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diff --git a/Doc/whatsnew/3.2.rst b/Doc/whatsnew/3.2.rst new file mode 100644 index 0000000..d411d85 --- /dev/null +++ b/Doc/whatsnew/3.2.rst @@ -0,0 +1,2704 @@ +**************************** + What's New In Python 3.2 +**************************** + +:Author: Raymond Hettinger +:Release: |release| +:Date: |today| + +.. $Id$ + Rules for maintenance: + + * Anyone can add text to this document. Do not spend very much time + on the wording of your changes, because your text will probably + get rewritten. (Note, during release candidate phase or just before + a beta release, please use the tracker instead -- this helps avoid + merge conflicts. If you must add a suggested entry directly, + please put it in an XXX comment and the maintainer will take notice). + + * The maintainer will go through Misc/NEWS periodically and add + changes; it's therefore more important to add your changes to + Misc/NEWS than to this file. + + * This is not a complete list of every single change; completeness + is the purpose of Misc/NEWS. Some changes I consider too small + or esoteric to include. If such a change is added to the text, + I'll just remove it. (This is another reason you shouldn't spend + too much time on writing your addition.) + + * If you want to draw your new text to the attention of the + maintainer, add 'XXX' to the beginning of the paragraph or + section. + + * It's OK to just add a fragmentary note about a change. For + example: "XXX Describe the transmogrify() function added to the + socket module." The maintainer will research the change and + write the necessary text. + + * You can comment out your additions if you like, but it's not + necessary (especially when a final release is some months away). + + * Credit the author of a patch or bugfix. Just the name is + sufficient; the e-mail address isn't necessary. It's helpful to + add the issue number: + + XXX Describe the transmogrify() function added to the socket + module. + + (Contributed by P.Y. Developer; :issue:`12345`.) + + This saves the maintainer the effort of going through the SVN log + when researching a change. + +This article explains the new features in Python 3.2 as compared to 3.1. It +focuses on a few highlights and gives a few examples. For full details, see the +:source:`Misc/NEWS <Misc/NEWS>` file. + +.. seealso:: + + :pep:`392` - Python 3.2 Release Schedule + + +PEP 384: Defining a Stable ABI +============================== + +In the past, extension modules built for one Python version were often +not usable with other Python versions. Particularly on Windows, every +feature release of Python required rebuilding all extension modules that +one wanted to use. This requirement was the result of the free access to +Python interpreter internals that extension modules could use. + +With Python 3.2, an alternative approach becomes available: extension +modules which restrict themselves to a limited API (by defining +Py_LIMITED_API) cannot use many of the internals, but are constrained +to a set of API functions that are promised to be stable for several +releases. As a consequence, extension modules built for 3.2 in that +mode will also work with 3.3, 3.4, and so on. Extension modules that +make use of details of memory structures can still be built, but will +need to be recompiled for every feature release. + +.. seealso:: + + :pep:`384` - Defining a Stable ABI + PEP written by Martin von Löwis. + + +PEP 389: Argparse Command Line Parsing Module +============================================= + +A new module for command line parsing, :mod:`argparse`, was introduced to +overcome the limitations of :mod:`optparse` which did not provide support for +positional arguments (not just options), subcommands, required options and other +common patterns of specifying and validating options. + +This module has already had widespread success in the community as a +third-party module. Being more fully featured than its predecessor, the +:mod:`argparse` module is now the preferred module for command-line processing. +The older module is still being kept available because of the substantial amount +of legacy code that depends on it. + +Here's an annotated example parser showing features like limiting results to a +set of choices, specifying a *metavar* in the help screen, validating that one +or more positional arguments is present, and making a required option:: + + import argparse + parser = argparse.ArgumentParser( + description = 'Manage servers', # main description for help + epilog = 'Tested on Solaris and Linux') # displayed after help + parser.add_argument('action', # argument name + choices = ['deploy', 'start', 'stop'], # three allowed values + help = 'action on each target') # help msg + parser.add_argument('targets', + metavar = 'HOSTNAME', # var name used in help msg + nargs = '+', # require one or more targets + help = 'url for target machines') # help msg explanation + parser.add_argument('-u', '--user', # -u or --user option + required = True, # make it a required argument + help = 'login as user') + +Example of calling the parser on a command string:: + + >>> cmd = 'deploy sneezy.example.com sleepy.example.com -u skycaptain' + >>> result = parser.parse_args(cmd.split()) + >>> result.action + 'deploy' + >>> result.targets + ['sneezy.example.com', 'sleepy.example.com'] + >>> result.user + 'skycaptain' + +Example of the parser's automatically generated help:: + + >>> parser.parse_args('-h'.split()) + + usage: manage_cloud.py [-h] -u USER + {deploy,start,stop} HOSTNAME [HOSTNAME ...] + + Manage servers + + positional arguments: + {deploy,start,stop} action on each target + HOSTNAME url for target machines + + optional arguments: + -h, --help show this help message and exit + -u USER, --user USER login as user + + Tested on Solaris and Linux + +An especially nice :mod:`argparse` feature is the ability to define subparsers, +each with their own argument patterns and help displays:: + + import argparse + parser = argparse.ArgumentParser(prog='HELM') + subparsers = parser.add_subparsers() + + parser_l = subparsers.add_parser('launch', help='Launch Control') # first subgroup + parser_l.add_argument('-m', '--missiles', action='store_true') + parser_l.add_argument('-t', '--torpedos', action='store_true') + + parser_m = subparsers.add_parser('move', help='Move Vessel', # second subgroup + aliases=('steer', 'turn')) # equivalent names + parser_m.add_argument('-c', '--course', type=int, required=True) + parser_m.add_argument('-s', '--speed', type=int, default=0) + + $ ./helm.py --help # top level help (launch and move) + $ ./helm.py launch --help # help for launch options + $ ./helm.py launch --missiles # set missiles=True and torpedos=False + $ ./helm.py steer --course 180 --speed 5 # set movement parameters + +.. seealso:: + + :pep:`389` - New Command Line Parsing Module + PEP written by Steven Bethard. + + :ref:`upgrading-optparse-code` for details on the differences from :mod:`optparse`. + + +PEP 391: Dictionary Based Configuration for Logging +==================================================== + +The :mod:`logging` module provided two kinds of configuration, one style with +function calls for each option or another style driven by an external file saved +in a :mod:`ConfigParser` format. Those options did not provide the flexibility +to create configurations from JSON or YAML files, nor did they support +incremental configuration, which is needed for specifying logger options from a +command line. + +To support a more flexible style, the module now offers +:func:`logging.config.dictConfig` for specifying logging configuration with +plain Python dictionaries. The configuration options include formatters, +handlers, filters, and loggers. Here's a working example of a configuration +dictionary:: + + {"version": 1, + "formatters": {"brief": {"format": "%(levelname)-8s: %(name)-15s: %(message)s"}, + "full": {"format": "%(asctime)s %(name)-15s %(levelname)-8s %(message)s"} + }, + "handlers": {"console": { + "class": "logging.StreamHandler", + "formatter": "brief", + "level": "INFO", + "stream": "ext://sys.stdout"}, + "console_priority": { + "class": "logging.StreamHandler", + "formatter": "full", + "level": "ERROR", + "stream": "ext://sys.stderr"} + }, + "root": {"level": "DEBUG", "handlers": ["console", "console_priority"]}} + + +If that dictionary is stored in a file called :file:`conf.json`, it can be +loaded and called with code like this:: + + >>> import json, logging.config + >>> with open('conf.json') as f: + conf = json.load(f) + >>> logging.config.dictConfig(conf) + >>> logging.info("Transaction completed normally") + INFO : root : Transaction completed normally + >>> logging.critical("Abnormal termination") + 2011-02-17 11:14:36,694 root CRITICAL Abnormal termination + +.. seealso:: + + :pep:`391` - Dictionary Based Configuration for Logging + PEP written by Vinay Sajip. + + +PEP 3148: The ``concurrent.futures`` module +============================================ + +Code for creating and managing concurrency is being collected in a new top-level +namespace, *concurrent*. Its first member is a *futures* package which provides +a uniform high-level interface for managing threads and processes. + +The design for :mod:`concurrent.futures` was inspired by +*java.util.concurrent.package*. In that model, a running call and its result +are represented by a :class:`~concurrent.futures.Future` object that abstracts +features common to threads, processes, and remote procedure calls. That object +supports status checks (running or done), timeouts, cancellations, adding +callbacks, and access to results or exceptions. + +The primary offering of the new module is a pair of executor classes for +launching and managing calls. The goal of the executors is to make it easier to +use existing tools for making parallel calls. They save the effort needed to +setup a pool of resources, launch the calls, create a results queue, add +time-out handling, and limit the total number of threads, processes, or remote +procedure calls. + +Ideally, each application should share a single executor across multiple +components so that process and thread limits can be centrally managed. This +solves the design challenge that arises when each component has its own +competing strategy for resource management. + +Both classes share a common interface with three methods: +:meth:`~concurrent.futures.Executor.submit` for scheduling a callable and +returning a :class:`~concurrent.futures.Future` object; +:meth:`~concurrent.futures.Executor.map` for scheduling many asynchronous calls +at a time, and :meth:`~concurrent.futures.Executor.shutdown` for freeing +resources. The class is a :term:`context manager` and can be used in a +:keyword:`with` statement to assure that resources are automatically released +when currently pending futures are done executing. + +A simple of example of :class:`~concurrent.futures.ThreadPoolExecutor` is a +launch of four parallel threads for copying files:: + + import concurrent.futures, shutil + with concurrent.futures.ThreadPoolExecutor(max_workers=4) as e: + e.submit(shutil.copy, 'src1.txt', 'dest1.txt') + e.submit(shutil.copy, 'src2.txt', 'dest2.txt') + e.submit(shutil.copy, 'src3.txt', 'dest3.txt') + e.submit(shutil.copy, 'src4.txt', 'dest4.txt') + +.. seealso:: + + :pep:`3148` - Futures -- Execute Computations Asynchronously + PEP written by Brian Quinlan. + + :ref:`Code for Threaded Parallel URL reads<threadpoolexecutor-example>`, an + example using threads to fetch multiple web pages in parallel. + + :ref:`Code for computing prime numbers in + parallel<processpoolexecutor-example>`, an example demonstrating + :class:`~concurrent.futures.ProcessPoolExecutor`. + + +PEP 3147: PYC Repository Directories +===================================== + +Python's scheme for caching bytecode in *.pyc* files did not work well in +environments with multiple Python interpreters. If one interpreter encountered +a cached file created by another interpreter, it would recompile the source and +overwrite the cached file, thus losing the benefits of caching. + +The issue of "pyc fights" has become more pronounced as it has become +commonplace for Linux distributions to ship with multiple versions of Python. +These conflicts also arise with CPython alternatives such as Unladen Swallow. + +To solve this problem, Python's import machinery has been extended to use +distinct filenames for each interpreter. Instead of Python 3.2 and Python 3.3 and +Unladen Swallow each competing for a file called "mymodule.pyc", they will now +look for "mymodule.cpython-32.pyc", "mymodule.cpython-33.pyc", and +"mymodule.unladen10.pyc". And to prevent all of these new files from +cluttering source directories, the *pyc* files are now collected in a +"__pycache__" directory stored under the package directory. + +Aside from the filenames and target directories, the new scheme has a few +aspects that are visible to the programmer: + +* Imported modules now have a :attr:`__cached__` attribute which stores the name + of the actual file that was imported: + + >>> import collections + >>> collections.