be compressed.
(Contributed by Kristján Valur Jónsson; bpo-6267.)
The zipfile module's ZipFile now supports the context
management protocol, so you can write with zipfile.ZipFile(...) as f:.
(Contributed by Brian Curtin; bpo-5511.)
zipfile now also supports archiving empty directories and
extracts them correctly. (Fixed by Kuba Wieczorek; bpo-4710.)
Reading files out of an archive is faster, and interleaving
read() and
readline() now works correctly.
(Contributed by Nir Aides; bpo-7610.)
The is_zipfile() function now
accepts a file object, in addition to the path names accepted in earlier
versions. (Contributed by Gabriel Genellina; bpo-4756.)
The writestr() method now has an optional compress_type parameter
that lets you override the default compression method specified in the
ZipFile constructor. (Contributed by Ronald Oussoren;
bpo-6003.)
Python 3.1 includes the importlib package, a re-implementation
of the logic underlying Python's import statement.
importlib is useful for implementers of Python interpreters and
to users who wish to write new importers that can participate in the
import process. Python 2.7 doesn't contain the complete
importlib package, but instead has a tiny subset that contains
a single function, import_module().
import_module(name, package=None) imports a module. name is
a string containing the module or package's name. It's possible to do
relative imports by providing a string that begins with a .
character, such as ..utils.errors. For relative imports, the
package argument must be provided and is the name of the package that
will be used as the anchor for
the relative import. import_module() both inserts the imported
module into sys.modules and returns the module object.
这是一些例子:
>>> from importlib import import_module
>>> anydbm = import_module('anydbm') # Standard absolute import
>>> anydbm
<module 'anydbm' from '/p/python/Lib/anydbm.py'>
>>> # Relative import
>>> file_util = import_module('..file_util', 'distutils.command')
>>> file_util
<module 'distutils.file_util' from '/python/Lib/distutils/file_util.pyc'>
importlib was implemented by Brett Cannon and introduced in
Python 3.1.
The sysconfig module has been pulled out of the Distutils
package, becoming a new top-level module in its own right.
sysconfig provides functions for getting information about
Python's build process: compiler switches, installation paths, the
platform name, and whether Python is running from its source
directory.
该模块中的部分函数:
get_config_var() 返回来自 Python 的 Makefile 和 pyconfig.h 文件的变量。
get_config_vars() 返回一个包含所有配置变量的字典。
get_path() 返回特定模块类型的配置路径：标准库、站点专属模块、平台专属模块等等。
is_python_build() 会在你从 Python 源码树运行二进制可执行文件时返回真值，而在其他情况下返回假值。
Consult the sysconfig documentation for more details and for
a complete list of functions.
The Distutils package and sysconfig are now maintained by Tarek
Ziadé, who has also started a Distutils2 package (source repository at
https://hg.python.org/distutils2/) for developing a next-generation
version of Distutils.
Tcl/Tk 8.5 includes a set of themed widgets that re-implement basic Tk widgets but have a more customizable appearance and can therefore more closely resemble the native platform's widgets. This widget set was originally called Tile, but was renamed to Ttk (for "themed Tk") on being added to Tcl/Tck release 8.5.
To learn more, read the ttk module documentation. You may also
wish to read the Tcl/Tk manual page describing the
Ttk theme engine, available at
https://www.tcl.tk/man/tcl8.5/TkCmd/ttk\_intro.html. Some
screenshots of the Python/Ttk code in use are at
https://code.google.com/archive/p/python-ttk/wikis/Screenshots.wiki.
The tkinter.ttk module was written by Guilherme Polo and added in
bpo-2983. An alternate version called Tile.py, written by
Martin Franklin and maintained by Kevin Walzer, was proposed for
inclusion in bpo-2618, but the authors argued that Guilherme
Polo's work was more comprehensive.
The unittest module was greatly enhanced; many
new features were added. Most of these features were implemented
by Michael Foord, unless otherwise noted. The enhanced version of
the module is downloadable separately for use with Python versions 2.4 to 2.6,
packaged as the unittest2 package, from unittest2.
When used from the command line, the module can automatically discover
tests. It's not as fancy as py.test or
nose, but provides a
simple way to run tests kept within a set of package directories. For example,
the following command will search the test/ subdirectory for
any importable test files named test*.py:
python -m unittest discover -s test
Consult the unittest module documentation for more details.
(Developed in bpo-6001.)
