522 lines
20 KiB
ReStructuredText
522 lines
20 KiB
ReStructuredText
****************************
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What's New In Python 3.2
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****************************
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:Author: Raymond Hettinger
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:Release: |release|
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:Date: |today|
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.. $Id$
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Rules for maintenance:
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* Anyone can add text to this document. Do not spend very much time
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on the wording of your changes, because your text will probably
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get rewritten to some degree.
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* The maintainer will go through Misc/NEWS periodically and add
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changes; it's therefore more important to add your changes to
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Misc/NEWS than to this file.
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* This is not a complete list of every single change; completeness
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is the purpose of Misc/NEWS. Some changes I consider too small
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or esoteric to include. If such a change is added to the text,
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I'll just remove it. (This is another reason you shouldn't spend
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too much time on writing your addition.)
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* If you want to draw your new text to the attention of the
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maintainer, add 'XXX' to the beginning of the paragraph or
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section.
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* It's OK to just add a fragmentary note about a change. For
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example: "XXX Describe the transmogrify() function added to the
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socket module." The maintainer will research the change and
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write the necessary text.
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* You can comment out your additions if you like, but it's not
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necessary (especially when a final release is some months away).
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* Credit the author of a patch or bugfix. Just the name is
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sufficient; the e-mail address isn't necessary. It's helpful to
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add the issue number:
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XXX Describe the transmogrify() function added to the socket
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module.
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(Contributed by P.Y. Developer; :issue:`12345`.)
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This saves the maintainer the effort of going through the SVN log
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when researching a change.
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This article explains the new features in Python 3.2, compared to 3.1.
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PEP 391: Dictionary Based Configuration for Logging
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====================================================
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The :mod:`logging` module provided two kinds of configuration, one style with
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function calls for each option or another style driven by an external file saved
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in a :mod:`ConfigParser` format. Those options did not provide the flexibility
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to create configurations from JSON or YAML files, nor did they support
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incremental configuration, which is needed for specifying logger options from a
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command line.
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To support a more flexible style, the module now offers
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:func:`logging.config.dictConfig` for specifying logging configuration with
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plain Python dictionaries. The configuration options include formatters,
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handlers, filters, and loggers. Here's a working example of a configuration
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dictionary::
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{"version": 1,
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"formatters": {"brief": {"format": "%(levelname)-8s: %(name)-15s: %(message)s"},
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"full": {"format": "%(asctime)s %(name)-15s %(levelname)-8s %(message)s"},
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},
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"handlers": {"console": {
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"class": "logging.StreamHandler",
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"formatter": "brief",
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"level": "INFO",
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"stream": "ext://sys.stdout"},
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"console_priority": {
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"class": "logging.StreamHandler",
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"formatter": "full",
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"level": "ERROR",
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"stream": "ext://sys.stderr"},
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},
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"root": {"level": "DEBUG", "handlers": ["console", "console_priority"]}}
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If that dictionary is stored in a file called "conf.json", it can loaded
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and called with code like this::
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>>> import logging.config
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>>> logging.config.dictConfig(json.load(open('conf.json', 'rb')))
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>>> logging.info("Transaction completed normally")
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>>> logging.critical("Abnormal termination")
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.. seealso::
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:pep:`391` - Dictionary Based Configuration for Logging
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PEP written by Vinay Sajip.
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PEP 3147: PYC Repository Directories
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=====================================
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Python's scheme for caching bytecode in *.pyc* files did not work well in
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environments with multiple python interpreters. If one interpreter encountered
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a cached file created by another interpreter, it would recompile the source and
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overwrite the cached file, thus losing the benefits of caching.
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The issue of "pyc fights" has become more pronounced as it has become
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commonplace for Linux distributions to ship with multiple versions of Python.
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These conflicts also arise with CPython alternatives such as Unladen Swallow.
