Python 3.3.2官方文档：关键更新与特性概览

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本资源是Python v3.3.2官方文档，提供了该版本的主要更新内容和改进。以下是一些关键知识点： 1. **概览与亮点** - 该版本的文档总结了Python 3.3.2的主要新功能和改进，包括对开发环境的支持（PEP 405: Virtual Environments），更好地管理命名空间（PEP 420: Implicit Namespace Packages），以及内存视图的增强实现（PEP 3118）。 2. **PEP 405: Virtual Environments** - 这个提议引入了虚拟环境的概念，允许开发者在不干扰全局环境的前提下创建隔离的工作环境，有助于管理和避免库之间的依赖冲突。 3. **PEP 420: Implicit Namespace Packages** - 提供了一种更自然的方式来组织模块，使得包内的子包无需显式声明即可被其他包自动识别。 4. **内存视图和缓冲协议** - 新的内存视图API（PEP 3118）提高了数据处理的灵活性和效率，同时也更新了缓冲协议的文档，以便更好地理解和使用。 5. **PEP 393: Flexible String Representation** - 改进了字符串对象的表示方式，提供更灵活的功能和性能优化。 6. **PEP 397: Python Launcher for Windows** - 针对Windows用户，提供了更便捷的Python启动器，简化了安装和配置过程。 7. **PEP 3151: Reworking the OS and IO Exception Hierarchy** - 对异常分类进行了重新设计，有助于提高代码的可读性和错误处理的统一性。 8. **PEP 380: Syntax for Delegating to a Subgenerator** - 引入新的语法，使开发者能更方便地处理生成器的嵌套调用和委派。 9. **异常上下文抑制（PEP 409）** - 提供了一种机制来控制异常上下文的传播，有助于更精细的错误处理。 10. **明确的Unicode字面量（PEP 414）** - 强制使用明确的`u`前缀表示Unicode字符串，提高了代码的可读性和一致性。 11. **类和函数的限定名称（PEP 3155）** - 改进类和函数的命名规则，提供更强的标识和区分度。 12. **键共享字典（PEP 412）** - 一种新的数据结构，支持高效地共享字典中的键。 13. **函数签名对象（PEP 362）** - 提供了更易操作的函数签名表示，便于理解和重构。 14. **sys.implementation模块的添加（PEP 421）** - 为系统实现提供了更统一的访问接口，包括`SimpleNamespace`用于创建简单的命名空间对象。 15. **importlib作为导入实现的替代（PEP 412）** - 介绍新的API，提升了导入模块的性能和管理方式，同时带来了可见性变化。 16. **其他语言变更** - 除了上述重点，还有其他语法、库或特性方面的调整，可能包括性能提升、错误处理改进等。 17. **更细粒度的导入锁（PEP 421）** - 为了提高多线程环境下代码的并发性，引入了更加细致的导入锁策略。 18. **内置函数改进** - 文档还可能包含了对标准库内置函数的优化和更新说明。通过阅读这份文档，开发者可以了解到Python 3.3.2版本的具体改进，帮助他们在编程实践中更好地利用这些新功能，提升代码质量与性能。

19.2 ipaddress

The new ipaddress module provides tools for creating and manipulating objects representing IPv4 and IPv6

addresses, networks and interfaces (i.e. an IP address associated with a speciﬁc IP subnet).

(Contributed by Google and Peter Moody in PEP 3144)

19.3 lzma

The newly-added lzma module provides data compression and decompression using the LZMA algorithm, in-

cluding support for the .xz and .lzma ﬁle formats.

(Contributed by Nadeem Vawda and Per Øyvind Karlsen in issue 6715)

20 Improved Modules

20.1 abc

Improved support for abstract base classes containing descriptors composed with abstract methods. The recom-

mended approach to declaring abstract descriptors is now to provide __isabstractmethod__ as a dynami-

cally updated property. The built-in descriptors have been updated accordingly.

• abc.abstractproperty has been deprecated, use property with abc.abstractmethod() in-

stead.

• abc.abstractclassmethod has been deprecated, use classmethod with

abc.abstractmethod() instead.

• abc.abstractstaticmethod has been deprecated, use staticmethod with

abc.abstractmethod() instead.

(Contributed by Darren Dale in issue 11610)

abc.ABCMeta.register() now returns the registered subclass, which means it can now be used as a class

decorator (issue 10868).

20.2 array

The array module supports the long long type using q and Q type codes.

(Contributed by Oren Tirosh and Hirokazu Yamamoto in issue 1172711)

20.3 base64

ASCII-only Unicode strings are now accepted by the decoding functions of the base64 modern interface. For

example, base64.b64decode(’YWJj’) returns b’abc’. (Contributed by Catalin Iacob in issue 13641.)

20.4 binascii

In addition to the binary objects they normally accept, the a2b_ functions now all also accept ASCII-only strings

as input. (Contributed by Antoine Pitrou in issue 13637.)

20.5 bz2

The bz2 module has been rewritten from scratch. In the process, several new features have been added:

• New bz2.open() function: open a bzip2-compressed ﬁle in binary or text mode.