__cached__ + 'c:/py32/lib/__pycache__/collections.cpython-32.pyc' + +* The tag that is unique to each interpreter is accessible from the :mod:`imp` + module: + + >>> import imp + >>> imp.get_tag() + 'cpython-32' + +* Scripts that try to deduce source filename from the imported file now need to + be smarter. It is no longer sufficient to simply strip the "c" from a ".pyc" + filename. Instead, use the new functions in the :mod:`imp` module: + + >>> imp.source_from_cache('c:/py32/lib/__pycache__/collections.cpython-32.pyc') + 'c:/py32/lib/collections.py' + >>> imp.cache_from_source('c:/py32/lib/collections.py') + 'c:/py32/lib/__pycache__/collections.cpython-32.pyc' + +* The :mod:`py_compile` and :mod:`compileall` modules have been updated to + reflect the new naming convention and target directory. The command-line + invocation of *compileall* has new options: ``-i`` for + specifying a list of files and directories to compile and ``-b`` which causes + bytecode files to be written to their legacy location rather than + *__pycache__*. + +* The :mod:`importlib.abc` module has been updated with new :term:`abstract base + classes <abstract base class>` for loading bytecode files. The obsolete + ABCs, :class:`~importlib.abc.PyLoader` and + :class:`~importlib.abc.PyPycLoader`, have been deprecated (instructions on how + to stay Python 3.1 compatible are included with the documentation). + +.. seealso:: + + :pep:`3147` - PYC Repository Directories + PEP written by Barry Warsaw. + + +PEP 3149: ABI Version Tagged .so Files +====================================== + +The PYC repository directory allows multiple bytecode cache files to be +co-located. This PEP implements a similar mechanism for shared object files by +giving them a common directory and distinct names for each version. + +The common directory is "pyshared" and the file names are made distinct by +identifying the Python implementation (such as CPython, PyPy, Jython, etc.), the +major and minor version numbers, and optional build flags (such as "d" for +debug, "m" for pymalloc, "u" for wide-unicode). For an arbitrary package "foo", +you may see these files when the distribution package is installed:: + + /usr/share/pyshared/foo.cpython-32m.so + /usr/share/pyshared/foo.cpython-33md.so + +In Python itself, the tags are accessible from functions in the :mod:`sysconfig` +module:: + + >>> import sysconfig + >>> sysconfig.get_config_var('SOABI') # find the version tag + 'cpython-32mu' + >>> sysconfig.get_config_var('SO') # find the full filename extension + '.cpython-32mu.so' + +.. seealso:: + + :pep:`3149` - ABI Version Tagged .so Files + PEP written by Barry Warsaw. + + +PEP 3333: Python Web Server Gateway Interface v1.0.1 +===================================================== + +This informational PEP clarifies how bytes/text issues are to be handled by the +WGSI protocol. The challenge is that string handling in Python 3 is most +conveniently handled with the :class:`str` type even though the HTTP protocol +is itself bytes oriented. + +The PEP differentiates so-called *native strings* that are used for +request/response headers and metadata versus *byte strings* which are used for +the bodies of requests and responses. + +The *native strings* are always of type :class:`str` but are restricted to code +points between *U+0000* through *U+00FF* which are translatable to bytes using +*Latin-1* encoding. These strings are used for the keys and values in the +environment dictionary and for response headers and statuses in the +:func:`start_response` function. They must follow :rfc:`2616` with respect to +encoding. That is, they must either be *ISO-8859-1* characters or use +:rfc:`2047` MIME encoding. + +For developers porting WSGI applications from Python 2, here are the salient +points: + +* If the app already used strings for headers in Python 2, no change is needed. + +* If instead, the app encoded output headers or decoded input headers, then the + headers will need to be re-encoded to Latin-1. For example, an output header + encoded in utf-8 was using ``h.encode('utf-8')`` now needs to convert from + bytes to native strings using ``h.encode('utf-8').decode('latin-1')``. + +* Values yielded by an application or sent using the :meth:`write` method + must be byte strings. The :func:`start_response` function and environ + must use native strings. The two cannot be mixed. + +For server implementers writing CGI-to-WSGI pathways or other CGI-style +protocols, the users must to be able access the environment using native strings +even though the underlying platform may have a different convention. To bridge +this gap, the :mod:`wsgiref` module has a new function, +:func:`wsgiref.handlers.read_environ` for transcoding CGI variables from +:attr:`os.environ` into native strings and returning a new dictionary. + +.. seealso:: + + :pep:`3333` - Python Web Server Gateway Interface v1.0.1 + PEP written by Phillip Eby. + + +Other Language Changes +====================== + +Some smaller changes made to the core Python language are: + +* String formatting for :func:`format` and :meth:`str.format` gained new + capabilities for the format character **#**. Previously, for integers in + binary, octal, or hexadecimal, it caused the output to be prefixed with '0b', + '0o', or '0x' respectively. Now it can also handle floats, complex, and + Decimal, causing the output to always have a decimal point even when no digits + follow it. + + >>> format(20, '#o') + '0o24' + >>> format(12.34, '#5.0f') + ' 12.' + + (Suggested by Mark Dickinson and implemented by Eric Smith in :issue:`7094`.) + +* There is also a new :meth:`str.format_map` method that extends the + capabilities of the existing :meth:`str.format` method by accepting arbitrary + :term:`mapping` objects. This new method makes it possible to use string + formatting with any of Python's many dictionary-like objects such as + :class:`~collections.defaultdict`, :class:`~shelve.Shelf`, + :class:`~configparser.ConfigParser`, or :mod:`dbm`. It is also useful with + custom :class:`dict` subclasses that normalize keys before look-up or that + supply a :meth:`__missing__` method for unknown keys:: + + >>> import shelve + >>> d = shelve.open('tmp.shl') + >>> 'The {project_name} status is {status} as of {date}'.format_map(d) + 'The testing project status is green as of February 15, 2011' + + >>> class LowerCasedDict(dict): + def __getitem__(self, key): + return dict.__getitem__(self, key.lower()) + >>> lcd = LowerCasedDict(part='widgets', quantity=10) + >>> 'There are {QUANTITY} {Part} in stock'.format_map(lcd) + 'There are 10 widgets in stock' + + >>> class PlaceholderDict(dict): + def __missing__(self, key): + return '<{}>'.format(key) + >>> 'Hello {name}, welcome to {location}'.format_map(PlaceholderDict()) + 'Hello <name>, welcome to <location>' + + (Suggested by Raymond Hettinger and implemented by Eric Smith in + :issue:`6081`.) + +* The interpreter can now be started with a quiet option, ``-q``, to prevent + the copyright and version information from being displayed in the interactive + mode. The option can be introspected using the :attr:`sys.flags` attribute:: + + $ python -q + >>> sys.flags + sys.flags(debug=0, division_warning=0, inspect=0, interactive=0, + optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, + ignore_environment=0, verbose=0, bytes_warning=0, quiet=1) + + (Contributed by Marcin Wojdyr in :issue:`1772833`). + +* The :func:`hasattr` function works by calling :func:`getattr` and detecting + whether an exception is raised. This technique allows it to detect methods + created dynamically by :meth:`__getattr__` or :meth:`__getattribute__` which + would otherwise be absent from the class dictionary. Formerly, *hasattr* + would catch any exception, possibly masking genuine errors. Now, *hasattr* + has been tightened to only catch :exc:`AttributeError` and let other + exceptions pass through:: + + >>> class A: + @property + def f(self): + return 1 // 0 + + >>> a = A() + >>> hasattr(a, 'f') + Traceback (most recent call last): + ... + ZeroDivisionError: integer division or modulo by zero + + (Discovered by Yury Selivanov and fixed by Benjamin Peterson; :issue:`9666`.) + +* The :func:`str` of a float or complex number is now the same as its + :func:`repr`. Previously, the :func:`str` form was shorter but that just + caused confusion and is no longer needed now that the shortest possible + :func:`repr` is displayed by default: + + >>> import math + >>> repr(math.pi) + '3.141592653589793' + >>> str(math.pi) + '3.141592653589793' + + (Proposed and implemented by Mark Dickinson; :issue:`9337`.) + +* :class:`memoryview` objects now have a :meth:`~memoryview.release()` method + and they also now support the context manager protocol. This allows timely + release of any resources that were acquired when requesting a buffer from the + original object. + + >>> with memoryview(b'abcdefgh') as v: + print(v.tolist()) + [97, 98, 99, 100, 101, 102, 103, 104] + + (Added by Antoine Pitrou; :issue:`9757`.) + +* Previously it was illegal to delete a name from the local namespace if it + occurs as a free variable in a nested block:: + + def outer(x): + def inner(): + return x + inner() + del x + + This is now allowed. Remember that the target of an :keyword:`except` clause + is cleared, so this code which used to work with Python 2.6, raised a + :exc:`SyntaxError` with Python 3.1 and now works again:: + + def f(): + def print_error(): + print(e) + try: + something + except Exception as e: + print_error() + # implicit "del e" here + + (See :issue:`4617`.) + +* The internal :c:type:`structsequence` tool now creates subclasses of tuple. + This means that C structures like those returned by :func:`os.stat`, + :func:`time.gmtime`, and :attr:`sys.version_info` now work like a + :term:`named tuple` and now work with functions and methods that + expect a tuple as an argument. This is a big step forward in making the C + structures as flexible as their pure Python counterparts: + + >>> isinstance(sys.version_info, tuple) + True + >>> 'Version %d.%d.%d %s(%d)' % sys.version_info + 'Version 3.2.0 final(0)' + + (Suggested by Arfrever Frehtes Taifersar Arahesis and implemented + by Benjamin Peterson in :issue:`8413`.) + +* Warnings are now easier to control using the :envvar:`PYTHONWARNINGS` + environment variable as an alternative to using ``-W`` at the command line:: + + $ export PYTHONWARNINGS='ignore::RuntimeWarning::,once::UnicodeWarning::' + + (Suggested by Barry Warsaw and implemented by Philip Jenvey in :issue:`7301`.) + +* A new warning category, :exc:`ResourceWarning`, has been added. It is + emitted when potential issues with resource consumption or cleanup + are detected. It is silenced by default in normal release builds but + can be enabled through the means provided by the :mod:`warnings` + module, or on the command line. + + A :exc:`ResourceWarning` is issued at interpreter shutdown if the + :data:`gc.garbage` list isn't empty, and if :attr:`gc.DEBUG_UNCOLLECTABLE` is + set, all uncollectable objects are printed. This is meant to make the + programmer aware that their code contains object finalization issues. + + A :exc:`ResourceWarning` is also issued when a :term:`file object` is destroyed + without having been explicitly closed. While the deallocator for such + object ensures it closes the underlying operating system resource + (usually, a file descriptor), the delay in deallocating the object could + produce various issues, especially under Windows. Here is an example + of enabling the warning from the command line:: + + $ python -q -Wdefault + >>> f = open("foo", "wb") + >>> del f + __main__:1: ResourceWarning: unclosed file <_io.BufferedWriter name='foo'> + + (Added by Antoine Pitrou and Georg Brandl in :issue:`10093` and :issue:`477863`.) + +* :class:`range` objects now support *index* and *count* methods. This is part + of an effort to make more objects fully implement the + :class:`collections.Sequence` :term:`abstract base class`. As a result, the + language will have a more uniform API. In addition, :class:`range` objects + now support slicing and negative indices, even with values larger than + :attr:`sys.maxsize`. This makes *range* more interoperable with lists:: + + >>> range(0, 100, 2).count(10) + 1 + >>> range(0, 100, 2).index(10) + 5 + >>> range(0, 100, 2)[5] + 10 + >>> range(0, 100, 2)[0:5] + range(0, 10, 2) + + (Contributed by Daniel Stutzbach in :issue:`9213`, by Alexander Belopolsky + in :issue:`2690`, and by Nick Coghlan in :issue:`10889`.) + +* The :func:`callable` builtin function from Py2.x was resurrected. It provides + a concise, readable alternative to using an :term:`abstract base class` in an + expression like ``isinstance(x, collections.Callable)``: + + >>> callable(max) + True + >>> callable(20) + False + + (See :issue:`10518`.) + +* Python's import mechanism can now load modules installed in directories with + non-ASCII characters in the path name. This solved an aggravating problem + with home directories for users with non-ASCII characters in their usernames. + + (Required extensive work by Victor Stinner in :issue:`9425`.) + + +New, Improved, and Deprecated Modules +===================================== + +Python's standard library has undergone significant maintenance efforts and +quality improvements. + +The biggest