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To solve this problem, Python's import machinery has been extended to use
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distinct filenames for each interpreter. Instead of Python 3.2 and Python 3.3 and
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Unladen Swallow each competing for a file called "mymodule.pyc", they will now
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look for "mymodule.cpython-32.pyc", "mymodule.cpython-33.pyc", and
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"mymodule.unladen10.pyc". And to prevent all of these new files from
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cluttering source directories, the *pyc* files are now collected in a
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"__pycache__" directory stored under the package directory.
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Aside from the filenames and target directories, the new scheme has a few
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aspects that are visible to the programmer:
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* Imported modules now have a :attr:`__cached__` attribute which stores the name
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of the actual file that was imported:
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>>> import collections
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>>> collections.__cached__
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'c:/py32/lib/__pycache__/collections.cpython-32.pyc'
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* The tag that is unique to each interpreter is accessible from the :mod:`imp`
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module:
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>>> import imp
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>>> imp.get_tag()
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'cpython-32'
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* Scripts that try to deduce source filename from the imported file now need to
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be smarter. It is no longer sufficient to simply strip the "c" from a ".pyc"
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filename. Instead, use the new functions in the :mod:`imp` module:
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>>> imp.source_from_cache('c:/py32/lib/__pycache__/collections.cpython-32.pyc')
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'c:/py32/lib/collections.py'
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>>> imp.cache_from_source('c:/py32/lib/collections.py')
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'c:/py32/lib/__pycache__/collections.cpython-32.pyc'
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* The :mod:`py_compile` and :mod:`compileall` modules have been updated to
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reflect the new naming convention and target directory.
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.. seealso::
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:pep:`3147` - PYC Repository Directories
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PEP written by Barry Warsaw.
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PEP 3149 ABI Version Tagged .so Files
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=====================================
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The PYC repository directory allows multiple bytecode cache files to be
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co-located. This PEP implements a similar mechanism for shared object files by
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giving them a common directory and distinct names for each version.
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The common directory is "pyshared" and the file names are made distinct by
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identifying the Python implementation (such as CPython, PyPy, Jython, etc.), the
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major and minor version numbers, and optional build flags (such as "d" for
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debug, "m" for pymalloc, "u" for wide-unicode). For an arbitrary package "foo",
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you may see these files when the distribution package is installed::
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/usr/share/pyshared/foo.cpython-32m.so
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/usr/share/pyshared/foo.cpython-33md.so
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In Python itself, the tags are accessible from functions in the :mod:`sysconfig`
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module::
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>>> import sysconfig
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>>> sysconfig.get_config_var('SOABI') # find the version tag
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'cpython-32mu'
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>>> sysconfig.get_config_var('SO') # find the full filename extension
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'cpython-32mu.so'
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.. seealso::
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:pep:`3149` - ABI Version Tagged .so Files
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PEP written by Barry Warsaw.
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Other Language Changes
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======================
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Some smaller changes made to the core Python language are:
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* The :func:`hasattr` function used to catch and suppress any Exception. Now,
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it only catches :exc:`AttributeError`. Under the hood, :func:`hasattr` works
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by calling :func:`getattr` and throwing away the results. This is necessary
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because dynamic attribute creation is possible using :meth:`__getattribute__`
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or :meth:`__getattr__`. If :func:`hasattr` were to just scan instance and class
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dictionaries it would miss the dynamic methods and make it difficult to
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implement proxy objects.
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(Discovered by Yury Selivanov and fixed by Benjamin Peterson; :issue:`9666`.)
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* The :func:`str` of a float or complex number is now the same as its
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:func:`repr`. Previously, the :func:`str` form was shorter but that just
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caused confusion and is no longer needed now that the shortest possible
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:func:`repr` is displayed by default:
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>>> repr(math.pi)
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'3.141592653589793'
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>>> str(math.pi)
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'3.141592653589793'
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(Proposed and implemented by Mark Dickinson; :issue:`9337`.)
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* The :func:`functools.wraps` decorator now adds a :attr:`__wrapped__` attribute
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pointing to the original callable function. This allows wrapped functions to
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be introspected. It also copies :attr:`__annotations__` if defined. And now
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it also gracefully skips over missing attributes such as :attr:`__doc__` which
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might not be defined for the wrapped callable.