• bz2.BZ2File can now read from and write to arbitrary ﬁle-like objects, by means of its constructor’s

ﬁleobj argument.

(Contributed by Nadeem Vawda in issue 5863)

• bz2.BZ2File and bz2.decompress() can now decompress multi-stream inputs (such as those pro-

duced by the pbzip2 tool). bz2.BZ2File can now also be used to create this type of ﬁle, using the ’a’

(append) mode.

(Contributed by Nir Aides in issue 1625)

• bz2.BZ2File now implements all of the io.BufferedIOBase API, except for the detach() and

truncate() methods.

20.6 codecs

The mbcs codec has been rewritten to handle correctly replace and ignore error handlers on all Windows

versions. The mbcs codec now supports all error handlers, instead of only replace to encode and ignore to

decode.

A new Windows-only codec has been added: cp65001 (issue 13216). It is the Windows code page 65001

(Windows UTF-8, CP_UTF8). For example, it is used by sys.stdout if the console output code page is set to

cp65001 (e.g., using chcp 65001 command).

Multibyte CJK decoders now resynchronize faster. They only ignore the ﬁrst byte of an invalid byte sequence. For

example, b’\xff\n’.decode(’gb2312’, ’replace’) now returns a \n after the replacement charac-

ter.

(issue 12016)

Incremental CJK codec encoders are no longer reset at each call to their encode() methods. For example:

$ ./python -q

>>> import codecs

>>> encoder = codecs.getincrementalencoder(’hz’)(’strict’)

>>> b’’.join(encoder.encode(x) for x in ’\u52ff\u65bd\u65bc\u4eba\u3002 Bye.’)

b’~{NpJ)l6HK!#~} Bye.’

This example gives b’~{Np~}~{J)~}~{l6~}~{HK~}~{!#~} Bye.’ with older Python versions.

(issue 12100)

The unicode_internal codec has been deprecated.

20.7 collections

Addition of a new ChainMap class to allow treating a number of mappings as a single unit. (Written by Raymond

Hettinger for issue 11089, made public in issue 11297)

The abstract base classes have been moved in a new collections.abc module, to better differentiate between

the abstract and the concrete collections classes. Aliases for ABCs are still present in the collections module

to preserve existing imports. (issue 11085)

The Counter class now supports the unary + and - operators, as well as the in-place operators +=, -=, |=, and

&=. (Contributed by Raymond Hettinger in issue 13121.)

20.8 contextlib

ExitStack now provides a solid foundation for programmatic manipulation of context managers and similar

cleanup functionality. Unlike the previous contextlib.nested API (which was deprecated and removed),

the new API is designed to work correctly regardless of whether context managers acquire their resources in their

__init__ method (for example, ﬁle objects) or in their __enter__ method (for example, synchronisation

objects from the threading module).

(issue 13585)

20.9 crypt

Addition of salt and modular crypt format (hashing method) and the mksalt() function to the crypt module.

(issue 10924)

20.10 curses

• If the curses module is linked to the ncursesw library, use Unicode functions when Unicode strings or

characters are passed (e.g. waddwstr()), and bytes functions otherwise (e.g. waddstr()).

• Use the locale encoding instead of utf-8 to encode Unicode strings.

• curses.window has a new curses.window.encoding attribute.

• The curses.window class has a new get_wch() method to get a wide character

• The curses module has a new unget_wch() function to push a wide character so the next get_wch()

will return it

(Contributed by Iñigo Serna in issue 6755)

20.11 datetime

• Equality comparisons between naive and aware datetime instances now return False instead of raising

TypeError (issue 15006).

• New datetime.datetime.timestamp() method: Return POSIX timestamp corresponding to the

datetime instance.

• The datetime.datetime.strftime() method supports formatting years older than 1000.

• The datetime.datetime.astimezone() method can now be called without arguments to convert

datetime instance to the system timezone.

20.12 decimal

issue 7652 - integrate fast native decimal arithmetic. C-module and libmpdec written by Stefan Krah.

The new C version of the decimal module integrates the high speed libmpdec library for arbitrary precision

correctly-rounded decimal ﬂoating point arithmetic. libmpdec conforms to IBM’s General Decimal Arithmetic

Speciﬁcation.

Performance gains range from 10x for database applications to 100x for numerically intensive applications. These

numbers are expected gains for standard precisions used in decimal ﬂoating point arithmetic. Since the precision

is user conﬁgurable, the exact ﬁgures may vary. For example, in integer bignum arithmetic the differences can be

signiﬁcantly higher.

The following table is meant as an illustration. Benchmarks are available at

http://www.bytereef.org/mpdecimal/quickstart.html.

decimal.py _decimal speedup

pi 42.02s 0.345s 120x

telco 172.19s 5.68s 30x

psycopg 3.57s 0.29s 12x

Features

• The FloatOperation signal optionally enables stricter semantics for mixing ﬂoats and Decimals.