news for Python 3.2 is that the :mod:`email` package, :mod:`mailbox` +module, and :mod:`nntplib` modules now work correctly with the bytes/text model +in Python 3. For the first time, there is correct handling of messages with +mixed encodings. + +Throughout the standard library, there has been more careful attention to +encodings and text versus bytes issues. In particular, interactions with the +operating system are now better able to exchange non-ASCII data using the +Windows MBCS encoding, locale-aware encodings, or UTF-8. + +Another significant win is the addition of substantially better support for +*SSL* connections and security certificates. + +In addition, more classes now implement a :term:`context manager` to support +convenient and reliable resource clean-up using a :keyword:`with` statement. + +email +----- + +The usability of the :mod:`email` package in Python 3 has been mostly fixed by +the extensive efforts of R. David Murray. The problem was that emails are +typically read and stored in the form of :class:`bytes` rather than :class:`str` +text, and they may contain multiple encodings within a single email. So, the +email package had to be extended to parse and generate email messages in bytes +format. + +* New functions :func:`~email.message_from_bytes` and + :func:`~email.message_from_binary_file`, and new classes + :class:`~email.parser.BytesFeedParser` and :class:`~email.parser.BytesParser` + allow binary message data to be parsed into model objects. + +* Given bytes input to the model, :meth:`~email.message.Message.get_payload` + will by default decode a message body that has a + :mailheader:`Content-Transfer-Encoding` of *8bit* using the charset + specified in the MIME headers and return the resulting string. + +* Given bytes input to the model, :class:`~email.generator.Generator` will + convert message bodies that have a :mailheader:`Content-Transfer-Encoding` of + *8bit* to instead have a *7bit* :mailheader:`Content-Transfer-Encoding`. + + Headers with unencoded non-ASCII bytes are deemed to be :rfc:`2047`\ -encoded + using the *unknown-8bit* character set. + +* A new class :class:`~email.generator.BytesGenerator` produces bytes as output, + preserving any unchanged non-ASCII data that was present in the input used to + build the model, including message bodies with a + :mailheader:`Content-Transfer-Encoding` of *8bit*. + +* The :mod:`smtplib` :class:`~smtplib.SMTP` class now accepts a byte string + for the *msg* argument to the :meth:`~smtplib.SMTP.sendmail` method, + and a new method, :meth:`~smtplib.SMTP.send_message` accepts a + :class:`~email.message.Message` object and can optionally obtain the + *from_addr* and *to_addrs* addresses directly from the object. + +(Proposed and implemented by R. David Murray, :issue:`4661` and :issue:`10321`.) + +elementtree +----------- + +The :mod:`xml.etree.ElementTree` package and its :mod:`xml.etree.cElementTree` +counterpart have been updated to version 1.3. + +Several new and useful functions and methods have been added: + +* :func:`xml.etree.ElementTree.fromstringlist` which builds an XML document + from a sequence of fragments +* :func:`xml.etree.ElementTree.register_namespace` for registering a global + namespace prefix +* :func:`xml.etree.ElementTree.tostringlist` for string representation + including all sublists +* :meth:`xml.etree.ElementTree.Element.extend` for appending a sequence of zero + or more elements +* :meth:`xml.etree.ElementTree.Element.iterfind` searches an element and + subelements +* :meth:`xml.etree.ElementTree.Element.itertext` creates a text iterator over + an element and its subelements +* :meth:`xml.etree.ElementTree.TreeBuilder.end` closes the current element +* :meth:`xml.etree.ElementTree.TreeBuilder.doctype` handles a doctype + declaration + +Two methods have been deprecated: + +* :meth:`xml.etree.ElementTree.getchildren` use ``list(elem)`` instead. +* :meth:`xml.etree.ElementTree.getiterator` use ``Element.iter`` instead. + +For details of the update, see `Introducing ElementTree +<http://effbot.org/zone/elementtree-13-intro.htm>`_ on Fredrik Lundh's website. + +(Contributed by Florent Xicluna and Fredrik Lundh, :issue:`6472`.) + +functools +--------- + +* The :mod:`functools` module includes a new decorator for caching function + calls. :func:`functools.lru_cache` can save repeated queries to an external + resource whenever the results are expected to be the same. + + For example, adding a caching decorator to a database query function can save + database accesses for popular searches: + + >>> import functools + >>> @functools.lru_cache(maxsize=300) + >>> def get_phone_number(name): + c = conn.cursor() + c.execute('SELECT phonenumber FROM phonelist WHERE name=?', (name,)) + return c.fetchone()[0] + + >>> for name in user_requests: + get_phone_number(name) # cached lookup + + To help with choosing an effective cache size, the wrapped function is + instrumented for tracking cache statistics: + + >>> get_phone_number.cache_info() + CacheInfo(hits=4805, misses=980, maxsize=300, currsize=300) + + If the phonelist table gets updated, the outdated contents of the cache can be + cleared with: + + >>> get_phone_number.cache_clear() + + (Contributed by Raymond Hettinger and incorporating design ideas from Jim + Baker, Miki Tebeka, and Nick Coghlan; see `recipe 498245 + <http://code.activestate.com/recipes/498245>`_\, `recipe 577479 + <http://code.activestate.com/recipes/577479>`_\, :issue:`10586`, and + :issue:`10593`.) + +* The :func:`functools.wraps` decorator now adds a :attr:`__wrapped__` attribute + pointing to the original callable function. This allows wrapped functions to + be introspected. It also copies :attr:`__annotations__` if defined. And now + it also gracefully skips over missing attributes such as :attr:`__doc__` which + might not be defined for the wrapped callable. + + In the above example, the cache can be removed by recovering the original + function: + + >>> get_phone_number = get_phone_number.__wrapped__ # uncached function + + (By Nick Coghlan and Terrence Cole; :issue:`9567`, :issue:`3445`, and + :issue:`8814`.) + +* To help write classes with rich comparison methods, a new decorator + :func:`functools.total_ordering` will use a existing equality and inequality + methods to fill in the remaining methods. + + For example, supplying *__eq__* and *__lt__* will enable + :func:`~functools.total_ordering` to fill-in *__le__*, *__gt__* and *__ge__*:: + + @total_ordering + class Student: + def __eq__(self, other): + return ((self.lastname.lower(), self.firstname.lower()) == + (other.lastname.lower(), other.firstname.lower())) + def __lt__(self, other): + return ((self.lastname.lower(), self.firstname.lower()) < + (other.lastname.lower(), other.firstname.lower())) + + With the *total_ordering* decorator, the remaining comparison methods + are filled in automatically. + + (Contributed by Raymond Hettinger.) + +* To aid in porting programs from Python 2, the :func:`functools.cmp_to_key` + function converts an old-style comparison function to + modern :term:`key function`: + + >>> # locale-aware sort order + >>> sorted(iterable, key=cmp_to_key(locale.strcoll)) + + For sorting examples and a brief sorting tutorial, see the `Sorting HowTo + <http://wiki.python.org/moin/HowTo/Sorting/>`_ tutorial. + + (Contributed by Raymond Hettinger.) + +itertools +--------- + +* The :mod:`itertools` module has a new :func:`~itertools.accumulate` function + modeled on APL's *scan* operator and Numpy's *accumulate* function: + + >>> from itertools import accumulate + >>> list(accumulate([8, 2, 50])) + [8, 10, 60] + + >>> prob_dist = [0.1, 0.4, 0.2, 0.3] + >>> list(accumulate(prob_dist)) # cumulative probability distribution + [0.1, 0.5, 0.7, 1.0] + + For an example using :func:`~itertools.accumulate`, see the :ref:`examples for + the random module <random-examples>`. + + (Contributed by Raymond Hettinger and incorporating design suggestions + from Mark Dickinson.) + +collections +----------- + +* The :class:`collections.Counter` class now has two forms of in-place + subtraction, the existing *-=* operator for `saturating subtraction + <http://en.wikipedia.org/wiki/Saturation_arithmetic>`_ and the new + :meth:`~collections.Counter.subtract` method for regular subtraction. The + former is suitable for `multisets <http://en.wikipedia.org/wiki/Multiset>`_ + which only have positive counts, and the latter is more suitable for use cases + that allow negative counts: + + >>> tally = Counter(dogs=5, cat=3) + >>> tally -= Counter(dogs=2, cats=8) # saturating subtraction + >>> tally + Counter({'dogs': 3}) + + >>> tally = Counter(dogs=5, cats=3) + >>> tally.subtract(dogs=2, cats=8) # regular subtraction + >>> tally + Counter({'dogs': 3, 'cats': -5}) + + (Contributed by Raymond Hettinger.) + +* The :class:`collections.OrderedDict` class has a new method + :meth:`~collections.OrderedDict.move_to_end` which takes an existing key and + moves it to either the first or last position in the ordered sequence. + + The default is to move an item to the last position. This is equivalent of + renewing an entry with ``od[k] = od.pop(k)``. + + A fast move-to-end operation is useful for resequencing entries. For example, + an ordered dictionary can be used to track order of access by aging entries + from the oldest to the most recently accessed. + + >>> d = OrderedDict.fromkeys(['a', 'b', 'X', 'd', 'e']) + >>> list(d) + ['a', 'b', 'X', 'd', 'e'] + >>> d.move_to_end('X') + >>> list(d) + ['a', 'b', 'd', 'e', 'X'] + + (Contributed by Raymond Hettinger.) + +* The :class:`collections.deque` class grew two new methods + :meth:`~collections.deque.count` and :meth:`~collections.deque.reverse` that + make them more substitutable for :class:`list` objects: + + >>> d = deque('simsalabim') + >>> d.count('s') + 2 + >>> d.reverse() + >>> d + deque(['m', 'i', 'b', 'a', 'l', 'a', 's', 'm', 'i', 's']) + + (Contributed by Raymond Hettinger.) + +threading +--------- + +The :mod:`threading` module has a new :class:`~threading.Barrier` +synchronization class for making multiple threads wait until all of them have +reached a common barrier point. Barriers are useful for making sure that a task +with multiple preconditions does not run until all of the predecessor tasks are +complete. + +Barriers can work with an arbitrary number of threads. This is a generalization +of a `Rendezvous <http://en.wikipedia.org/wiki/Synchronous_rendezvous>`_ which +is defined for only two threads. + +Implemented as a two-phase cyclic barrier, :class:`~threading.Barrier` objects +are suitable for use in loops. The separate *filling* and *draining* phases +assure that all threads get released (drained) before any one of them can loop +back and re-enter the barrier. The barrier fully resets after each cycle. + +Example of using barriers:: + + from threading import Barrier, Thread + + def get_votes(site): + ballots = conduct_election(site) + all_polls_closed.wait() # do not count until all polls are closed + totals = summarize(ballots) + publish(site, totals) + + all_polls_closed = Barrier(len(sites)) + for site in sites: + Thread(target=get_votes, args=(site,)).start() + +In this example, the barrier enforces a rule that votes cannot be counted at any +polling site until all polls are closed. Notice how a solution with a barrier +is similar to one with :meth:`threading.Thread.join`, but the threads stay alive +and continue to do work (summarizing ballots) after the barrier point is +crossed. + +If any of the predecessor tasks can hang or be delayed, a barrier can be created +with an optional *timeout* parameter. Then if the timeout period elapses before +all the predecessor tasks reach the barrier point, all waiting threads are +released and a :exc:`~threading.BrokenBarrierError` exception is raised:: + + def get_votes(site): + ballots = conduct_election(site) + try: + all_polls_closed.wait(timeout = midnight - time.now()) + except BrokenBarrierError: + lockbox = seal_ballots(ballots) + queue.put(lockbox) + else: + totals = summarize(ballots) + publish(site, totals) + +In this example, the barrier enforces a more robust rule. If some election +sites do not finish before midnight, the barrier times-out and the ballots are +sealed and deposited in a queue for later handling. + +See `Barrier Synchronization Patterns +<http://parlab.eecs.berkeley.edu/wiki/_media/patterns/paraplop_g1_3.pdf>`_ for +more examples of how barriers can be used in parallel computing. Also, there is +a simple but thorough explanation of barriers in `The Little Book of Semaphores +<http://greenteapress.com/semaphores/downey08semaphores.pdf>`_, *section 3.6*. + +(Contributed by Kristján Valur Jónsson with an API review by Jeffrey Yasskin in +:issue:`8777`.) + +datetime and time +----------------- + +* The :mod:`datetime` module has a new type :class:`~datetime.timezone` that + implements the :class:`~datetime.tzinfo` interface by returning a fixed UTC + offset and timezone name. This makes it easier to create timezone-aware + datetime objects:: + + >>> from datetime import datetime, timezone + + >>> datetime.now(timezone.utc) + datetime.datetime(2010, 12, 8, 21, 4, 2, 923754, tzinfo=datetime.timezone.utc) + + >>> datetime.strptime("01/01/2000 12:00 +0000", "%m/%d/%Y %H:%M %z") + datetime.datetime(2000, 1, 1, 12, 0, tzinfo=datetime.timezone.utc) + +* Also, :class:`~datetime.timedelta` objects can now be multiplied by + :class:`float` and divided by :class:`float` and :class:`int` objects. + And :class:`~datetime.timedelta` objects can now divide one another. + +* The :meth:`datetime.date.strftime` method is no longer restricted to years + after 1900. The new supported year range is from 1000 to 9999 inclusive. + +* Whenever a two-digit year is used in a time tuple, the interpretation has been + governed by :attr:`time.accept2dyear`. The default is *True* which means that + for a two-digit year, the century is guessed according to the POSIX rules + governing the ``%y`` strptime format. + + Starting with Py3.2, use of the century guessing heuristic will emit a + :exc:`DeprecationWarning`. Instead, it is recommended that + :attr:`time.accept2dyear` be set to *False* so that large date ranges + can be used without guesswork:: + + >>> import time, warnings + >>> warnings.resetwarnings() # remove the default warning filters + + >>> time.accept2dyear = True # guess whether 11 means 11 or 2011 + >>> time.asctime((11, 1, 1, 12, 34, 56, 4, 1, 0)) + Warning (from warnings module): + ... + DeprecationWarning: Century info guessed for a 2-digit year. + 'Fri Jan 1 12:34:56 2011' + + >>> time.accept2dyear = False # use the full range of allowable dates + >>> time.asctime((11, 1, 1, 12, 34, 56, 4, 1, 0)) + 'Fri Jan 1 12:34:56 11' + + Several functions now have significantly expanded date ranges. When + :attr:`time.accept2dyear` is false, the :func:`time.asctime` function will + accept any year that fits in a C int, while the :func:`time.mktime` and + :func:`time.strftime` functions will accept the full range supported by the + corresponding operating system functions. + +(Contributed by Alexander Belopolsky and Victor Stinner in :issue:`1289118`, +:issue:`5094`, :issue:`6641`, :issue:`2706`, :issue:`1777412`, :issue:`8013`, +and :issue:`10827`.) + +.. XXX http://bugs.python.org/issue?%40search_text=datetime&%40sort=-activity + +math +---- + +The :mod:`math` module has been updated with six new functions inspired by the +C99 standard. + +The :func:`~math.isfinite` function provides a reliable and fast way to detect +special values. It returns *True* for regular numbers and *False* for *Nan* or +*Infinity*: + +>>> [isfinite(x) for x in (123, 4.56, float('Nan'), float('Inf'))] +[True, True, False, False] + +The :func:`~math.expm1` function computes ``e**x-1`` for small values of *x* +without incurring the loss of precision that usually accompanies the subtraction +of nearly equal quantities: + +>>> expm1(0.013671875) # more accurate way to compute e**x-1 for a small x +0.013765762467652909 + +The :func:`~math.erf` function computes a probability integral or `Gaussian +error function <http://en.wikipedia.org/wiki/Error_function>`_. The +complementary error function, :func:`~math.erfc`, is ``1 - erf(x)``: + +>>> erf(1.0/sqrt(2.0)) # portion of normal distribution within 1 standard deviation +0.682689492137086 +>>> erfc(1.0/sqrt(2.0)) # portion of normal distribution outside 1 standard deviation +0.31731050786291404 +>>> erf(1.0/sqrt(2.0)) + erfc(1.0/sqrt(2.0)) +1.0 + +The :func:`~math.gamma` function is a continuous extension of the factorial +function. See http://en.wikipedia.org/wiki/Gamma_function for details. Because +the function is related to factorials, it grows large even for small values of +*x*, so there is also a :func:`~math.lgamma` function for computing the natural +logarithm of the gamma function: + +>>> gamma(7.0) # six factorial +720.0 +>>> lgamma(801.0) # log(800 factorial) +4551.950730698041 + +(Contributed by Mark Dickinson.) + +abc +--- + +The :mod:`abc` module now supports :func:`~abc.abstractclassmethod` and +:func:`~abc.abstractstaticmethod`. + +These tools make it possible to define an :term:`abstract base class` that +requires a particular :func:`classmethod` or :func:`staticmethod` to be +implemented:: + + class Temperature(metaclass=abc.ABCMeta): + @abc.abstractclassmethod + def from_fahrenheit(cls, t): + ... + @abc.abstractclassmethod + def from_celsius(cls, t): + ... + +(Patch submitted by Daniel Urban; :issue:`5867`.) + +io +-- + +The :class:`io.BytesIO` has a new method, :meth:`~io.BytesIO.getbuffer`, which +provides functionality similar to :func:`memoryview`. It creates an editable +view of the data without making a copy. The buffer's random access and support +for slice notation are well-suited to in-place editing:: + + >>> REC_LEN, LOC_START, LOC_LEN = 34, 7, 11 + + >>> def change_location(buffer, record_number, location): + start = record_number * REC_LEN + LOC_START + buffer[start: start+LOC_LEN] = location + + >>> import io + + >>> byte_stream = io.BytesIO( + b'G3805 storeroom Main chassis ' + b'X7899 shipping Reserve cog ' + b'L6988 receiving Primary sprocket' + ) + >>> buffer = byte_stream.getbuffer() + >>> change_location(buffer, 1, b'warehouse ') + >>> change_location(buffer, 0, b'showroom ') + >>> print(byte_stream.getvalue()) + b'G3805 showroom Main chassis ' + b'X7899 warehouse Reserve cog ' + b'L6988 receiving Primary sprocket' + +(Contributed by Antoine Pitrou in :issue:`5506`.) + +reprlib +------- + +When writing a :meth:`__repr__` method for a custom container, it is easy to +forget to handle the case where a member refers back to the container itself. +Python's builtin objects such as :class:`list` and :class:`set` handle +self-reference by displaying "..." in the recursive part of the representation +string. + +To help write such :meth:`__repr__` methods, the :mod:`reprlib` module has a new +decorator, :func:`~reprlib.recursive_repr`, for detecting recursive calls to +:meth:`__repr__` and substituting a placeholder string instead:: + + >>> class MyList(list): + @recursive_repr() + def __repr__(self): + return '<' + '|'.join(map(repr, self)) + '>' + + >>> m = MyList('abc') + >>> m.append(m) + >>> m.append('x') + >>> print(m) + <'a'|'b'|'c'|...|'x'> + +(Contributed by Raymond Hettinger in :issue:`9826` and :issue:`9840`.) + +logging +------- + +In addition to dictionary-based configuration described above, the +:mod:`logging` package has many other improvements. + +The logging documentation has been augmented by a :ref:`basic tutorial +<logging-basic-tutorial>`\, an :ref:`advanced tutorial +<logging-advanced-tutorial>`\, and a :ref:`cookbook <logging-cookbook>` of +logging recipes. These documents are the fastest way to learn about logging. + +The :func:`logging.basicConfig` set-up function gained a *style* argument to +support three different types of string formatting. It defaults to "%" for +traditional %-formatting, can be set to "{" for the new :meth:`str.format` style, or +can be set to "$" for the shell-style formatting provided by +:class:`string.Template`. The following three configurations are equivalent:: + + >>> from logging import basicConfig + >>> basicConfig(style='%', format="%(name)s -> %(levelname)s: %(message)s") + >>> basicConfig(style='{', format="{name} -> {levelname} {message}") + >>> basicConfig(style='$', format="$name -> $levelname: $message") + +If no configuration is set-up before a logging event occurs, there is now a +default configuration using a :class:`~logging.StreamHandler` directed to +:attr:`sys.stderr` for events of ``WARNING`` level or higher. Formerly, an +event occurring before a configuration was set-up would either raise an +exception or silently drop the event depending on the value of +:attr:`logging.raiseExceptions`. The new default handler is stored in +:attr:`logging.lastResort`. + +The use of filters has been simplified. Instead of creating a +:class:`~logging.Filter` object, the predicate can be any Python callable that +returns *True* or *False*. + +There were a number of other improvements that add flexibility and simplify +configuration. See the module documentation for a full listing of changes in +Python 3.2. + +csv +--- + +The :mod:`csv` module now supports a new dialect, :class:`~csv.unix_dialect`, +which applies quoting for all fields and a traditional Unix style with ``'\n'`` as +the line terminator. The registered dialect name is ``unix``. + +The :class:`csv.DictWriter` has a new method, +:meth:`~csv.DictWriter.writeheader` for writing-out an initial row to document +the field names:: + + >>> import csv, sys + >>> w = csv.DictWriter(sys.stdout, ['name', 'dept'], dialect='unix') + >>> w.writeheader() + "name","dept" + >>> w.writerows([ + {'name': 'tom', 'dept': 'accounting'}, + {'name': 'susan', 'dept': 'Salesl'}]) + "tom","accounting" + "susan","sales" + +(New dialect suggested by Jay Talbot in :issue:`5975`, and the new method +suggested by Ed Abraham in :issue:`1537721`.) + +contextlib +---------- + +There is a new and slightly mind-blowing tool +:class:`~contextlib.ContextDecorator` that is helpful for creating a +:term:`context manager` that does double duty as a function decorator. + +As a convenience, this new functionality is used by +:func:`~contextlib.contextmanager` so that no extra effort is needed to support +both roles. + +The basic idea is that both context managers and function decorators can be used +for pre-action and post-action wrappers. Context managers wrap a group of +statements using a :keyword:`with` statement, and function decorators wrap a +group of statements enclosed in a function. So, occasionally there is a need to +write a pre-action or post-action wrapper that can be used in either role. + +For example, it is sometimes useful to wrap functions or groups of statements +with a logger that can track the time of entry and time of exit. Rather than +writing both a function decorator and a context manager for the task, the +:func:`~contextlib.contextmanager` provides both capabilities in a single +definition:: + + from contextlib import contextmanager + import logging + + logging.basicConfig(level=logging.INFO) + + @contextmanager + def track_entry_and_exit(name): + logging.info('Entering: {}'.format(name)) + yield + logging.info('Exiting: {}'.format(name)) + +Formerly, this would have only been usable as a context manager:: + + with track_entry_and_exit('widget loader'): + print('Some time consuming activity goes here') + load_widget() + +Now, it can be used as a decorator as well:: + + @track_entry_and_exit('widget loader') + def activity(): + print('Some time consuming activity goes here') + load_widget() + +Trying to fulfill two roles at once places some limitations on the technique. +Context managers normally have the flexibility to return an argument usable by +a :keyword:`with` statement, but there is no parallel for function decorators. + +In the above example, there is not a clean way for the *track_entry_and_exit* +context manager to return a logging instance for use in the body of enclosed +statements. + +(Contributed by Michael Foord in :issue:`9110`.) + +decimal and fractions +--------------------- + +Mark Dickinson crafted an elegant and efficient scheme for assuring that +different numeric datatypes will have the same hash value whenever their actual +values are equal (:issue:`8188`):: + + assert hash(Fraction(3, 2)) == hash(1.5) == \ + hash(Decimal("1.5")) == hash(complex(1.5, 0)) + +Some of the hashing details are exposed through a new attribute, +:attr:`sys.hash_info`, which describes the bit width of the hash value, the +prime modulus, the hash values for *infinity* and *nan*, and the multiplier +used for the imaginary part of a number: + +>>> sys.hash_info +sys.hash_info(width=64, modulus=2305843009213693951, inf=314159, nan=0, imag=1000003) + +An early decision to limit the inter-operability of various numeric types has +been relaxed. It is still unsupported (and ill-advised) to have implicit +mixing in arithmetic expressions such as ``Decimal('1.1') + float('1.1')`` +because the latter loses information in the process of constructing the binary +float. However, since existing floating point value can be converted losslessly +to either a decimal or rational representation, it makes sense to add them to +the constructor and to support mixed-type comparisons. + +* The :class:`decimal.Decimal` constructor now accepts :class:`float` objects + directly so there in no longer a need to use the :meth:`~decimal.Decimal.from_float` + method (:issue:`8257`). + +* Mixed type comparisons are now fully supported so that + :class:`~decimal.Decimal` objects can be directly compared with :class:`float` + and :class:`fractions.Fraction` (:issue:`2531` and :issue:`8188`). + +Similar changes were made to :class:`fractions.Fraction` so that the +:meth:`~fractions.Fraction.from_float()` and :meth:`~fractions.Fraction.from_decimal` +methods are no longer needed (:issue:`8294`): + +>>> Decimal(1.1) +Decimal('1.100000000000000088817841970012523233890533447265625') +>>> Fraction(1.1) +Fraction(2476979795053773, 2251799813685248) + +Another useful change for the :mod:`decimal` module is that the +:attr:`Context.clamp` attribute is now public. This is useful in creating +contexts that correspond to the decimal interchange formats specified in IEEE +754 (see :issue:`8540`). + +(Contributed by Mark Dickinson and Raymond Hettinger.) + +ftp +--- + +The :class:`ftplib.FTP` class now