The main() function supports some other new options:
-b or --buffer will buffer the standard output
and standard error streams during each test. If the test passes,
any resulting output will be discarded; on failure, the buffered
output will be displayed.
-c or --catch will cause the control-C interrupt
to be handled more gracefully. Instead of interrupting the test
process immediately, the currently running test will be completed
and then the partial results up to the interruption will be reported.
If you're impatient, a second press of control-C will cause an immediate
interruption.
This control-C handler tries to avoid causing problems when the code
being tested or the tests being run have defined a signal handler of
their own, by noticing that a signal handler was already set and
calling it. If this doesn't work for you, there's a
removeHandler() decorator that can be used to mark tests that
should have the control-C handling disabled.
-f or --failfast makes
test execution stop immediately when a test fails instead of
continuing to execute further tests. (Suggested by Cliff Dyer and
implemented by Michael Foord; bpo-8074.)
The progress messages now show 'x' for expected failures and 'u' for unexpected successes when run in verbose mode. (Contributed by Benjamin Peterson.)
Test cases can raise the SkipTest exception to skip a
test (bpo-1034053).
The error messages for assertEqual(),
assertTrue(), and assertFalse()
failures now provide more information. If you set the
longMessage attribute of your TestCase classes to
true, both the standard error message and any additional message you
provide will be printed for failures. (Added by Michael Foord; bpo-5663.)
The assertRaises() method now
returns a context handler when called without providing a callable
object to run. For example, you can write this:
with self.assertRaises(KeyError):
{}['foo']
(Implemented by Antoine Pitrou; bpo-4444.)
Module- and class-level setup and teardown fixtures are now supported.
Modules can contain setUpModule() and tearDownModule()
functions. Classes can have setUpClass() and
tearDownClass() methods that must be defined as class methods
(using @classmethod or equivalent). These functions and
methods are invoked when the test runner switches to a test case in a
different module or class.
The methods addCleanup() and
doCleanups() were added.
addCleanup() lets you add cleanup functions that
will be called unconditionally (after setUp() if
setUp() fails, otherwise after tearDown()). This allows
for much simpler resource allocation and deallocation during tests
(bpo-5679).
A number of new methods were added that provide more specialized
tests. Many of these methods were written by Google engineers
for use in their test suites; Gregory P. Smith, Michael Foord, and
GvR worked on merging them into Python's version of unittest.
assertIsNone() and assertIsNotNone() take one
expression and verify that the result is or is not None.
assertIs() and assertIsNot()
take two values and check whether the two values evaluate to the same object or not.
(Added by Michael Foord; bpo-2578.)
assertIsInstance() and
assertNotIsInstance() check whether
the resulting object is an instance of a particular class, or of
one of a tuple of classes. (Added by Georg Brandl; bpo-7031.)
assertGreater(), assertGreaterEqual(),
assertLess(), and assertLessEqual() compare
two quantities.
assertMultiLineEqual() compares two strings, and if they're
not equal, displays a helpful comparison that highlights the
differences in the two strings. This comparison is now used by
default when Unicode strings are compared with assertEqual().
assertRegexpMatches() and
assertNotRegexpMatches() checks whether the
first argument is a string matching or not matching the regular
expression provided as the second argument (bpo-8038).
assertRaisesRegexp() checks
whether a particular exception
is raised, and then also checks that the string representation of
the exception matches the provided regular expression.
assertIn() and assertNotIn()
tests whether first is or is not in second.
assertItemsEqual() tests whether two provided sequences
contain the same elements.
assertSetEqual() compares whether two sets are equal, and
only reports the differences between the sets in case of error.
Similarly, assertListEqual() and assertTupleEqual()
compare the specified types and explain any differences without necessarily
printing their full values; these methods are now used by default
when comparing lists and tuples using assertEqual().
More generally, assertSequenceEqual() compares two sequences
and can optionally check whether both sequences are of a
particular type.
assertDictEqual() compares two dictionaries and reports the
differences; it's now used by default when you compare two dictionaries
using assertEqual(). assertDictContainsSubset() checks whether
all of the key/value pairs in first are found in second.
assertAlmostEqual() and assertNotAlmostEqual() test
whether first and second are approximately equal. This method
can either round their difference to an optionally specified number
of places (the default is 7) and compare it to zero, or require
the difference to be smaller than a supplied delta value.
loadTestsFromName() properly honors the
suiteClass attribute of
the TestLoader. (Fixed by Mark Roddy; bpo-6866.)
