| **************************** |
| 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, Tarek Ziade. |
| |
| .. $Id$ |
| 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. |
| |
| Python 3.1 |
| ================ |
| |
| Much as Python 2.6 incorporated features from Python 3.0, |
| version 2.7 is influenced by features from 3.1. |
| |
| XXX mention importlib; anything else? |
| |
| One porting change: the :option:`-3` switch now automatically |
| enables the :option:`-Qwarn` switch that causes warnings |
| about using classic division with integers and long integers. |
| |
| .. ======================================================================== |
| .. Large, PEP-level features and changes should be described here. |
| .. ======================================================================== |
| |
| PEP 372: Adding an ordered dictionary to collections |
| ==================================================== |
| |
| XXX write this |
| |
| Several modules will now use :class:`OrderedDict` by default. The |
| :mod:`ConfigParser` module uses :class:`OrderedDict` for the list |
| of sections and the options within a section. |
| The :meth:`namedtuple._asdict` method returns an :class:`OrderedDict` |
| as well. |
| |
| |
| 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`.) |
| |
| * The :class:`bytearray` type's :meth:`translate` method will |
| now accept None as its first argument. (Fixed by Georg Brandl; |
| :issue:`4759`.) |
| |
| .. ====================================================================== |
| |
| |
| Optimizations |
| ------------- |
| |
| Several performance enhancements have been added: |
| |
| .. * A new :program:`configure` option, :option:`--with-computed-gotos`, |
| compiles the main bytecode interpreter loop using a new dispatch |
| mechanism that gives speedups of up to 20%, depending on the system |
| and benchmark. The new mechanism is only supported on certain |
| compilers, such as gcc, SunPro, and icc. |
| |
| * 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. In Python 2.7, this is now true for |
| tuples and dicts containing atomic types (such as ints, strings, |
| etc.). Transitively, a dict containing tuples of atomic types won't |
| be tracked either. This helps reduce the cost of each |
| garbage collection by decreasing the number of objects to be |
| considered and traversed by the collector. |
| (Contributed by Antoine Pitrou; :issue:`4688`.) |
| |
| * 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 |
| :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`.) |
| |
| Another set of changes made long objects a few bytes smaller: 2 bytes |
| smaller on 32-bit systems and 6 bytes on 64-bit. |
| (Contributed by Mark Dickinson; :issue:`5260`.) |
| |
| * The division algorithm for long integers has been made faster |
| by tightening the inner loop, doing shifts instead of multiplications, |
| and fixing an unnecessary extra iteration. |
| Various benchmarks show speedups of between 50% and 150% for long |
| integer divisions and modulo operations. |
| (Contributed by Mark Dickinson; :issue:`5512`.) |
| |
| * The implementation of ``%`` checks for the left-side operand being |
| a Python string and special-cases it; this results in a 1-3% |
| performance increase for applications that frequently use ``%`` |
| with strings, such as templating libraries. |
| (Implemented by Collin Winter; :issue:`5176`.) |
| |
| * List comprehensions with an ``if`` condition are compiled into |
| faster bytecode. (Patch by Antoine Pitrou, back-ported to 2.7 |
| by Jeffrey Yasskin; :issue:`4715`.) |
| |
| .. ====================================================================== |
| |
| 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. |
| |
| * 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 :class:`namedtuple` class now has an optional *rename* parameter. |
| If *rename* is True, field names that are invalid because they've |
| been repeated or that aren't legal Python identifiers will be |
| renamed to legal names that are derived from the field's |
| position within the list of fields: |
| |
| >>> T=namedtuple('T', ['field1', '$illegal', 'for', 'field2'], rename=True) |
| >>> T._fields |
| ('field1', '_1', '_2', 'field2') |
| |
| (Added by Raymond Hettinger; :issue:`1818`.) |
| |
| * In Distutils, :func:`distutils.sdist.add_defaults` now uses |
| *package_dir* and *data_files* to create the MANIFEST file. |
| |
| It is no longer mandatory 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 Ziade, |
| based on an initial contribution by Nathan Van Gheem; :issue:`4394`.) |
| |
| * New method: the :class:`Decimal` class gained a |
| :meth:`from_float` class method that performs an exact conversion |
| of a floating-point number to a :class:`Decimal`. |
| Note that this is an **exact** conversion that strives for the |
| closest decimal approximation to the floating-point representation's value; |
| the resulting decimal value will therefore still include the inaccuracy, |
| if any. |
| For example, ``Decimal.from_float(0.1)`` returns |
| ``Decimal('0.1000000000000000055511151231257827021181583404541015625')``. |
| (Implemented by Raymond Hettinger; :issue:`4796`.) |
| |
| * 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`.) |
| |
| * 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`.) |
