**************************** What's New in Python 2.7 **************************** :Author: A.M. Kuchling (amk at amk.ca) :Release: |release| :Date: |today| .. Fix accents on Kristjan Valur Jonsson, Fuerstenau. .. $Id$ 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 to some degree. * 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 bug/patch number in a parenthetical comment. XXX Describe the transmogrify() function added to the socket module. (Contributed by P.Y. Developer; :issue:`12345`.) This saves the maintainer some effort going through the SVN logs when researching a change. This article explains the new features in Python 2.7. No release schedule has been decided yet for 2.7. .. Compare with previous release in 2 - 3 sentences here. add hyperlink when the documentation becomes available online. .. ======================================================================== .. Large, PEP-level features and changes should be described here. .. Should there be a new section here for 3k migration? .. Or perhaps a more general section describing module changes/deprecation? .. ======================================================================== Other Language Changes ====================== Some smaller changes made to the core Python language are: * The :func:`int` and :func:`long` types gained a ``bit_length`` method that returns the number of bits necessary to represent its argument in binary:: >>> n = 37 >>> bin(37) '0b100101' >>> n.bit_length() 6 >>> n = 2**123-1 >>> n.bit_length() 123 >>> (n+1).bit_length() 124 (Contributed by Fredrik Johansson and Victor Stinner; :issue:`3439`.) * Integers are now stored internally either in base 2**15 or in base 2**30, the base being determined at build time. Previously, they were always stored in base 2**15. Using base 2**30 gives significant performance improvements on 64-bit machines, but benchmark results on 32-bit machines have been mixed. Therefore, the default is to use base 2**30 on 64-bit machines and base 2**15 on 32-bit machines; on Unix, there's a new configure option --enable-big-digits that can be used to override this default. Apart from the performance improvements this change should be invisible to end users, with one exception: for testing and debugging purposes there's a new structseq ``sys.long_info`` that provides information about the internal format, giving the number of bits per digit and the size in bytes of the C type used to store each digit:: >>> import sys >>> sys.long_info sys.long_info(bits_per_digit=30, sizeof_digit=4) (Contributed by Mark Dickinson; :issue:`4258`.) .. ====================================================================== Optimizations ------------- A few performance enhancements have been added: * The garbage collector now performs better when many objects are being allocated without deallocating any. A full garbage collection pass is only performed when the middle generation has been collected 10 times and when the number of survivor objects from the middle generation exceeds 10% of the number of objects in the oldest generation. The second condition was added to reduce the number of full garbage collections as the number of objects on the heap grows, avoiding quadratic performance when allocating very many objects. (Suggested by Martin von Loewis and implemented by Antoine Pitrou; :issue:`4074`.) * The garbage collector tries to avoid tracking simple containers which can't be part of a cycle. As of now, this is true for tuples and dicts containing atomic types (such as ints, strings, etc.). Transitively, a dict containing tuples of atomic types won't be tracked either. This helps bring down the individual cost of each garbage collection, since it decreases the number of objects to be considered and traversed by the collector. To help diagnosing this optimization, a new function in the :mod:`gc` module, :func:`is_tracked`, returns True if a given instance is tracked by the garbage collector, False otherwise. (Contributed by Antoine Pitrou; :issue:`4688`.) .. ====================================================================== New, Improved, and Deprecated Modules ===================================== As in every release, Python's standard library received a number of enhancements and bug fixes. Here's a partial list of the most notable changes, sorted alphabetically by module name. Consult the :file:`Misc/NEWS` file in the source tree for a more complete list of changes, or look through the Subversion logs for all the details. * In Distutils, distutils.sdist.add_defaults now uses package_dir and data_files to feed MANIFEST. * It is not mandatory anymore to store clear text passwords in the :file:`.pypirc` file when registering and uploading packages to PyPI. As long as the username is present in that file, the :mod:`distutils` package will prompt for the password if not present. (Added by tarek, with the initial contribution of Nathan Van Gheem; :issue:`4394`.) * The :mod:`bz2` module's :class:`BZ2File` now supports the context management protocol, so you can write ``with bz2.BZ2File(...) as f: ...