supports the context manager protocol to +unconditionally consume :exc:`socket.error` exceptions and to close the FTP +connection when done:: + + >>> from ftplib import FTP + >>> with FTP("ftp1.at.proftpd.org") as ftp: + ftp.login() + ftp.dir() + + '230 Anonymous login ok, restrictions apply.' + dr-xr-xr-x 9 ftp ftp 154 May 6 10:43 . + dr-xr-xr-x 9 ftp ftp 154 May 6 10:43 .. + dr-xr-xr-x 5 ftp ftp 4096 May 6 10:43 CentOS + dr-xr-xr-x 3 ftp ftp 18 Jul 10 2008 Fedora + +Other file-like objects such as :class:`mmap.mmap` and :func:`fileinput.input` +also grew auto-closing context managers:: + + with fileinput.input(files=('log1.txt', 'log2.txt')) as f: + for line in f: + process(line) + +(Contributed by Tarek Ziadé and Giampaolo Rodolà in :issue:`4972`, and +by Georg Brandl in :issue:`8046` and :issue:`1286`.) + +The :class:`~ftplib.FTP_TLS` class now accepts a *context* parameter, which is a +:class:`ssl.SSLContext` object allowing bundling SSL configuration options, +certificates and private keys into a single (potentially long-lived) structure. + +(Contributed by Giampaolo Rodolà; :issue:`8806`.) + +popen +----- + +The :func:`os.popen` and :func:`subprocess.Popen` functions now support +:keyword:`with` statements for auto-closing of the file descriptors. + +(Contributed by Antoine Pitrou and Brian Curtin in :issue:`7461` and +:issue:`10554`.) + +select +------ + +The :mod:`select` module now exposes a new, constant attribute, +:attr:`~select.PIPE_BUF`, which gives the minimum number of bytes which are +guaranteed not to block when :func:`select.select` says a pipe is ready +for writing. + +>>> import select +>>> select.PIPE_BUF +512 + +(Available on Unix systems. Patch by Sébastien Sablé in :issue:`9862`) + +gzip and zipfile +---------------- + +:class:`gzip.GzipFile` now implements the :class:`io.BufferedIOBase` +:term:`abstract base class` (except for ``truncate()``). It also has a +:meth:`~gzip.GzipFile.peek` method and supports unseekable as well as +zero-padded file objects. + +The :mod:`gzip` module also gains the :func:`~gzip.compress` and +:func:`~gzip.decompress` functions for easier in-memory compression and +decompression. Keep in mind that text needs to be encoded as :class:`bytes` +before compressing and decompressing: + +>>> s = 'Three shall be the number thou shalt count, ' +>>> s += 'and the number of the counting shall be three' +>>> b = s.encode() # convert to utf-8 +>>> len(b) +89 +>>> c = gzip.compress(b) +>>> len(c) +77 +>>> gzip.decompress(c).decode()[:42] # decompress and convert to text +'Three shall be the number thou shalt count,' + +(Contributed by Anand B. Pillai in :issue:`3488`; and by Antoine Pitrou, Nir +Aides and Brian Curtin in :issue:`9962`, :issue:`1675951`, :issue:`7471` and +:issue:`2846`.) + +Also, the :class:`zipfile.ZipExtFile` class was reworked internally to represent +files stored inside an archive. The new implementation is significantly faster +and can be wrapped in a :class:`io.BufferedReader` object for more speedups. It +also solves an issue where interleaved calls to *read* and *readline* gave the +wrong results. + +(Patch submitted by Nir Aides in :issue:`7610`.) + +tarfile +------- + +The :class:`~tarfile.TarFile` class can now be used as a context manager. In +addition, its :meth:`~tarfile.TarFile.add` method has a new option, *filter*, +that controls which files are added to the archive and allows the file metadata +to be edited. + +The new *filter* option replaces the older, less flexible *exclude* parameter +which is now deprecated. If specified, the optional *filter* parameter needs to +be a :term:`keyword argument`. The user-supplied filter function accepts a +:class:`~tarfile.TarInfo` object and returns an updated +:class:`~tarfile.TarInfo` object, or if it wants the file to be excluded, the +function can return *None*:: + + >>> import tarfile, glob + + >>> def myfilter(tarinfo): + if tarinfo.isfile(): # only save real files + tarinfo.uname = 'monty' # redact the user name + return tarinfo + + >>> with tarfile.open(name='myarchive.tar.gz', mode='w:gz') as tf: + for filename in glob.glob('*.txt'): + tf.add(filename, filter=myfilter) + tf.list() + -rw-r--r-- monty/501 902 2011-01-26 17:59:11 annotations.txt + -rw-r--r-- monty/501 123 2011-01-26 17:59:11 general_questions.txt + -rw-r--r-- monty/501 3514 2011-01-26 17:59:11 prion.txt + -rw-r--r-- monty/501 124 2011-01-26 17:59:11 py_todo.txt + -rw-r--r-- monty/501 1399 2011-01-26 17:59:11 semaphore_notes.txt + +(Proposed by Tarek Ziadé and implemented by Lars Gustäbel in :issue:`6856`.) + +hashlib +------- + +The :mod:`hashlib` module has two new constant attributes listing the hashing +algorithms guaranteed to be present in all implementations and those available +on the current implementation:: + + >>> import hashlib + + >>> hashlib.algorithms_guaranteed + {'sha1', 'sha224', 'sha384', 'sha256', 'sha512', 'md5'} + + >>> hashlib.algorithms_available + {'md2', 'SHA256', 'SHA512', 'dsaWithSHA', 'mdc2', 'SHA224', 'MD4', 'sha256', + 'sha512', 'ripemd160', 'SHA1', 'MDC2', 'SHA', 'SHA384', 'MD2', + 'ecdsa-with-SHA1','md4', 'md5', 'sha1', 'DSA-SHA', 'sha224', + 'dsaEncryption', 'DSA', 'RIPEMD160', 'sha', 'MD5', 'sha384'} + +(Suggested by Carl Chenet in :issue:`7418`.) + +ast +--- + +The :mod:`ast` module has a wonderful a general-purpose tool for safely +evaluating expression strings using the Python literal +syntax. The :func:`ast.literal_eval` function serves as a secure alternative to +the builtin :func:`eval` function which is easily abused. Python 3.2 adds +:class:`bytes` and :class:`set` literals to the list of supported types: +strings, bytes, numbers, tuples, lists, dicts, sets, booleans, and None. + +:: + + >>> from ast import literal_eval + + >>> request = "{'req': 3, 'func': 'pow', 'args': (2, 0.5)}" + >>> literal_eval(request) + {'args': (2, 0.5), 'req': 3, 'func': 'pow'} + + >>> request = "os.system('do something harmful')" + >>> literal_eval(request) + Traceback (most recent call last): + ... + ValueError: malformed node or string: <_ast.Call object at 0x101739a10> + +(Implemented by Benjamin Peterson and Georg Brandl.) + +os +-- + +Different operating systems use various encodings for filenames and environment +variables. The :mod:`os` module provides two new functions, +:func:`~os.fsencode` and :func:`~os.fsdecode`, for encoding and decoding +filenames: + +>>> filename = 'Sehenswürdigkeiten' +>>> os.fsencode(filename) +b'Sehensw\xc3\xbcrdigkeiten' + +Some operating systems allow direct access to encoded bytes in the +environment. If so, the :attr:`os.supports_bytes_environ` constant will be +true. + +For direct access to encoded environment variables (if available), +use the new :func:`os.getenvb` function or use :data:`os.environb` +which is a bytes version of :data:`os.environ`. + +(Contributed by Victor Stinner.) + +shutil +------ + +The :func:`shutil.copytree` function has two new options: + +* *ignore_dangling_symlinks*: when ``symlinks=False`` so that the function + copies a file pointed to by a symlink, not the symlink itself. This option + will silence the error raised if the file doesn't exist. + +* *copy_function*: is a callable that will be used to copy files. + :func:`shutil.copy2` is used by default. + +(Contributed by Tarek Ziadé.) + +In addition, the :mod:`shutil` module now supports :ref:`archiving operations +<archiving-operations>` for zipfiles, uncompressed tarfiles, gzipped tarfiles, +and bzipped tarfiles. And there are functions for registering additional +archiving file formats (such as xz compressed tarfiles or custom formats). + +The principal functions are :func:`~shutil.make_archive` and +:func:`~shutil.unpack_archive`. By default, both operate on the current +directory (which can be set by :func:`os.chdir`) and on any sub-directories. +The archive filename needs to be specified with a full pathname. The archiving +step is non-destructive (the original files are left unchanged). + +:: + + >>> import shutil, pprint + + >>> os.chdir('mydata') # change to the source directory + >>> f = shutil.make_archive('/var/backup/mydata', + 'zip') # archive the current directory + >>> f # show the name of archive + '/var/backup/mydata.zip' + >>> os.chdir('tmp') # change to an unpacking + >>> shutil.unpack_archive('/var/backup/mydata.zip') # recover the data + + >>> pprint.pprint(shutil.get_archive_formats()) # display known formats + [('bztar', "bzip2'ed tar-file"), + ('gztar', "gzip'ed tar-file"), + ('tar', 'uncompressed tar file'), + ('zip', 'ZIP file')] + + >>> shutil.register_archive_format( # register a new archive format + name = 'xz', + function = xz.compress, # callable archiving function + extra_args = [('level', 8)], # arguments to the function + description = 'xz compression' + ) + +(Contributed by Tarek Ziadé.) + +sqlite3 +------- + +The :mod:`sqlite3` module was updated to pysqlite version 2.6.0. It has two new capabilities. + +* The :attr:`sqlite3.Connection.in_transit` attribute is true if there is an + active transaction for uncommitted changes. + +* The :meth:`sqlite3.Connection.enable_load_extension` and + :meth:`sqlite3.Connection.load_extension` methods allows you to load SQLite + extensions from ".so" files. One well-known extension is the fulltext-search + extension distributed with SQLite. + +(Contributed by R. David Murray and Shashwat Anand; :issue:`8845`.) + +html +---- + +A new :mod:`html` module was introduced with only a single function, +:func:`~html.escape`, which is used for escaping reserved characters from HTML +markup: + +>>> import html +>>> html.escape('x > 2 && x < 7') +'x > 2 && x < 7' + +socket +------ + +The :mod:`socket` module has two new improvements. + +* Socket objects now have a :meth:`~socket.socket.detach()` method which puts + the socket into closed state without actually closing the underlying file + descriptor. The latter can then be reused for other purposes. + (Added by Antoine Pitrou; :issue:`8524`.) + +* :func:`socket.create_connection` now supports the context manager protocol + to unconditionally consume :exc:`socket.error` exceptions and to close the + socket when done. + (Contributed by Giampaolo Rodolà; :issue:`9794`.) + +ssl +--- + +The :mod:`ssl` module added a number of features to satisfy common requirements +for secure (encrypted, authenticated) internet connections: + +* A new class, :class:`~ssl.SSLContext`, serves as a container for persistent + SSL data, such as protocol settings, certificates, private keys, and various + other options. It includes a :meth:`~ssl.SSLContext.wrap_socket` for creating + an SSL socket from an SSL context. + +* A new function, :func:`ssl.match_hostname`, supports server identity + verification for higher-level protocols by implementing the rules of HTTPS + (from :rfc:`2818`) which are also suitable for other protocols. + +* The :func:`ssl.wrap_socket` constructor function now takes a *ciphers* + argument. The *ciphers* string lists the allowed encryption algorithms using + the format described in the `OpenSSL documentation + <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`__. + +* When linked against recent versions of OpenSSL, the :mod:`ssl` module now + supports the Server Name Indication extension to the TLS protocol, allowing + multiple "virtual hosts" using different certificates on a single IP port. + This extension is only supported in client mode, and is activated by passing + the *server_hostname* argument to :meth:`ssl.SSLContext.wrap_socket`. + +* Various options have been added to the :mod:`ssl` module, such as + :data:`~ssl.OP_NO_SSLv2` which disables the insecure and obsolete SSLv2 + protocol. + +* The extension now loads all the OpenSSL ciphers and digest algorithms. If + some SSL certificates cannot be verified, they are reported as an "unknown + algorithm" error. + +* The version of OpenSSL being used is now accessible using the module + attributes :data:`ssl.OPENSSL_VERSION` (a string), + :data:`ssl.OPENSSL_VERSION_INFO` (a 5-tuple), and + :data:`ssl.OPENSSL_VERSION_NUMBER` (an integer). + +(Contributed by Antoine Pitrou in :issue:`8850`, :issue:`1589`, :issue:`8322`, +:issue:`5639`, :issue:`4870`, :issue:`8484`, and :issue:`8321`.) + +nntp +---- + +The :mod:`nntplib` module has a revamped implementation with better bytes and +text semantics as well as more practical APIs. These improvements break +compatibility with the nntplib version in Python 3.1, which was partly +dysfunctional in itself. + +Support for secure connections through both implicit (using +:class:`nntplib.NNTP_SSL`) and explicit (using :meth:`nntplib.NNTP.starttls`) +TLS has also been added. + +(Contributed by Antoine Pitrou in :issue:`9360` and Andrew Vant in :issue:`1926`.) + +certificates +------------ + +:class:`http.client.HTTPSConnection`, :class:`urllib.request.HTTPSHandler` +and :func:`urllib.request.urlopen` now take optional arguments to allow for +server certificate checking against a set of Certificate Authorities, +as recommended in public uses of HTTPS. + +(Added by Antoine Pitrou, :issue:`9003`.) + +imaplib +------- + +Support for explicit TLS on standard IMAP4 connections has been added through +the new :mod:`imaplib.IMAP4.starttls` method. + +(Contributed by Lorenzo M. Catucci and Antoine