| It's now possible to override the modification time |
| recorded in a gzipped file by providing an optional timestamp to |
| the constructor. (Contributed by Jacques Frechet; :issue:`4272`.) |
| |
| * The :class:`io.FileIO` class now raises an :exc:`OSError` when passed |
| an invalid file descriptor. (Implemented by Benjamin Peterson; |
| :issue:`4991`.) |
| |
| * New function: ``itertools.compress(*data*, *selectors*)`` takes two |
| iterators. Elements of *data* are returned if the corresponding |
| value in *selectors* is True:: |
| |
| itertools.compress('ABCDEF', [1,0,1,0,1,1]) => |
| A, C, E, F |
| |
| New function: ``itertools.combinations_with_replacement(*iter*, *r*)`` |
| returns all the possible *r*-length combinations of elements from the |
| iterable *iter*. Unlike :func:`combinations`, individual elements |
| can be repeated in the generated combinations:: |
| |
| itertools.combinations_with_replacement('abc', 2) => |
| ('a', 'a'), ('a', 'b'), ('a', 'c'), |
| ('b', 'b'), ('b', 'c'), ('c', 'c') |
| |
| Note that elements are treated as unique depending on their position |
| in the input, not their actual values. |
| |
| The :class:`itertools.count` function now has a *step* argument that |
| allows incrementing by values other than 1. :func:`count` also |
| now allows keyword arguments, and using non-integer values such as |
| floats or :class:`Decimal` instances. (Implemented by Raymond |
| Hettinger; :issue:`5032`.) |
| |
| :func:`itertools.combinations` and :func:`itertools.product` were |
| previously raising :exc:`ValueError` for values of *r* larger than |
| the input iterable. This was deemed a specification error, so they |
| now return an empty iterator. (Fixed by Raymond Hettinger; :issue:`4816`.) |
| |
| * The :mod:`json` module was upgraded to version 2.0.9 of the |
| simplejson package, which includes a C extension that makes |
| encoding and decoding faster. |
| (Contributed by Bob Ippolito; :issue:`4136`.) |
| |
| To support the new :class:`OrderedDict` type, :func:`json.load` |
| now has an optional *object_pairs_hook* parameter that will be called |
| with any object literal that decodes to a list of pairs. |
| (Contributed by Raymond Hettinger; :issue:`5381`.) |
| |
| * 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 when 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 ``sys.version_info`` value is now a named tuple, with attributes |
| named ``major``, ``minor``, ``micro``, ``releaselevel``, and ``serial``. |
| (Contributed by Ross Light; :issue:`4285`.) |
| |
| * The :mod:`unittest` module was enhanced in several ways. |
| Test cases can raise the :exc:`SkipTest` exception to skip a test. |
| (:issue:`1034053`.) |
| It will now use 'x' for expected failures |
| and 'u' for unexpected successes when run in its verbose mode. |
| (Contributed by Benjamin Peterson.) |
| |
| The :meth:`assertRaises` and :meth:`failUnlessRaises` methods now |
| return a context handler when called without providing a callable |
| object to run. For example, you can write this:: |
| |
| with self.assertRaises(KeyError): |
| raise ValueError |
| |
| (Implemented by Antoine Pitrou; :issue:`4444`.) |
| |
| * 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`.) |
| |
| :mod:`zipfile` now supports archiving empty directories and |
| extracts them correctly. (Fixed by Kuba Wieczorek; :issue:`4710`.) |
| |
| .. ====================================================================== |
| .. whole new modules get described in subsections here |
| |
| importlib: Importing Modules |
| ------------------------------ |
| |
| XXX write this |
| |
| 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`.) |
| |
| * The :program:`configure` script now checks for floating-point rounding bugs |
| on certain 32-bit Intel chips and defines a :cmacro:`X87_DOUBLE_ROUNDING` |
| preprocessor definition. No code currently uses this definition, |
| but it's available if anyone wishes to use it. |
| (Added by Mark Dickinson; :issue:`2937`.) |
| |
| .. ====================================================================== |
| |
| 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 |
| ----------------------------------- |
| |
| * The ``/Library/Python/2.7/site-packages`` is now appended to |
| ``sys.path``, in order to share added packages between the system |
| installation and a user-installed copy of the same version. |
| (Changed by Ronald Oussoren; :issue:`4865`.) |
| |
| |
| Other Changes and Fixes |
| ======================= |
| |
| * When importing a module from a :file:`.pyc` or :file:`.pyo` file |
| with an existing :file:`.py` counterpart, the :attr:`co_filename` |
| attributes of all code objects if the original filename is obsolete, |
| which can happen if the file has been renamed, moved, or is accessed |
| through different paths. (Patch by Ziga Seilnacht and Jean-Paul |
| Calderone; :issue:`1180193`.) |
| |
| * The :file:`regrtest.py` script now takes a :option:`--randseed=` |
| switch that takes an integer that will be used as the random seed |
| for the :option:`-r` option that executes tests in random order. |
| The :option:`-r` option also now reports the seed that was used |
| (Added by Collin Winter.) |
| |
| |
| .. ====================================================================== |
| |
| 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. |
| |