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(By Nick Coghlan and Terrence Cole; :issue:`9567`, :issue:`3445`, and
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:issue:`8814`.)
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* The :mod:`abc` module now supports :func:`~abc.abstractclassmethod` and
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:func:`~abc.abstractstaticmethod`.
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(Patch submitted by Daniel Urban; :issue:`5867`.)
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* A warning message will now get printed at interpreter shutdown if the
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:data:`gc.garbage` list isn't empty. This is meant to make the programmer
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aware that their code contains object finalization issues.
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(Added by Antoine Pitrou; :issue:`477863`.)
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* Mark Dickinson crafted an elegant and efficient scheme for assuring that
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different numeric datatypes will have the same hash value whenever their
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actual values are equal::
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>>> assert hash(Fraction(3, 2)) == hash(1.5) == \
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hash(Decimal("1.5")) == hash(complex(1.5, 0))
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(See :issue:`8188`.)
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New, Improved, and Deprecated Modules
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=====================================
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* XXX mention :mod:`argparse`.
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* The :mod:`functools` module includes a new decorator for caching function
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calls. :func:`functools.lru_cache` can save repeated queries to an external
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resource whenever the results are expected to be the same.
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For example, adding a caching decorator to a database query function can save
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database accesses for popular searches::
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@functools.lru_cache(maxsize=300)
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def get_phone_number(name):
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c = conn.cursor()
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c.execute('SELECT phonenumber FROM phonelist WHERE name=?', (name,))
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return c.fetchone()[0]
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To help with choosing an effective cache size, the wrapped function is
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instrumented with two attributes *cache_hits* and *cache_misses*:
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>>> for name in user_requests:
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... get_phone_number(name)
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>>> print(get_phone_number.cache_hits, get_phone_number.cache_misses)
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4805 980
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If the phonelist table gets updated, the outdated contents of the cache can be
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cleared with:
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>>> get_phone_number.cache_clear()
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(Contributed by Raymond Hettinger.)
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* The previously deprecated :func:`contextlib.nested` function has been removed
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in favor of a plain :keyword:`with` statement which can accept multiple
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context managers. The latter technique is faster (because it is built-in),
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and it does a better job finalizing multiple context managers when one of them
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raises an exception.
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(Contributed by Georg Brandl and Mattias Brändström;
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`appspot issue 53094 <http://codereview.appspot.com/53094>`_.)
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* The :class:`ftplib.FTP` class now supports the context manager protocol to
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unconditionally consume :exc:`socket.error` exceptions and to close the FTP
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connection when done::
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>>> from ftplib import FTP
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>>> with FTP("ftp1.at.proftpd.org") as ftp:
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... ftp.login()
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... ftp.dir()
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...
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'230 Anonymous login ok, restrictions apply.'
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dr-xr-xr-x 9 ftp ftp 154 May 6 10:43 .
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dr-xr-xr-x 9 ftp ftp 154 May 6 10:43 ..
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dr-xr-xr-x 5 ftp ftp 4096 May 6 10:43 CentOS
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dr-xr-xr-x 3 ftp ftp 18 Jul 10 2008 Fedora
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Other file-like objects such as :class:`mmap.mmap` and :func:`fileinput.input`
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also grew auto-closing context managers::
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with fileinput.input(files=('log1.txt', 'log2.txt')) as f:
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for line in f:
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process(line)
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(Contributed by Tarek Ziadé and Giampaolo Rodolà in :issue:`4972`, and
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by Georg Brandl in :issue:`8046` and :issue:`1286`.)
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* The :mod:`os` module now has the :const:`ST_RDONLY` and :const:`ST_NOSUID`
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constants, for use with the :func:`~os.statvfs` function.
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(Patch by Adam Jackson; :issue:`7647`.)
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* :func:`os.getppid` is now supported on Windows. Note that it will continue to
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return the same pid even after the parent process has exited.