Pitrou, :issue:`4471`.) + +http.client +----------- + +There were a number of small API improvements in the :mod:`http.client` module. +The old-style HTTP 0.9 simple responses are no longer supported and the *strict* +parameter is deprecated in all classes. + +The :class:`~http.client.HTTPConnection` and +:class:`~http.client.HTTPSConnection` classes now have a *source_address* +parameter for a (host, port) tuple indicating where the HTTP connection is made +from. + +Support for certificate checking and HTTPS virtual hosts were added to +:class:`~http.client.HTTPSConnection`. + +The :meth:`~http.client.HTTPConnection.request` method on connection objects +allowed an optional *body* argument so that a :term:`file object` could be used +to supply the content of the request. Conveniently, the *body* argument now +also accepts an :term:`iterable` object so long as it includes an explicit +``Content-Length`` header. This extended interface is much more flexible than +before. + +To establish an HTTPS connection through a proxy server, there is a new +:meth:`~http.client.HTTPConnection.set_tunnel` method that sets the host and +port for HTTP Connect tunneling. + +To match the behavior of :mod:`http.server`, the HTTP client library now also +encodes headers with ISO-8859-1 (Latin-1) encoding. It was already doing that +for incoming headers, so now the behavior is consistent for both incoming and +outgoing traffic. (See work by Armin Ronacher in :issue:`10980`.) + +unittest +-------- + +The unittest module has a number of improvements supporting test discovery for +packages, easier experimentation at the interactive prompt, new testcase +methods, improved diagnostic messages for test failures, and better method +names. + +* The command-line call ``python -m unittest`` can now accept file paths + instead of module names for running specific tests (:issue:`10620`). The new + test discovery can find tests within packages, locating any test importable + from the top-level directory. The top-level directory can be specified with + the `-t` option, a pattern for matching files with ``-p``, and a directory to + start discovery with ``-s``:: + + $ python -m unittest discover -s my_proj_dir -p _test.py + + (Contributed by Michael Foord.) + +* Experimentation at the interactive prompt is now easier because the + :class:`unittest.case.TestCase` class can now be instantiated without + arguments: + + >>> TestCase().assertEqual(pow(2, 3), 8) + + (Contributed by Michael Foord.) + +* The :mod:`unittest` module has two new methods, + :meth:`~unittest.TestCase.assertWarns` and + :meth:`~unittest.TestCase.assertWarnsRegex` to verify that a given warning type + is triggered by the code under test:: + + with self.assertWarns(DeprecationWarning): + legacy_function('XYZ') + + (Contributed by Antoine Pitrou, :issue:`9754`.) + + Another new method, :meth:`~unittest.TestCase.assertCountEqual` is used to + compare two iterables to determine if their element counts are equal (whether + the same elements are present with the same number of occurrences regardless + of order):: + + def test_anagram(self): + self.assertCountEqual('algorithm', 'logarithm') + + (Contributed by Raymond Hettinger.) + +* A principal feature of the unittest module is an effort to produce meaningful + diagnostics when a test fails. When possible, the failure is recorded along + with a diff of the output. This is especially helpful for analyzing log files + of failed test runs. However, since diffs can sometime be voluminous, there is + a new :attr:`~unittest.TestCase.maxDiff` attribute that sets maximum length of + diffs displayed. + +* In addition, the method names in the module have undergone a number of clean-ups. + + For example, :meth:`~unittest.TestCase.assertRegex` is the new name for + :meth:`~unittest.TestCase.assertRegexpMatches` which was misnamed because the + test uses :func:`re.search`, not :func:`re.match`. Other methods using + regular expressions are now named using short form "Regex" in preference to + "Regexp" -- this matches the names used in other unittest implementations, + matches Python's old name for the :mod:`re` module, and it has unambiguous + camel-casing. + + (Contributed by Raymond Hettinger and implemented by Ezio Melotti.) + +* To improve consistency, some long-standing method aliases are being + deprecated in favor of the preferred names: + + =============================== ============================== + Old Name Preferred Name + =============================== ============================== + :meth:`assert_` :meth:`.assertTrue` + :meth:`assertEquals` :meth:`.assertEqual` + :meth:`assertNotEquals` :meth:`.assertNotEqual` + :meth:`assertAlmostEquals` :meth:`.assertAlmostEqual` + :meth:`assertNotAlmostEquals` :meth:`.assertNotAlmostEqual` + =============================== ============================== + + Likewise, the ``TestCase.fail*`` methods deprecated in Python 3.1 are expected + to be removed in Python 3.3. Also see the :ref:`deprecated-aliases` section in + the :mod:`unittest` documentation. + + (Contributed by Ezio Melotti; :issue:`9424`.) + +* The :meth:`~unittest.TestCase.assertDictContainsSubset` method was deprecated + because it was misimplemented with the arguments in the wrong order. This + created hard-to-debug optical illusions where tests like + ``TestCase().assertDictContainsSubset({'a':1, 'b':2}, {'a':1})`` would fail. + + (Contributed by Raymond Hettinger.) + +random +------ + +The integer methods in the :mod:`random` module now do a better job of producing +uniform distributions. Previously, they computed selections with +``int(n*random())`` which had a slight bias whenever *n* was not a power of two. +Now, multiple selections are made from a range up to the next power of two and a +selection is kept only when it falls within the range ``0 <= x < n``. The +functions and methods affected are :func:`~random.randrange`, +:func:`~random.randint`, :func:`~random.choice`, :func:`~random.shuffle` and +:func:`~random.sample`. + +(Contributed by Raymond Hettinger; :issue:`9025`.) + +poplib +------ + +:class:`~poplib.POP3_SSL` class now accepts a *context* parameter, which is a +:class:`ssl.SSLContext` object allowing bundling SSL configuration options, +certificates and private keys into a single (potentially long-lived) +structure. + +(Contributed by Giampaolo Rodolà; :issue:`8807`.) + +asyncore +-------- + +:class:`asyncore.dispatcher` now provides a +:meth:`~asyncore.dispatcher.handle_accepted()` method +returning a `(sock, addr)` pair which is called when a connection has actually +been established with a new remote endpoint. This is supposed to be used as a +replacement for old :meth:`~asyncore.dispatcher.handle_accept()` and avoids +the user to call :meth:`~asyncore.dispatcher.accept()` directly. + +(Contributed by Giampaolo Rodolà; :issue:`6706`.) + +tempfile +-------- + +The :mod:`tempfile` module has a new context manager, +:class:`~tempfile.TemporaryDirectory` which provides easy deterministic +cleanup of temporary directories:: + + with tempfile.TemporaryDirectory() as tmpdirname: + print('created temporary dir:', tmpdirname) + +(Contributed by Neil Schemenauer and Nick Coghlan; :issue:`5178`.) + +inspect +------- + +* The :mod:`inspect` module has a new function + :func:`~inspect.getgeneratorstate` to easily identify the current state of a + generator-iterator:: + + >>> from inspect import getgeneratorstate + >>> def gen(): + yield 'demo' + >>> g = gen() + >>> getgeneratorstate(g) + 'GEN_CREATED' + >>> next(g) + 'demo' + >>> getgeneratorstate(g) + 'GEN_SUSPENDED' + >>> next(g, None) + >>> getgeneratorstate(g) + 'GEN_CLOSED' + + (Contributed by Rodolpho Eckhardt and Nick Coghlan, :issue:`10220`.) + +* To support lookups without the possibility of activating a dynamic attribute, + the :mod:`inspect` module has a new function, :func:`~inspect.getattr_static`. + Unlike :func:`hasattr`, this is a true read-only search, guaranteed not to + change state while it is searching:: + + >>> class A: + @property + def f(self): + print('Running') + return 10 + + >>> a = A() + >>> getattr(a, 'f') + Running + 10 + >>> inspect.getattr_static(a, 'f') + <property object at 0x1022bd788> + + (Contributed by Michael Foord.) + +pydoc +----- + +The :mod:`pydoc` module now provides a much-improved Web server interface, as +well as a new command-line option ``-b`` to automatically open a browser window +to display that server:: + + $ pydoc3.2 -b + +(Contributed by Ron Adam; :issue:`2001`.) + +dis +--- + +The :mod:`dis` module gained two new functions for inspecting code, +:func:`~dis.code_info` and :func:`~dis.show_code`. Both provide detailed code +object information for the supplied function, method, source code string or code +object. The former returns a string and the latter prints it:: + + >>> import dis, random + >>> dis.show_code(random.choice) + Name: choice + Filename: /Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/random.py + Argument count: 2 + Kw-only arguments: 0 + Number of locals: 3 + Stack size: 11 + Flags: OPTIMIZED, NEWLOCALS, NOFREE + Constants: + 0: 'Choose a random element from a non-empty sequence.' + 1: 'Cannot choose from an empty sequence' + Names: + 0: _randbelow + 1: len + 2: ValueError + 3: IndexError + Variable names: + 0: self + 1: seq + 2: i + +In addition, the :func:`~dis.dis` function now accepts string arguments +so that the common idiom ``dis(compile(s, '', 'eval'))`` can be shortened +to ``dis(s)``:: + + >>> dis('3*x+1 if x%2==1 else x//2') + 1 0 LOAD_NAME 0 (x) + 3 LOAD_CONST 0 (2) + 6 BINARY_MODULO + 7 LOAD_CONST 1 (1) + 10 COMPARE_OP 2 (==) + 13 POP_JUMP_IF_FALSE 28 + 16 LOAD_CONST 2 (3) + 19 LOAD_NAME 0 (x) + 22 BINARY_MULTIPLY + 23 LOAD_CONST 1 (1) + 26 BINARY_ADD + 27 RETURN_VALUE + >> 28 LOAD_NAME 0 (x) + 31 LOAD_CONST 0 (2) + 34 BINARY_FLOOR_DIVIDE + 35 RETURN_VALUE + +Taken together, these improvements make it easier to explore how CPython is +implemented and to see for yourself what the language syntax does +under-the-hood. + +(Contributed by Nick Coghlan in :issue:`9147`.) + +dbm +--- + +All database modules now support the :meth:`get` and :meth:`setdefault` methods. + +(Suggested by Ray Allen in :issue:`9523`.) + +ctypes +------ + +A new type, :class:`ctypes.c_ssize_t` represents the C :c:type:`ssize_t` datatype. + +site +---- + +The :mod:`site` module has three new functions useful for reporting on the +details of a given Python installation. + +* :func:`~site.getsitepackages` lists all global site-packages directories. + +* :func:`~site.getuserbase` reports on the user's base directory where data can + be stored. + +* :func:`~site.getusersitepackages` reveals the user-specific site-packages + directory path. + +:: + + >>> import site + >>> site.getsitepackages() + ['/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages', + '/Library/Frameworks/Python.framework/Versions/3.2/lib/site-python', + '/Library/Python/3.2/site-packages'] + >>> site.getuserbase() + '/Users/raymondhettinger/Library/Python/3.2' + >>> site.getusersitepackages() + '/Users/raymondhettinger/Library/Python/3.2/lib/python/site-packages' + +Conveniently, some of site's functionality is accessible directly from the +command-line:: + + $ python -m site --user-base + /Users/raymondhettinger/.local + $ python -m site --user-site + /Users/raymondhettinger/.local/lib/python3.2/site-packages + +(Contributed by Tarek Ziadé in :issue:`6693`.) + +sysconfig +--------- + +The new :mod:`sysconfig` module makes it straightforward to discover +installation paths and configuration variables that vary across platforms and +installations. + +The module offers access simple access functions for platform and version +information: + +* :func:`~sysconfig.get_platform` returning values like *linux-i586* or + *macosx-10.6-ppc*. +* :func:`~sysconfig.get_python_version` returns a Python version string + such as "3.2". + +It also provides access to the paths and variables corresponding to one of +seven named schemes used by :mod:`distutils`. Those include *posix_prefix*, +*posix_home*, *posix_user*, *nt*, *nt_user*, *os2*, *os2_home*: + +* :func:`~sysconfig.get_paths` makes a dictionary containing installation paths + for the current installation scheme. +* :func:`~sysconfig.get_config_vars` returns a dictionary of platform specific + variables. + +There is also a convenient command-line interface:: + + C:\Python32>python -m sysconfig + Platform: "win32" + Python version: "3.2" + Current installation scheme: "nt" + + Paths: + data = "C:\Python32" + include = "C:\Python32\Include" + platinclude = "C:\Python32\Include" + platlib = "C:\Python32\Lib\site-packages" + platstdlib = "C:\Python32\Lib" + purelib = "C:\Python32\Lib\site-packages" + scripts = "C:\Python32\Scripts" + stdlib = "C:\Python32\Lib" + + Variables: + BINDIR = "C:\Python32" + BINLIBDEST = "C:\Python32\Lib" + EXE = ".exe" + INCLUDEPY = "C:\Python32\Include" + LIBDEST = "C:\Python32\Lib" + SO = ".pyd" + VERSION = "32" + abiflags = "" + base = "C:\Python32" + exec_prefix = "C:\Python32" + platbase = "C:\Python32" + prefix = "C:\Python32" + projectbase = "C:\Python32" + py_version = "3.2" + py_version_nodot = "32" + py_version_short = "3.2" + srcdir = "C:\Python32" + userbase = "C:\Documents and Settings\Raymond\Application