A new hook lets you extend the assertEqual() method to handle
new data types. The addTypeEqualityFunc() method takes a type
object and a function. The function will be used when both of the
objects being compared are of the specified type. This function
should compare the two objects and raise an exception if they don't
match; it's a good idea for the function to provide additional
information about why the two objects aren't matching, much as the new
sequence comparison methods do.
unittest.main() now takes an optional exit argument. If
false, main() doesn't call sys.exit(), allowing
main() to be used from the interactive interpreter.
(Contributed by J. Pablo Fernández; bpo-3379.)
TestResult has new startTestRun() and
stopTestRun() methods that are called immediately before
and after a test run. (Contributed by Robert Collins; bpo-5728.)
With all these changes, the unittest.py was becoming awkwardly
large, so the module was turned into a package and the code split into
several files (by Benjamin Peterson). This doesn't affect how the
module is imported or used.
参见
The version of the ElementTree library included with Python was updated to version 1.3. Some of the new features are:
The various parsing functions now take a parser keyword argument
giving an XMLParser instance that will
be used. This makes it possible to override the file's internal encoding:
p = ET.XMLParser(encoding='utf-8')
t = ET.XML("""<root/>""", parser=p)
Errors in parsing XML now raise a ParseError exception, whose
instances have a position attribute
containing a (line, column) tuple giving the location of the problem.
ElementTree's code for converting trees to a string has been
significantly reworked, making it roughly twice as fast in many
cases. The ElementTree.write()
and Element.write() methods now have a method parameter that can be
"xml" (the default), "html", or "text". HTML mode will output empty
elements as <empty></empty> instead of <empty/>, and text
mode will skip over elements and only output the text chunks. If
you set the tag attribute of an
element to None but
leave its children in place, the element will be omitted when the
tree is written out, so you don't need to do more extensive rearrangement
to remove a single element.
Namespace handling has also been improved. All xmlns:<whatever>
declarations are now output on the root element, not scattered throughout
the resulting XML. You can set the default namespace for a tree
by setting the default_namespace attribute and can
register new prefixes with register_namespace(). In XML mode,
you can use the true/false xml_declaration parameter to suppress the
XML declaration.
New Element method:
extend() appends the items from a
sequence to the element's children. Elements themselves behave like
sequences, so it's easy to move children from one element to
another:
from xml.etree import ElementTree as ET
t = ET.XML("""<list>
<item>1</item> <item>2</item> <item>3</item>
</list>""")
new = ET.XML('<root/>')
new.extend(t)
# Outputs <root><item>1</item>...</root>
print ET.tostring(new)
New Element method:
iter() yields the children of the
element as a generator. It's also possible to write for child in elem: to loop over an element's children. The existing method
getiterator() is now deprecated, as is getchildren()
which constructs and returns a list of children.
New Element method:
itertext() yields all chunks of
text that are descendants of the element. For example:
t = ET.XML("""<list>
<item>1</item> <item>2</item> <item>3</item>
</list>""")
# Outputs ['\n ', '1', ' ', '2', ' ', '3', '\n']
print list(t.itertext())
Deprecated: using an element as a Boolean (i.e., if elem:) would
return true if the element had any children, or false if there were
no children. This behaviour is confusing -- None is false, but
so is a childless element? -- so it will now trigger a
FutureWarning. In your code, you should be explicit: write
len(elem) != 0 if you're interested in the number of children,
or elem is not None.
Fredrik Lundh develops ElementTree and produced the 1.3 version; you can read his article describing 1.3 at https://web.archive.org/web/20200703234532/http://effbot.org/zone/elementtree-13-intro.htm. Florent Xicluna updated the version included with Python, after discussions on python-dev and in bpo-6472.)
针对 Python 构建过程和 C API 的改变包括:
The latest release of the GNU Debugger, GDB 7, can be scripted
using Python.
When you begin debugging an executable program P, GDB will look for
a file named P-gdb.py and automatically read it. Dave Malcolm
contributed a python-gdb.py that adds a number of
commands useful when debugging Python itself. For example,
py-up and py-down go up or down one Python stack frame,
which usually corresponds to several C stack frames. py-print
prints the value of a Python variable, and py-bt prints the
Python stack trace. (Added as a result of bpo-8032.)