• If Python is compiled without threads, the C version automatically disables the expensive thread local

context machinery. In this case, the variable HAVE_THREADS is set to False.

API changes

• The C module has the following context limits, depending on the machine architecture:

32-bit 64-bit

MAX_PREC 425000000 999999999999999999

MAX_EMAX 425000000 999999999999999999

MIN_EMIN -425000000 -999999999999999999

• In the context templates (DefaultContext, BasicContext and ExtendedContext) the magni-

tude of Emax and Emin has changed to 999999.

• The Decimal constructor in decimal.py does not observe the context limits and converts values with arbi-

trary exponents or precision exactly. Since the C version has internal limits, the following scheme is used:

If possible, values are converted exactly, otherwise InvalidOperation is raised and the result is NaN.

In the latter case it is always possible to use create_decimal() in order to obtain a rounded or inexact

value.

• The power function in decimal.py is always correctly-rounded. In the C version, it is deﬁned in terms of

the correctly-rounded exp() and ln() functions, but the ﬁnal result is only “almost always correctly

rounded”.

• In the C version, the context dictionary containing the signals is a MutableMapping. For speed reasons,

flags and traps always refer to the same MutableMapping that the context was initialized with. If

a new signal dictionary is assigned, flags and traps are updated with the new values, but they do not

reference the RHS dictionary.

• Pickling a Context produces a different output in order to have a common interchange format for the

Python and C versions.

• The order of arguments in the Context constructor has been changed to match the order displayed by

repr().

• The watchexp parameter in the quantize() method is deprecated.

20.13 email

Policy Framework

The email package now has a policy framework. A Policy is an object with several methods and properties

that control how the email package behaves. The primary policy for Python 3.3 is the Compat32 policy, which

provides backward compatibility with the email package in Python 3.2. A policy can be speciﬁed when an

email message is parsed by a parser, or when a Message object is created, or when an email is serialized

using a generator. Unless overridden, a policy passed to a parser is inherited by all the Message object

and sub-objects created by the parser. By default a generator will use the policy of the Message object it

is serializing. The default policy is compat32.

The minimum set of controls implemented by all policy objects are:

max_line_length The maximum length, excluding the linesep character(s), individual lines

may have when a Message is serialized. Defaults to 78.

linesep The character used to separate individual lines when a Message is

serialized. Defaults to \n.

cte_type 7bit or 8bit. 8bit applies only to a Bytes generator, and means

that non-ASCII may be used where allowed by the protocol (or where it

exists in the original input).

raise_on_defect Causes a parser to raise error when defects are encountered instead of

adding them to the Message object’s defects list.

A new policy instance, with new settings, is created using the clone() method of policy objects. clone takes

any of the above controls as keyword arguments. Any control not speciﬁed in the call retains its default value.

Thus you can create a policy that uses \r\n linesep characters like this:

mypolicy = compat32.clone(linesep=’\r\n’)

Policies can be used to make the generation of messages in the format needed by your application simpler. Instead

of having to remember to specify linesep=’\r\n’ in all the places you call a generator, you can specify

it once, when you set the policy used by the parser or the Message, whichever your program uses to create

Message objects. On the other hand, if you need to generate messages in multiple forms, you can still specify

the parameters in the appropriate generator call. Or you can have custom policy instances for your different

cases, and pass those in when you create the generator.

Provisional Policy with New Header API

While the policy framework is worthwhile all by itself, the main motivation for introducing it is to allow the

creation of new policies that implement new features for the email package in a way that maintains backward

compatibility for those who do not use the new policies. Because the new policies introduce a new API, we

are releasing them in Python 3.3 as a provisional policy. Backwards incompatible changes (up to and including

removal of the code) may occur if deemed necessary by the core developers.

The new policies are instances of EmailPolicy, and add the following additional controls:

refold_source Controls whether or not headers parsed by a parser are refolded by the

generator. It can be none, long, or all. The default is long, which

means that source headers with a line longer than max_line_length get

refolded. none means no line get refolded, and all means that all lines get

refolded.

header_factory A callable that take a name and value and produces a custom header object.

The header_factory is the key to the new features provided by the new policies. When one of the new policies

is used, any header retrieved from a Message object is an object produced by the header_factory, and any

time you set a header on a Message it becomes an object produced by header_factory. All such header

objects have a name attribute equal to the header name. Address and Date headers have additional attributes that

give you access to the parsed data of the header. This means you can now do things like this:

>>> m = Message(policy=SMTP)

>>> m[’To’] = ’Éric <foo@example.com>’

>>> m[’to’]

’Éric <foo@example.com>’

>>> m[’to’].addresses

(Address(display_name=’Éric’, username=’foo’, domain=’example.com’),)

>>> m[’to’].addresses[0].username

’foo’

>>> m[’to’].addresses[0].display_name

’Éric’

>>> m[’Date’] = email.utils.localtime()

>>> m[’Date’].datetime

datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), ’EDT’))

>>> m[’Date’]

’Fri, 25 May 2012 21:44:27 -0400’

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