Data\Python" + +(Moved out of Distutils by Tarek Ziadé.) + +pdb +--- + +The :mod:`pdb` debugger module gained a number of usability improvements: + +* :file:`pdb.py` now has a ``-c`` option that executes commands as given in a + :file:`.pdbrc` script file. +* A :file:`.pdbrc` script file can contain ``continue`` and ``next`` commands + that continue debugging. +* The :class:`Pdb` class constructor now accepts a *nosigint* argument. +* New commands: ``l(list)``, ``ll(long list)`` and ``source`` for + listing source code. +* New commands: ``display`` and ``undisplay`` for showing or hiding + the value of an expression if it has changed. +* New command: ``interact`` for starting an interactive interpreter containing + the global and local names found in the current scope. +* Breakpoints can be cleared by breakpoint number. + +(Contributed by Georg Brandl, Antonio Cuni and Ilya Sandler.) + +configparser +------------ + +The :mod:`configparser` module was modified to improve usability and +predictability of the default parser and its supported INI syntax. The old +:class:`ConfigParser` class was removed in favor of :class:`SafeConfigParser` +which has in turn been renamed to :class:`~configparser.ConfigParser`. Support +for inline comments is now turned off by default and section or option +duplicates are not allowed in a single configuration source. + +Config parsers gained a new API based on the mapping protocol:: + + >>> parser = ConfigParser() + >>> parser.read_string(""" + [DEFAULT] + location = upper left + visible = yes + editable = no + color = blue + + [main] + title = Main Menu + color = green + + [options] + title = Options + """) + >>> parser['main']['color'] + 'green' + >>> parser['main']['editable'] + 'no' + >>> section = parser['options'] + >>> section['title'] + 'Options' + >>> section['title'] = 'Options (editable: %(editable)s)' + >>> section['title'] + 'Options (editable: no)' + +The new API is implemented on top of the classical API, so custom parser +subclasses should be able to use it without modifications. + +The INI file structure accepted by config parsers can now be customized. Users +can specify alternative option/value delimiters and comment prefixes, change the +name of the *DEFAULT* section or switch the interpolation syntax. + +There is support for pluggable interpolation including an additional interpolation +handler :class:`~configparser.ExtendedInterpolation`:: + + >>> parser = ConfigParser(interpolation=ExtendedInterpolation()) + >>> parser.read_dict({'buildout': {'directory': '/home/ambv/zope9'}, + 'custom': {'prefix': '/usr/local'}}) + >>> parser.read_string(""" + [buildout] + parts = + zope9 + instance + find-links = + ${buildout:directory}/downloads/dist + + [zope9] + recipe = plone.recipe.zope9install + location = /opt/zope + + [instance] + recipe = plone.recipe.zope9instance + zope9-location = ${zope9:location} + zope-conf = ${custom:prefix}/etc/zope.conf + """) + >>> parser['buildout']['find-links'] + '\n/home/ambv/zope9/downloads/dist' + >>> parser['instance']['zope-conf'] + '/usr/local/etc/zope.conf' + >>> instance = parser['instance'] + >>> instance['zope-conf'] + '/usr/local/etc/zope.conf' + >>> instance['zope9-location'] + '/opt/zope' + +A number of smaller features were also introduced, like support for specifying +encoding in read operations, specifying fallback values for get-functions, or +reading directly from dictionaries and strings. + +(All changes contributed by Łukasz Langa.) + +.. XXX consider showing a difflib example + +urllib.parse +------------ + +A number of usability improvements were made for the :mod:`urllib.parse` module. + +The :func:`~urllib.parse.urlparse` function now supports `IPv6 +<http://en.wikipedia.org/wiki/IPv6>`_ addresses as described in :rfc:`2732`: + + >>> import urllib.parse + >>> urllib.parse.urlparse('http://[dead:beef:cafe:5417:affe:8FA3:deaf:feed]/foo/') + ParseResult(scheme='http', + netloc='[dead:beef:cafe:5417:affe:8FA3:deaf:feed]', + path='/foo/', + params='', + query='', + fragment='') + +The :func:`~urllib.parse.urldefrag` function now returns a :term:`named tuple`:: + + >>> r = urllib.parse.urldefrag('http://python.org/about/#target') + >>> r + DefragResult(url='http://python.org/about/', fragment='target') + >>> r[0] + 'http://python.org/about/' + >>> r.fragment + 'target' + +And, the :func:`~urllib.parse.urlencode` function is now much more flexible, +accepting either a string or bytes type for the *query* argument. If it is a +string, then the *safe*, *encoding*, and *error* parameters are sent to +:func:`~urllib.parse.quote_plus` for encoding:: + + >>> urllib.parse.urlencode([ + ('type', 'telenovela'), + ('name', '¿Dónde Está Elisa?')], + encoding='latin-1') + 'type=telenovela&name=%BFD%F3nde+Est%E1+Elisa%3F' + +As detailed in :ref:`parsing-ascii-encoded-bytes`, all the :mod:`urllib.parse` +functions now accept ASCII-encoded byte strings as input, so long as they are +not mixed with regular strings. If ASCII-encoded byte strings are given as +parameters, the return types will also be an ASCII-encoded byte strings: + + >>> urllib.parse.urlparse(b'http://www.python.org:80/about/') + ParseResultBytes(scheme=b'http', netloc=b'www.python.org:80', + path=b'/about/', params=b'', query=b'', fragment=b'') + +(Work by Nick Coghlan, Dan Mahn, and Senthil Kumaran in :issue:`2987`, +:issue:`5468`, and :issue:`9873`.) + +mailbox +------- + +Thanks to a concerted effort by R. David Murray, the :mod:`mailbox` module has +been fixed for Python 3.2. The challenge was that mailbox had been originally +designed with a text interface, but email messages are best represented with +:class:`bytes` because various parts of a message may have different encodings. + +The solution harnessed the :mod:`email` package's binary support for parsing +arbitrary email messages. In addition, the solution required a number of API +changes. + +As expected, the :meth:`~mailbox.Mailbox.add` method for +:class:`mailbox.Mailbox` objects now accepts binary input. + +:class:`~io.StringIO` and text file input are deprecated. Also, string input +will fail early if non-ASCII characters are used. Previously it would fail when +the email was processed in a later step. + +There is also support for binary output. The :meth:`~mailbox.Mailbox.get_file` +method now returns a file in the binary mode (where it used to incorrectly set +the file to text-mode). There is also a new :meth:`~mailbox.Mailbox.get_bytes` +method that returns a :class:`bytes` representation of a message corresponding +to a given *key*. + +It is still possible to get non-binary output using the old API's +:meth:`~mailbox.Mailbox.get_string` method, but that approach +is not very useful. Instead, it is best to extract messages from +a :class:`~mailbox.Message` object or to load them from binary input. + +(Contributed by R. David Murray, with efforts from Steffen Daode Nurpmeso and an +initial patch by Victor Stinner in :issue:`9124`.) + +turtledemo +---------- + +The demonstration code for the :mod:`turtle` module was moved from the *Demo* +directory to main library. It includes over a dozen sample scripts with +lively displays. Being on :attr:`sys.path`, it can now be run directly +from the command-line:: + + $ python -m turtledemo + +(Moved from the Demo directory by Alexander Belopolsky in :issue:`10199`.) + +Multi-threading +=============== + +* The mechanism for serializing execution of concurrently running Python threads + (generally known as the :term:`GIL` or :term:`Global Interpreter Lock`) has + been rewritten. Among the objectives were more predictable switching + intervals and reduced overhead due to lock contention and the number of + ensuing system calls. The notion of a "check interval" to allow thread + switches has been abandoned and replaced by an absolute duration expressed in + seconds. This parameter is tunable through :func:`sys.setswitchinterval()`. + It currently defaults to 5 milliseconds. + + Additional details about the implementation can be read from a `python-dev + mailing-list message + <http://mail.python.org/pipermail/python-dev/2009-October/093321.html>`_ + (however, "priority requests" as exposed in this message have not been kept + for inclusion). + + (Contributed by Antoine Pitrou.) + +* Regular and recursive locks now accept an optional *timeout* argument to their + :meth:`~threading.Lock.acquire` method. (Contributed by Antoine Pitrou; + :issue:`7316`.) + +* Similarly, :meth:`threading.Semaphore.acquire` also gained a *timeout* + argument. (Contributed by Torsten Landschoff; :issue:`850728`.) + +* Regular and recursive lock acquisitions can now be interrupted by signals on + platforms using Pthreads. This means that Python programs that deadlock while + acquiring locks can be successfully killed by repeatedly sending SIGINT to the + process (by pressing :kbd:`Ctrl+C` in most shells). + (Contributed by Reid Kleckner; :issue:`8844`.) + + +Optimizations +============= + +A number of small performance enhancements have been added: + +* Python's peephole optimizer now recognizes patterns such ``x in {1, 2, 3}`` as + being a test for membership in a set of constants. The optimizer recasts the + :class:`set` as a :class:`frozenset` and stores the pre-built constant. + + Now that the speed penalty is gone, it is practical to start writing + membership tests using set-notation. This style is both semantically clear + and operationally fast:: + + extension = name.rpartition('.')[2] + if extension in {'xml', 'html', 'xhtml', 'css'}: + handle(name) + + (Patch and additional tests contributed by Dave Malcolm; :issue:`6690`). + +* Serializing and unserializing data using the :mod:`pickle` module is now + several times faster. + + (Contributed by Alexandre Vassalotti, Antoine Pitrou + and the Unladen Swallow team in :issue:`9410` and :issue:`3873`.) + +* The `Timsort algorithm <http://en.wikipedia.org/wiki/Timsort>`_ used in + :meth:`list.sort` and :func:`sorted` now runs faster and uses less memory + when called with a :term:`key function`. Previously, every element of + a list was wrapped with a temporary object that remembered the key value + associated with each element. Now, two arrays of keys and values are + sorted in parallel. This saves the memory consumed by the sort wrappers, + and it saves time lost to delegating comparisons. + + (Patch by Daniel Stutzbach in :issue:`9915`.) + +* JSON decoding performance is improved and memory consumption is reduced + whenever the same string is repeated for multiple keys. Also, JSON encoding + now uses the C speedups when the ``sort_keys`` argument is true. + + (Contributed by Antoine Pitrou in :issue:`7451` and by Raymond Hettinger and + Antoine Pitrou in :issue:`10314`.) + +* Recursive locks (created with the :func:`threading.RLock` API) now benefit + from a C implementation which makes them as fast as regular locks, and between + 10x and 15x faster than their previous pure Python implementation. + + (Contributed by Antoine Pitrou; :issue:`3001`.) + +* The fast-search algorithm in stringlib is now used by the :meth:`split`, + :meth:`splitlines` and :meth:`replace` methods on + :class:`bytes`, :class:`bytearray` and :class:`str` objects. Likewise, the + algorithm is also used by :meth:`rfind`, :meth:`rindex`, :meth:`rsplit` and + :meth:`rpartition`. + + (Patch by Florent Xicluna in :issue:`7622` and :issue:`7462`.) + + +* String to integer conversions now work two "digits" at a time, reducing the + number of division and modulo operations. + + (:issue:`6713` by Gawain Bolton, Mark Dickinson, and Victor Stinner.) + +There were several other minor optimizations. Set differencing now runs faster +when one operand is much larger than the other (patch by Andress Bennetts in +:issue:`8685`). The :meth:`array.repeat` method has a faster implementation +(:issue:`1569291` by Alexander Belopolsky). The :class:`BaseHTTPRequestHandler` +has more efficient buffering (:issue:`3709` by Andrew Schaaf). The +:func:`operator.attrgetter` function has been sped-up (:issue:`10160` by +Christos Georgiou). And :class:`ConfigParser` loads multi-line arguments a bit +faster (:issue:`7113` by Łukasz Langa). + + +Unicode +======= + +Python has been updated to `Unicode 6.0.0 +<http://unicode.org/versions/Unicode6.0.0/>`_. The update to the standard adds +over 2,000 new characters including `emoji <http://en.wikipedia.org/wiki/Emoji>`_ +symbols which are important for mobile phones. + +In addition, the updated standard has altered the character properties for two +Kannada characters (U+0CF1, U+0CF2) and one New Tai Lue numeric character +(U+19DA), making the former eligible for use in identifiers while disqualifying +the latter. For more information, see `Unicode Character Database Changes +<http://www.unicode.org/versions/Unicode6.0.0/#Database_Changes>`_. + + +Codecs +====== + +Support was added for *cp720* Arabic DOS encoding (:issue:`1616979`). + +MBCS encoding no longer ignores the error handler argument. In the default +strict mode, it raises an :exc:`UnicodeDecodeError` when it encounters an +undecodable byte sequence and an :exc:`UnicodeEncodeError` for an unencodable +character. + +The MBCS codec supports ``'strict'`` and ``'ignore'`` error handlers for +decoding, and ``'strict'`` and ``'replace'`` for encoding. + +To emulate Python3.1 MBCS encoding, select the ``'ignore'`` handler for decoding +and the ``'replace'`` handler for encoding. + +On Mac OS X, Python decodes command line arguments with ``'utf-8'`` rather than +the locale encoding. + +By default, :mod:`tarfile` uses ``'utf-8'`` encoding on Windows (instead of +``'mbcs'``) and the ``'surrogateescape'`` error handler on all operating +systems. + + +Documentation +============= + +The documentation continues to be improved. + +* A table of quick links has been added to the top of lengthy sections such as + :ref:`built-in-funcs`. In the case of :mod:`itertools`, the links are + accompanied by tables of cheatsheet-style summaries to provide an overview and + memory jog without having to read all of the docs. + +* In some cases, the pure Python source code can be a helpful adjunct to the + documentation, so now many modules now feature quick links to the latest + version of the source code. For example, the :mod:`functools` module + documentation has a quick link at the top labeled: + + **Source code** :source:`Lib/functools.py`. + + (Contributed by Raymond Hettinger; see + `rationale <http://rhettinger.wordpress.com/2011/01/28/open-your-source-more/>`_.) + +* The docs now contain more examples and recipes. In particular, :mod:`re` + module has an extensive section, :ref:`re-examples`. Likewise, the + :mod:`itertools` module continues to be updated with new + :ref:`itertools-recipes`. + +* The :mod:`datetime` module now has an auxiliary implementation in pure Python. + No functionality was changed. This just provides an easier-to-read alternate + implementation. + + (Contributed by Alexander Belopolsky in :issue:`9528`.) + +* The unmaintained :file:`Demo` directory has been removed. Some demos were + integrated into the documentation, some were moved to the :file:`Tools/demo` + directory, and others were removed altogether. + + (Contributed by Georg Brandl in :issue:`7962`.) + + +IDLE +==== + +* The format menu now has an option to clean source files by stripping + trailing whitespace. + + (Contributed by Raymond Hettinger; :issue:`5150`.) + +* IDLE on Mac OS X now works with both Carbon AquaTk and Cocoa AquaTk. + + (Contributed by Kevin Walzer, Ned Deily, and Ronald Oussoren; :issue:`6075`.) + +Code Repository +=============== + +In addition to the existing Subversion code repository at http://svn.python.org +there is now a `Mercurial <http://mercurial.selenic.com/>`_ repository at +http://hg.python.org/\. + +After the 3.2 release, there are plans to switch to Mercurial as the primary +repository. This distributed version control system should make it easier for +members of the community to create and share external changesets. See +:pep:`385` for details. + +To learn the new version control system, see the `tutorial by Joel +Spolsky <http://hginit.com>`_ or the `Guide to Mercurial Workflows +<http://mercurial.selenic.com/guide/>`_. + + +Build and C API Changes +======================= + +Changes to Python's build process and to the C API include: + +* The *idle*, *pydoc* and *2to3* scripts are now installed with a + version-specific suffix on ``make altinstall`` (:issue:`10679`). + +* The C functions that access the Unicode Database now accept and return + characters from the full Unicode range, even on narrow unicode builds + (Py_UNICODE_TOLOWER, Py_UNICODE_ISDECIMAL, and others). A visible difference + in Python is that :func:`unicodedata.numeric` now returns the correct value + for large code points, and :func:`repr` may consider more characters as + printable. + + (Reported by Bupjoe Lee and fixed by Amaury Forgeot D'Arc; :issue:`5127`.) + +* Computed gotos are now enabled by default on supported compilers (which are + detected by the configure script). They can still be disabled selectively by + specifying ``--without-computed-gotos``. + + (Contributed by Antoine Pitrou; :issue:`9203`.) + +* The option ``--with-wctype-functions`` was removed. The built-in unicode + database is now used for all functions. + + (Contributed by Amaury Forgeot D'Arc; :issue:`9210`.) + +* Hash values are now values of a new type, :c:type:`Py_hash_t`, which is + defined to be the same size as a pointer. Previously they were of type long, + which on some 64-bit operating systems is still only 32 bits long. As a + result of this fix, :class:`set` and :class:`dict` can now hold more than + ``2**32`` entries on builds with 64-bit pointers (previously, they could grow + to that size but their performance degraded catastrophically). + + (Suggested by Raymond Hettinger and implemented by Benjamin Peterson; + :issue:`9778`.) + +* A new macro :c:macro:`Py_VA_COPY` copies the state of the variable argument + list. It is equivalent to C99 *va_copy* but available on all Python platforms + (:issue:`2443`). + +* A new C API function :c:func:`PySys_SetArgvEx` allows an embedded interpreter + to set :attr:`sys.argv` without also modifying :attr:`sys.path` + (:issue:`5753`). + +* :c:macro:`PyEval_CallObject` is now only available in macro form. The + function declaration, which was kept for backwards compatibility reasons, is + now removed -- the macro was introduced in 1997 (:issue:`8276`). + +* There is a new function :c:func:`PyLong_AsLongLongAndOverflow` which + is analogous to :c:func:`PyLong_AsLongAndOverflow`. They both serve to + convert Python :class:`int` into a native fixed-width type while providing + detection of cases where the conversion won't fit (:issue:`7767`). + +* The :c:func:`PyUnicode_CompareWithASCIIString` function now returns *not + equal* if the Python string is *NUL* terminated. + +* There is a new function :c:func:`PyErr_NewExceptionWithDoc` that is + like :c:func:`PyErr_NewException` but allows a docstring to be specified. + This lets C exceptions have the same self-documenting capabilities as + their pure Python counterparts (:issue:`7033`). + +* When compiled with the ``--with-valgrind`` option, the pymalloc + allocator will be automatically disabled when running under Valgrind. This + gives improved memory leak detection when running under Valgrind, while taking + advantage of pymalloc at other times (:issue:`2422`). + +* Removed the ``O?`` format from the *PyArg_Parse* functions. The format is no + longer used and it had never been documented (:issue:`8837`). + +There were a number of other small changes to the C-API. See the +:source:`Misc/NEWS` file for a complete list. + +Also, there were a number of updates to the Mac OS X build, see +:source:`Mac/BuildScript/README.txt` for details. For users running a 32/64-bit +build, there is a known problem with the default Tcl/Tk on Mac OS X 10.6. +Accordingly, we recommend installing an updated alternative such as +`ActiveState Tcl/Tk 8.5.9 <http://www.activestate.com/activetcl/downloads>`_\. +See http://www.python.org/download/mac/tcltk/ for additional details. + +Porting to Python 3.2 +===================== + +This section lists previously described changes and other bugfixes that may +require changes to your code: + +* The :mod:`configparser` module has a number of clean-ups. The major change is + to replace the old :class:`ConfigParser` class with long-standing preferred + alternative :class:`SafeConfigParser`. In addition there are a number of + smaller incompatibilities: + + * The interpolation syntax is now validated on + :meth:`~configparser.ConfigParser.get` and + :meth:`~configparser.ConfigParser.set` operations. In the default + interpolation scheme, only two tokens with percent signs are valid: ``%(name)s`` + and ``%%``, the latter being an escaped percent sign. + + * The :meth:`~configparser.ConfigParser.set` and + :meth:`~configparser.ConfigParser.add_section` methods now verify that + values are actual strings. Formerly, unsupported types could be introduced + unintentionally. + + * Duplicate sections or options from a single source now raise either + :exc:`~configparser.DuplicateSectionError` or + :exc:`~configparser.DuplicateOptionError`. Formerly, duplicates would + silently overwrite a previous entry. + + * Inline comments are now disabled by default so now the **;** character + can be safely used in values. + + * Comments now can be indented. Consequently, for **;** or **#** to appear at + the start of a line in multiline values, it has to be interpolated. This + keeps comment prefix characters in values from being mistaken as comments. + + * ``""`` is now a valid value and is no longer automatically converted to an + empty string. For empty strings, use ``"option ="`` in a line. + +* The :mod:`nntplib` module was reworked extensively, meaning that its APIs + are often incompatible with the 3.1 APIs. + +* :class:`bytearray` objects can no longer be used as filenames; instead, + they should be converted to :class:`bytes`. + +* The :meth:`array.tostring` and :meth:`array.fromstring` have been renamed to + :meth:`array.tobytes` and :meth:`array.frombytes` for clarity. The old names + have been deprecated. (See :issue:`8990`.) + +* ``PyArg_Parse*()`` functions: + + * "t#" format has been removed: use "s#" or "s*" instead + * "w" and "w#" formats has been removed: use "w*" instead + +* The :c:type:`PyCObject` type, deprecated in 3.1, has been removed. To wrap + opaque C pointers in Python objects, the :c:type:`PyCapsule` API should be used + instead; the new type has a well-defined interface for passing typing safety + information and a less complicated signature for calling a destructor. + +* The :func:`sys.setfilesystemencoding` function was removed because + it had a flawed design. + +* The :func:`random.seed` function and method now salt string seeds with an + sha512 hash function. To access the previous version of *seed* in order to + reproduce Python 3.1 sequences, set the *version* argument to *1*, + ``random.seed(s, version=1)``. + +* The previously deprecated :func:`string.maketrans` function has been removed + in favor of the static methods :meth:`bytes.maketrans` and + :meth:`bytearray.maketrans`. This change solves the confusion around which + types were supported by the :mod:`string` module. Now, :class:`str`, + :class:`bytes`, and :class:`bytearray` each have their own **maketrans** and + **translate** methods with intermediate translation tables of the appropriate + type. + + (Contributed by Georg Brandl; :issue:`5675`.) + +* The previously deprecated :func:`contextlib.nested` function has been removed + in favor of a plain :keyword:`with` statement which can accept multiple + context managers. The latter technique is faster (because it is built-in), + and it does a better job finalizing multiple context managers when one of them + raises an exception:: + + with open('mylog.txt') as infile, open('a.out', 'w') as outfile: + for line in infile: + if '<critical>' in line: + outfile.write(line) + + (Contributed by Georg Brandl and Mattias Brändström; + `appspot issue 53094 <http://codereview.appspot.com/53094>`_.) + +* :func:`struct.pack` now only allows bytes for the ``s`` string pack code. + Formerly, it would accept text arguments and implicitly encode them to bytes + using UTF-8. This was problematic because it made assumptions about the + correct encoding and because a variable-length encoding can fail when writing + to fixed length segment of a structure. + + Code such as ``struct.pack('<6sHHBBB', 'GIF87a', x, y)`` should be rewritten + with to use bytes instead of text, ``struct.pack('<6sHHBBB', b'GIF87a', x, y)``. + + (Discovered by David Beazley and fixed by Victor Stinner; :issue:`10783`.) + +* The :class:`xml.etree.ElementTree` class now raises an + :exc:`xml.etree.ElementTree.ParseError` when a parse fails. Previously it + raised a :exc:`xml.parsers.expat.ExpatError`. + +* The new, longer :func:`str` value on floats may break doctests which rely on + the old output format. + +* In :class:`subprocess.Popen`, the default value for *close_fds* is now + ``True`` under Unix; under Windows, it is ``True`` if the three standard + streams are set to ``None``, ``False`` otherwise. Previously, *close_fds* + was always ``False`` by default, which produced difficult to solve bugs + or race conditions when open file descriptors would leak into the child + process. + +* Support for legacy HTTP 0.9 has been removed from :mod:`urllib.request` + and :mod:`http.client`. Such support is still present on the server side + (in :mod:`http.server`). + + (Contributed by Antoine Pitrou, :issue:`10711`.) + +* SSL sockets in timeout mode now raise :exc:`socket.timeout` when a timeout + occurs, rather than a generic :exc:`~ssl.SSLError`. + + (Contributed by Antoine Pitrou, :issue:`10272`.) + +* The misleading functions :c:func:`PyEval_AcquireLock()` and + :c:func:`PyEval_ReleaseLock()` have been officially deprecated. The + thread-state aware APIs (such as :c:func:`PyEval_SaveThread()` + and :c:func:`PyEval_RestoreThread()`) should be used instead. + +* Due to security risks, :func:`asyncore.handle_accept` has been deprecated, and + a new function, :func:`asyncore.handle_accepted`, was added to replace it. + + (Contributed by Giampaolo Rodola in :issue:`6706`.) + +* Due to the new :term:`GIL` implementation, :c:func:`PyEval_InitThreads()` + cannot be called before :c:func:`Py_Initialize()` anymore. + |