If you use the .gdbinit file provided with Python,
the "pyo" macro in the 2.7 version now works correctly when the thread being
debugged doesn't hold the GIL; the macro now acquires it before printing.
(Contributed by Victor Stinner; bpo-3632.)
Py_AddPendingCall() is now thread-safe, letting any
worker thread submit notifications to the main Python thread. This
is particularly useful for asynchronous IO operations.
(Contributed by Kristján Valur Jónsson; bpo-4293.)
New function: PyCode_NewEmpty() creates an empty code object;
only the filename, function name, and first line number are required.
This is useful for extension modules that are attempting to
construct a more useful traceback stack. Previously such
extensions needed to call PyCode_New(), which had many
more arguments. (Added by Jeffrey Yasskin.)
New function: PyErr_NewExceptionWithDoc() creates a new
exception class, just as the existing PyErr_NewException() does,
but takes an extra char * argument containing the docstring for the
new exception class. (Added by 'lekma' on the Python bug tracker;
bpo-7033.)
New function: PyFrame_GetLineNumber() takes a frame object
and returns the line number that the frame is currently executing.
Previously code would need to get the index of the bytecode
instruction currently executing, and then look up the line number
corresponding to that address. (Added by Jeffrey Yasskin.)
New functions: PyLong_AsLongAndOverflow() and
PyLong_AsLongLongAndOverflow() approximates a Python long
integer as a C long or long long.
If the number is too large to fit into
the output type, an overflow flag is set and returned to the caller.
(Contributed by Case Van Horsen; bpo-7528 and bpo-7767.)
New function: stemming from the rewrite of string-to-float conversion,
a new PyOS_string_to_double() function was added. The old
PyOS_ascii_strtod() and PyOS_ascii_atof() functions
are now deprecated.
New function: PySys_SetArgvEx() sets the value of
sys.argv and can optionally update sys.path to include the
directory containing the script named by sys.argv[0] depending
on the value of an updatepath parameter.
This function was added to close a security hole for applications
that embed Python. The old function, PySys_SetArgv(), would
always update sys.path, and sometimes it would add the current
directory. This meant that, if you ran an application embedding
Python in a directory controlled by someone else, attackers could
put a Trojan-horse module in the directory (say, a file named
os.py) that your application would then import and run.
If you maintain a C/C++ application that embeds Python, check
whether you're calling PySys_SetArgv() and carefully consider
whether the application should be using PySys_SetArgvEx()
with updatepath set to false.
Security issue reported as CVE 2008-5983; discussed in bpo-5753, and fixed by Antoine Pitrou.
New macros: the Python header files now define the following macros:
Py_ISALNUM,
Py_ISALPHA,
Py_ISDIGIT,
Py_ISLOWER,
Py_ISSPACE,
Py_ISUPPER,
Py_ISXDIGIT,
Py_TOLOWER, and Py_TOUPPER.
All of these functions are analogous to the C
standard macros for classifying characters, but ignore the current
locale setting, because in
several places Python needs to analyze characters in a
locale-independent way. (Added by Eric Smith;
bpo-5793.)
Removed function: PyEval_CallObject() is now only available
as a macro. A function version was being kept around to preserve
ABI linking compatibility, but that was in 1997; it can certainly be
deleted by now. (Removed by Antoine Pitrou; bpo-8276.)
New format codes: the PyString_FromFormat(),
PyString_FromFormatV(), and PyErr_Format() functions now
accept %lld and %llu format codes for displaying
C's long long types.
(Contributed by Mark Dickinson; bpo-7228.)
The complicated interaction between threads and process forking has
been changed. Previously, the child process created by
os.fork() might fail because the child is created with only a
single thread running, the thread performing the os.fork().
If other threads were holding a lock, such as Python's import lock,
when the fork was performed, the lock would still be marked as
"held" in the new process. But in the child process nothing would
ever release the lock, since the other threads weren't replicated,
and the child process would no longer be able to perform imports.
Python 2.7 acquires the import lock before performing an
os.fork(), and will also clean up any locks created using the
threading module. C extension modules that have internal
locks, or that call fork() themselves, will not benefit
from this clean-up.
(Fixed by Thomas Wouters; bpo-1590864.)
The Py_Finalize() function now calls the internal
threading._shutdown() function; this prevents some exceptions from
being raised when an interpreter shuts down.
(Patch by Adam Olsen; bpo-1722344.)