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(Patch by Jon Anglin; :issue:`6394`.)
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* The :func:`shutil.copytree` function has two new options:
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* *ignore_dangling_symlinks*: when ``symlinks=False`` so that the function
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copies the file pointed to by the symlink, not the symlink itself. This
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option will silence the error raised if the file doesn't exist.
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* *copy_function*: is a callable that will be used to copy files.
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:func:`shutil.copy2` is used by default.
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(Contributed by Tarek Ziadé.)
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* Socket objects now have a :meth:`~socket.socket.detach()` method which puts
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the socket into closed state without actually closing the underlying file
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descriptor. The latter can then be reused for other purposes.
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(Added by Antoine Pitrou; :issue:`8524`.)
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* The :mod:`sqlite3` module has two new capabilities.
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The :attr:`Connection.in_transit` attribute is true if there is an active
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transaction for uncommitted changes.
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The :meth:`Connection.enable_load_extension` and
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:meth:`Connection.load_extension` methods allows you to load SQLite extensions
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from ".so" files. One well-known extension is the fulltext-search extension
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distributed with SQLite.
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(Contributed by R. David Murray and Shashwat Anand; :issue:`8845`.)
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* The :mod:`ssl` module has a new class, :class:`~ssl.SSLContext` which serves
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as a container for various persistent SSL data, such as protocol settings,
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certificates, private keys, and various other options. The
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:meth:`~ssl.SSLContext.wrap_socket` method allows to create an SSL socket from
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such an SSL context. (Added by Antoine Pitrou; :issue:`8550`.)
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The :func:`ssl.wrap_socket` constructor function now takes a *ciphers*
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argument that's a string listing the encryption algorithms to be allowed; the
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format of the string is described `in the OpenSSL documentation
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<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`__. (Added
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by Antoine Pitrou; :issue:`8322`.)
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Various options have been added to the :mod:`ssl` module, such as
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:data:`~ssl.OP_NO_SSLv2` which allows to force disabling of the insecure and
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obsolete SSLv2 protocol. (Added by Antoine Pitrou; :issue:`4870`.)
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Another change makes the extension load all of OpenSSL's ciphers and digest
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algorithms so that they're all available. Some SSL certificates couldn't be
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verified, reporting an "unknown algorithm" error. (Reported by Beda Kosata,
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and fixed by Antoine Pitrou; :issue:`8484`.)
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The version of OpenSSL being used is now available as the module attributes
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:data:`ssl.OPENSSL_VERSION` (a string), :data:`ssl.OPENSSL_VERSION_INFO` (a
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5-tuple), and :data:`ssl.OPENSSL_VERSION_NUMBER` (an integer). (Added by
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Antoine Pitrou; :issue:`8321`.)
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* The previously deprecated :func:`string.maketrans` function has been removed
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in favor of the static methods, :meth:`bytes.maketrans` and
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:meth:`bytearray.maketrans`. This change solves the confusion around which
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types were supported by the :mod:`string` module. Now, :class:`str`,
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:class:`bytes`, and :class:`bytearray` each have their own **maketrans** and
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**translate** methods with intermediate translation tables of the appropriate
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type.
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(Contributed by Georg Brandl; :issue:`5675`.)
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* :class:`~poplib.POP3_SSL` class now accepts a *context* parameter, which is a
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:class:`ssl.SSLContext` object allowing bundling SSL configuration options,
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certificates and private keys into a single (potentially long-lived)
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structure.
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(Contributed by Giampaolo Rodolà; :issue:`8807`.)
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* :func:`socket.create_connection` now supports the context manager protocol
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to unconditionally consume :exc:`socket.error` exceptions and to close the
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socket when done.
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(Contributed by Giampaolo Rodolà; :issue:`9794`.)
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Multi-threading
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===============
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* The mechanism for serializing execution of concurrently running Python threads
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(generally known as the GIL or Global Interpreter Lock) has been rewritten.