``. (Contributed by Hagen Fuerstenau; :issue:`3860`.) * A new :class:`Counter` class in the :mod:`collections` module is useful for tallying data. :class:`Counter` instances behave mostly like dictionaries but return zero for missing keys instead of raising a :exc:`KeyError`:: >>> from collections import Counter >>> c=Counter() >>> for letter in 'here is a sample of english text': ... c[letter] += 1 ... >>> c Counter({' ': 6, 'e': 5, 's': 3, 'a': 2, 'i': 2, 'h': 2, 'l': 2, 't': 2, 'g': 1, 'f': 1, 'm': 1, 'o': 1, 'n': 1, 'p': 1, 'r': 1, 'x': 1}) >>> c['e'] 5 >>> c['z'] 0 There are two additional :class:`Counter` methods: :meth:`most_common` returns the N most common elements and their counts, and :meth:`elements` returns an iterator over the contained element, repeating each element as many times as its count:: >>> c.most_common(5) [(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)] >>> c.elements() -> 'a', 'a', ' ', ' ', ' ', ' ', ' ', ' ', 'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i', 'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's', 's', 's', 'r', 't', 't', 'x'] Contributed by Raymond Hettinger; :issue:`1696199`. * The :mod:`gzip` module's :class:`GzipFile` now supports the context management protocol, so you can write ``with gzip.GzipFile(...) as f: ...``. (Contributed by Hagen Fuerstenau; :issue:`3860`.) * The :class:`io.FileIO` class now raises an :exc:`OSError` when passed an invalid file descriptor. (Implemented by Benjamin Peterson; :issue:`4991`.) * The :mod:`pydoc` module now has help for the various symbols that Python uses. You can now do ``help('<<')`` or ``help('@')``, for example. (Contributed by David Laban; :issue:`4739`.) * A new function in the :mod:`subprocess` module, :func:`check_output`, runs a command with a specified set of arguments and returns the command's output as a string if the command runs without error, or raises a :exc:`CalledProcessError` exception otherwise. :: >>> subprocess.check_output(['df', '-h', '.']) 'Filesystem Size Used Avail Capacity Mounted on\n /dev/disk0s2 52G 49G 3.0G 94% /\n' >>> subprocess.check_output(['df', '-h', '/bogus']) ... subprocess.CalledProcessError: Command '['df', '-h', '/bogus']' returned non-zero exit status 1 (Contributed by Gregory P. Smith.) * The :func:`is_zipfile` function in the :mod:`zipfile` module will now accept a file object, in addition to the path names accepted in earlier versions. (Contributed by Gabriel Genellina; :issue:`4756`.) .. ====================================================================== .. whole new modules get described in subsections here ttk: Themed Widgets for Tk -------------------------- Tcl/Tk 8.5 includes a set of themed widgets that re-implement basic Tk widgets but have a more customizable appearance and can therefore more closely resemble the native platform's widgets. This widget set was originally called Tile, but was renamed to Ttk (for "themed Tk") on being added to Tcl/Tck release 8.5. XXX write a brief discussion and an example here. The :mod:`ttk` module was written by Guilherme Polo and added in :issue:`2983`. An alternate version called ``Tile.py``, written by Martin Franklin and maintained by Kevin Walzer, was proposed for inclusion in :issue:`2618`, but the authors argued that Guilherme Polo's work was more comprehensive. .. ====================================================================== Build and C API Changes ======================= Changes to Python's build process and to the C API include: * If you use the :file:`.gdbinit` file provided with Python, the "pyo" macro in the 2.7 version will now work when the thread being debugged doesn't hold the GIL; the macro will now acquire it before printing. (Contributed by Victor Stinner; :issue:`3632`.) * :cfunc:`Py_AddPendingCall` is now thread safe, letting any worker thread submit notifications to the main Python thread. This is particularly useful for asynchronous IO operations. (Contributed by Kristjan Valur Jonsson; :issue:`4293`.) .. ====================================================================== Port-Specific Changes: Windows ----------------------------------- * The :mod:`msvcrt` module now contains some constants from the :file:`crtassem.h` header file: :data:`CRT_ASSEMBLY_VERSION`, :data:`VC_ASSEMBLY_PUBLICKEYTOKEN`, and :data:`LIBRARIES_ASSEMBLY_NAME_PREFIX`. (Contributed by David Cournapeau; :issue:`4365`.) * The new :cfunc:`_beginthreadex` API is used to start threads, and the native thread-local storage functions are now used. (Contributed by Kristjan Valur Jonsson; :issue:`3582`.) .. ====================================================================== Port-Specific Changes: Mac OS X ----------------------------------- .. ====================================================================== Porting to Python 2.7 ===================== This section lists previously described changes and other bugfixes that may require changes to your code: To be written. .. ====================================================================== .. _acks27: Acknowledgements ================ The author would like to thank the following people for offering suggestions, corrections and assistance with various drafts of this article: no one yet.