When using the PyMemberDef structure to define attributes
of a type, Python will no longer let you try to delete or set a
T_STRING_INPLACE attribute.
Global symbols defined by the ctypes module are now prefixed
with Py, or with _ctypes. (Implemented by Thomas
Heller; bpo-3102.)
New configure option: the --with-system-expat switch allows
building the pyexpat module to use the system Expat library.
(Contributed by Arfrever Frehtes Taifersar Arahesis; bpo-7609.)
New configure option: the
--with-valgrind option will now disable the pymalloc
allocator, which is difficult for the Valgrind memory-error detector
to analyze correctly.
Valgrind will therefore be better at detecting memory leaks and
overruns. (Contributed by James Henstridge; bpo-2422.)
New configure option: you can now supply an empty string to
--with-dbmliborder= in order to disable all of the various
DBM modules. (Added by Arfrever Frehtes Taifersar Arahesis;
bpo-6491.)
The configure script now checks for floating-point rounding bugs
on certain 32-bit Intel chips and defines a X87_DOUBLE_ROUNDING
preprocessor definition. No code currently uses this definition,
but it's available if anyone wishes to use it.
(Added by Mark Dickinson; bpo-2937.)
configure also now sets a LDCXXSHARED Makefile
variable for supporting C++ linking. (Contributed by Arfrever
Frehtes Taifersar Arahesis; bpo-1222585.)
The build process now creates the necessary files for pkg-config support. (Contributed by Clinton Roy; bpo-3585.)
The build process now supports Subversion 1.7. (Contributed by Arfrever Frehtes Taifersar Arahesis; bpo-6094.)
Python 3.1 adds a new C datatype, PyCapsule, for providing a
C API to an extension module. A capsule is essentially the holder of
a C void * pointer, and is made available as a module attribute; for
example, the socket module's API is exposed as socket.CAPI,
and unicodedata exposes ucnhash_CAPI. Other extensions
can import the module, access its dictionary to get the capsule
object, and then get the void * pointer, which will usually point
to an array of pointers to the module's various API functions.
There is an existing data type already used for this,
PyCObject, but it doesn't provide type safety. Evil code
written in pure Python could cause a segmentation fault by taking a
PyCObject from module A and somehow substituting it for the
PyCObject in module B. Capsules know their own name,
and getting the pointer requires providing the name:
void *vtable;
if (!PyCapsule_IsValid(capsule, "mymodule.CAPI") {
PyErr_SetString(PyExc_ValueError, "argument type invalid");
return NULL;
}
vtable = PyCapsule_GetPointer(capsule, "mymodule.CAPI");
You are assured that vtable points to whatever you're expecting.
If a different capsule was passed in, PyCapsule_IsValid() would
detect the mismatched name and return false. Refer to
给扩展模块提供C API for more information on using these objects.
Python 2.7 now uses capsules internally to provide various
extension-module APIs, but the PyCObject_AsVoidPtr() was
modified to handle capsules, preserving compile-time compatibility
with the PyCObject interface. Use of
PyCObject_AsVoidPtr() will signal a
PendingDeprecationWarning, which is silent by default.
Implemented in Python 3.1 and backported to 2.7 by Larry Hastings; discussed in bpo-5630.
The msvcrt module now contains some constants from
the crtassem.h header file:
CRT_ASSEMBLY_VERSION,
VC_ASSEMBLY_PUBLICKEYTOKEN,
and LIBRARIES_ASSEMBLY_NAME_PREFIX.
(Contributed by David Cournapeau; bpo-4365.)
The _winreg module for accessing the registry now implements
the CreateKeyEx() and DeleteKeyEx()
functions, extended versions of previously supported functions that
take several extra arguments. The DisableReflectionKey(),
EnableReflectionKey(), and QueryReflectionKey()
were also tested and documented.
(Implemented by Brian Curtin: bpo-7347.)
The new _beginthreadex() API is used to start threads, and
the native thread-local storage functions are now used.
(Contributed by Kristján Valur Jónsson; bpo-3582.)
The os.kill() function now works on Windows. The signal value
can be the constants CTRL_C_EVENT,
CTRL_BREAK_EVENT, or any integer. The first two constants
will send Control-C and Control-Break keystroke events to
subprocesses; any other value will use the TerminateProcess()
API. (Contributed by Miki Tebeka; bpo-1220212.)