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Among the objectives were more predictable switching intervals and reduced
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overhead due to lock contention and the number of ensuing system calls. The
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notion of a "check interval" to allow thread switches has been abandoned and
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replaced by an absolute duration expressed in seconds. This parameter is
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tunable through :func:`sys.setswitchinterval()`. It currently defaults to 5
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milliseconds.
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Additional details about the implementation can be read from a `python-dev
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mailing-list message
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<http://mail.python.org/pipermail/python-dev/2009-October/093321.html>`_
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(however, "priority requests" as exposed in this message have not been kept
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for inclusion).
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(Contributed by Antoine Pitrou.)
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* Recursive locks (created with the :func:`threading.RLock` API) now benefit
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from a C implementation which makes them as fast as regular locks, and between
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10x and 15x faster than their previous pure Python implementation.
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(Contributed by Antoine Pitrou; :issue:`3001`.)
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* Regular and recursive locks now accept an optional *timeout* argument to their
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:meth:`acquire` method. (Contributed by Antoine Pitrou; :issue:`7316`.)
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Similarly, :meth:`threading.Semaphore.acquire` also gains a *timeout*
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argument. (Contributed by Torsten Landschoff; :issue:`850728`.)
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Optimizations
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=============
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A number of small performance enhancements have been added:
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* JSON decoding performance is improved and memory consumption is reduced
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whenever the same string is repeated for multiple keys.
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(Contributed by Antoine Pitrou; :issue:`7451`.)
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- Python's peephole optimizer now recognizes patterns such ``x in {1, 2, 3}`` as
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being a test for membership in a set of constants. The optimizer recasts the
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:class:`set` as a :class:`frozenset` and stores the pre-built constant.
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Now that the speed penalty is gone, it is practical to start writing
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membership tests using set-notation. This style is both semantically clear
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and operationally fast::
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extension = name.rpartition('.')[2]
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if extension in {'xml', 'html', 'xhtml', 'css'}:
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handle(name)
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(Patch and additional tests by Dave Malcolm; :issue:`6690`).
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* The fast-search algorithm in stringlib is now used by the :meth:`split`,
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:meth:`rsplit`, :meth:`splitlines` and :meth:`replace` methods on
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:class:`bytes`, :class:`bytearray` and :class:`str` objects. Likewise, the
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algorithm is also used by :meth:`rfind`, :meth:`rindex`, :meth:`rsplit` and
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:meth:`rpartition`.
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(Patch by Florent Xicluna in :issue:`7622` and :issue:`7462`.)
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Filenames and Unicode
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=====================
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The filesystem encoding can be specified by setting the
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:envvar:`PYTHONFSENCODING` environment variable before running the interpreter.
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The value is an encoding name, e.g. ``iso-8859-1``. This variable is not
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available (ignored) on Windows and Mac OS X: the filesystem encoding is pinned
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to ``'mbcs'`` on Windows and ``'utf-8'`` on Mac OS X.
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The :mod:`os` module has two new functions: :func:`~os.fsencode` and
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:func:`~os.fsdecode`.
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|
|
|
.. IDLE
|
|
====
|
|
|
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* Stub
|
|
|
|
|
|
Build and C API Changes
|
|
=======================
|
|
|
|
Changes to Python's build process and to the C API include:
|
|
|
|
* 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.
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|
|
|
(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`.)
|
|
|
|
|
|
Porting to Python 3.2
|
|
=====================
|
|
|
|
This section lists previously described changes and other bugfixes that may
|
|
require changes to your code:
|
|
|
|
* :class:`bytearray` objects cannot be used anymore as filenames: convert them
|
|
to :class:`bytes`.
|
|
|
|
* PyArg_Parse*() functions:
|
|
|
|
* "t#" format has been removed: use "s#" or "s*" instead
|
|
* "w" and "w#" formats has been removed: use "w*" instead
|
|
|
|
* The :ctype:`PyCObject` type, deprecated in 3.1, has been removed. To wrap
|
|
opaque C pointers in Python objects, the :ctype:`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.
|