The os.listdir() function now correctly fails
for an empty path. (Fixed by Hirokazu Yamamoto; bpo-5913.)
The mimetypes module will now read the MIME database from
the Windows registry when initializing.
(Patch by Gabriel Genellina; bpo-4969.)
The path /Library/Python/2.7/site-packages is now appended to
sys.path, in order to share added packages between the system
installation and a user-installed copy of the same version.
(Changed by Ronald Oussoren; bpo-4865.)
在 2.7.13 版本发生变更: As of 2.7.13, this change was removed.
/Library/Python/2.7/site-packages, the site-packages directory
used by the Apple-supplied system Python 2.7 is no longer appended to
sys.path for user-installed Pythons such as from the python.org
installers. As of macOS 10.12, Apple changed how the system
site-packages directory is configured, which could cause installation
of pip components, like setuptools, to fail. Packages installed for
the system Python will no longer be shared with user-installed
Pythons. (bpo-28440)
FreeBSD 7.1's SO_SETFIB constant, used with the socket() methods
getsockopt()/setsockopt() to select an
alternate routing table, is now available in the socket
module. (Added by Kyle VanderBeek; bpo-8235.)
Two benchmark scripts, iobench and ccbench, were
added to the Tools directory. iobench measures the
speed of the built-in file I/O objects returned by open()
while performing various operations, and ccbench is a
concurrency benchmark that tries to measure computing throughput,
thread switching latency, and IO processing bandwidth when
performing several tasks using a varying number of threads.
The Tools/i18n/msgfmt.py script now understands plural
forms in .po files. (Fixed by Martin von Löwis;
bpo-5464.)
When importing a module from a .pyc or .pyo file
with an existing .py counterpart, the co_filename
attributes of the resulting code objects are overwritten when the
original filename is obsolete. This can happen if the file has been
renamed, moved, or is accessed through different paths. (Patch by
Ziga Seilnacht and Jean-Paul Calderone; bpo-1180193.)
The regrtest.py script now takes a --randseed=
switch that takes an integer that will be used as the random seed
for the -r option that executes tests in random order.
The -r option also reports the seed that was used
(Added by Collin Winter.)
Another regrtest.py switch is -j, which
takes an integer specifying how many tests run in parallel. This
allows reducing the total runtime on multi-core machines.
This option is compatible with several other options, including the
-R switch which is known to produce long runtimes.
(Added by Antoine Pitrou, bpo-6152.) This can also be used
with a new -F switch that runs selected tests in a loop
until they fail. (Added by Antoine Pitrou; bpo-7312.)
When executed as a script, the py_compile.py module now
accepts '-' as an argument, which will read standard input for
the list of filenames to be compiled. (Contributed by Piotr
Ożarowski; bpo-8233.)
本节列出了先前描述的改变以及可能需要修改你的代码的其他问题修正:
The range() function processes its arguments more
consistently; it will now call __int__() on non-float,
non-integer arguments that are supplied to it. (Fixed by Alexander
Belopolsky; bpo-1533.)
The string format() method changed the default precision used
for floating-point and complex numbers from 6 decimal
places to 12, which matches the precision used by str().
(Changed by Eric Smith; bpo-5920.)
Because of an optimization for the with statement, the special
methods __enter__() and __exit__() must belong to the object's
type, and cannot be directly attached to the object's instance. This
affects new-style classes (derived from object) and C extension
types. (bpo-6101.)
Due to a bug in Python 2.6, the exc_value parameter to
__exit__() methods was often the string representation of the
exception, not an instance. This was fixed in 2.7, so exc_value
will be an instance as expected. (Fixed by Florent Xicluna;
bpo-7853.)
When a restricted set of attributes were set using __slots__,
deleting an unset attribute would not raise AttributeError
as you would expect. Fixed by Benjamin Peterson; bpo-7604.)
在标准库中:
Operations with datetime instances that resulted in a year
falling outside the supported range didn't always raise
OverflowError. Such errors are now checked more carefully
and will now raise the exception. (Reported by Mark Leander, patch
by Anand B. Pillai and Alexander Belopolsky; bpo-7150.)
When using Decimal instances with a string's
format() method, the default alignment was previously
left-alignment. This has been changed to right-alignment, which might
change the output of your programs.
(Changed by Mark Dickinson; bpo-6857.)
Comparisons involving a signaling NaN value (or sNAN) now signal
InvalidOperation instead of silently returning a true or
false value depending on the comparison operator. Quiet NaN values
(or NaN) are now hashable. (Fixed by Mark Dickinson;
bpo-7279.)
The xml.etree.ElementTree library no longer escapes
ampersands and angle brackets when outputting an XML processing
instruction (which looks like <?xml-stylesheet href="#style1"?>)
or comment (which looks like <!-- comment -->).
(Patch by Neil Muller; bpo-2746.)
The readline() method of StringIO objects now does
nothing when a negative length is requested, as other file-like
objects do. (bpo-7348).
The syslog module will now use the value of sys.argv[0] as the
identifier instead of the previous default value of 'python'.
(Changed by Sean Reifschneider; bpo-8451.)
The tarfile module's default error handling has changed, to
no longer suppress fatal errors. The default error level was previously 0,
which meant that errors would only result in a message being written to the
debug log, but because the debug log is not activated by default,
these errors go unnoticed. The default error level is now 1,
which raises an exception if there's an error.
(Changed by Lars Gustäbel; bpo-7357.)
The urlparse module's urlsplit() now handles
unknown URL schemes in a fashion compliant with RFC 3986: if the
URL is of the form "<something>://...", the text before the
:// is treated as the scheme, even if it's a made-up scheme that
the module doesn't know about. This change may break code that
worked around the old behaviour. For example, Python 2.6.4 or 2.5
will return the following:
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', '', '//host/filename?query', '', '')
Python 2.7 (and Python 2.6.5) will return:
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', 'host', '/filename?query', '', '')
(Python 2.7 actually produces slightly different output, since it returns a named tuple instead of a standard tuple.)
对于C 扩展模块：
C extensions that use integer format codes with the PyArg_Parse*
family of functions will now raise a TypeError exception
instead of triggering a DeprecationWarning (bpo-5080).
Use the new PyOS_string_to_double() function instead of the old
PyOS_ascii_strtod() and PyOS_ascii_atof() functions,
which are now deprecated.
对于嵌入Python的应用程序：
The PySys_SetArgvEx() function was added, letting
applications close a security hole when the existing
PySys_SetArgv() function was used. Check whether you're
calling PySys_SetArgv() and carefully consider whether the
application should be using PySys_SetArgvEx() with
updatepath set to false.
New features may be added to Python 2.7 maintenance releases when the situation genuinely calls for it. Any such additions must go through the Python Enhancement Proposal process, and make a compelling case for why they can't be adequately addressed by either adding the new feature solely to Python 3, or else by publishing it on the Python Package Index.
In addition to the specific proposals listed below, there is a general
exemption allowing new -3 warnings to be added in any Python 2.7
maintenance release.
In debug mode, the [xxx refs] statistic is not written by default, the
PYTHONSHOWREFCOUNT environment variable now must also be set.
(Contributed by Victor Stinner; bpo-31733.)
When Python is compiled with COUNT_ALLOC defined, allocation counts are no
longer dumped by default anymore: the PYTHONSHOWALLOCCOUNT environment
variable must now also be set. Moreover, allocation counts are now dumped into
stderr, rather than stdout. (Contributed by Victor Stinner; bpo-31692.)
Added in version 2.7.15.
PEP 434 describes a general exemption for changes made to the IDLE development environment shipped along with Python. This exemption makes it possible for the IDLE developers to provide a more consistent user experience across all supported versions of Python 2 and 3.
For details of any IDLE changes, refer to the NEWS file for the specific release.
PEP 466 describes a number of network security enhancement proposals that have been approved for inclusion in Python 2.7 maintenance releases, with the first of those changes appearing in the Python 2.7.7 release.
PEP 466 Python 2.7.7 中添加的相关功能：
hmac.compare_digest() was backported from Python 3 to make a timing
attack resistant comparison operation available to Python 2 applications.
(Contributed by Alex Gaynor; bpo-21306.)
OpenSSL 1.0.1g was upgraded in the official Windows installers published on python.org. (Contributed by Zachary Ware; bpo-21462.)
PEP 466 Python 2.7.8 中添加的相关功能：
hashlib.pbkdf2_hmac() was backported from Python 3 to make a hashing
algorithm suitable for secure password storage broadly available to Python
2 applications. (Contributed by Alex Gaynor; bpo-21304.)
OpenSSL 1.0.1h was upgraded for the official Windows installers published on python.org. (Contributed by Zachary Ware in bpo-21671 for CVE 2014-0224.)
PEP 466 Python 2.7.9 中添加的相关功能：
Most of Python 3.4's ssl module was backported. This means ssl
now supports Server Name Indication, TLS1.x settings, access to the platform
certificate store, the SSLContext class, and other
features. (Contributed by Alex Gaynor and David Reid; bpo-21308.)
Refer to the "Version added: 2.7.9" notes in the module documentation for specific details.
os.urandom() was changed to cache a file descriptor to /dev/urandom
instead of reopening /dev/urandom on every call. (Contributed by Alex
Gaynor; bpo-21305.)
hashlib.algorithms_guaranteed and
hashlib.algorithms_available were backported from Python 3 to make
it easier for Python 2 applications to select the strongest available hash
algorithm. (Contributed by Alex Gaynor in bpo-21307)
PEP 477 approves the inclusion of the PEP 453 ensurepip module and the improved documentation that was enabled by it in the Python 2.7 maintenance releases, appearing first in the Python 2.7.9 release.
The new ensurepip module (defined in PEP 453) provides a standard
cross-platform mechanism to bootstrap the pip installer into Python
installations. The version of pip included with Python 2.7.9 is pip
1.5.6, and future 2.7.x maintenance releases will update the bundled version to
the latest version of pip that is available at the time of creating the
release candidate.
By default, the commands pip, pipX and pipX.Y will be installed on
all platforms (where X.Y stands for the version of the Python installation),
along with the pip Python package and its dependencies.
For CPython source builds on POSIX systems,
the make install and make altinstall commands do not bootstrap pip
by default. This behaviour can be controlled through configure options, and
overridden through Makefile options.
在 Windows 和 Mac OS X 上，现在 CPython 安装程序默认会将 pip 与 CPython 本身一同安装（用户可以在安装过程中选择不安装它）。 Window 用户需要选择执行 PATH 修改以使 pip 在命令行中默认可用，在其他情况下它仍然可以通过 Windows 版 Python 启动器以 py -m pip 的方式使用。
As discussed in the PEP, platform packagers may choose not to install these commands by default, as long as, when invoked, they provide clear and simple directions on how to install them on that platform (usually using the system package manager).
作为此项更改的一部分，文档的 安装 Python 模块 和 分发 Python 模块 章节已经完全重新设计，快速入门和 FAQ 文档也是如此。 大部分打包指南文档现在都已被移至由 Python Packaging Authority 维护的 Python Packaging User Guide 以及相应的独立项目文档。
不过，由于目前迁移过程尚未完成，这些指南的旧版本仍然可通过 使用 setuptools 构建 C 和 C++ 扩展 和 使用 setuptools 构建 C 和 C++ 扩展 来访问。
参见
PEP 476 updated httplib and modules which use it, such as
urllib2 and xmlrpclib, to now
verify that the server
presents a certificate which is signed by a Certificate Authority in the
platform trust store and whose hostname matches the hostname being requested
by default, significantly improving security for many applications. This
change was made in the Python 2.7.9 release.
对于需要之前版本的旧有行为的应用程序，可以传入一个替代的上下文:
import urllib2
import ssl
# This disables all verification
context = ssl._create_unverified_context()
# This allows using a specific certificate for the host, which doesn't need
# to be in the trust store
context = ssl.create_default_context(cafile="/path/to/file.crt")
urllib2.urlopen("https://invalid-cert", context=context)
PEP 493 provides additional migration tools to support a more incremental infrastructure upgrade process for environments containing applications and services relying on the historically permissive processing of server certificates when establishing client HTTPS connections. These additions were made in the Python 2.7.12 release.
These tools are intended for use in cases where affected applications and services can't be modified to explicitly pass a more permissive SSL context when establishing the connection.
For applications and services which can't be modified at all, the new
PYTHONHTTPSVERIFY environment variable may be set to 0 to revert an
entire Python process back to the default permissive behaviour of Python 2.7.8
and earlier.
For cases where the connection establishment code can't be modified, but the
overall application can be, the new ssl._https_verify_certificates()
function can be used to adjust the default behaviour at runtime.
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。）
Added in version 2.7.14.
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 2.7.14 版本发生变更.
作者要感谢以下人员为本文的各种草案提供建议，更正和帮助： Nick Coghlan, Philip Jenvey, Ryan Lovett, R. David Murray, Hugh Secker-Walker.