| **************************** |
| What's New In Python 3.1 |
| **************************** |
| |
| .. XXX Add trademark info for Apple, Microsoft. |
| |
| :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 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. (Note: I didn't get to this for 3.0. |
| GvR.) |
| |
| * 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. (Due to time |
| constraints I haven't managed to do this for 3.0. GvR.) |
| |
| * It's helpful to add the bug/patch number as a comment: |
| |
| % Patch 12345 |
| XXX Describe the transmogrify() function added to the socket |
| module. |
| (Contributed by P.Y. Developer.) |
| |
| This saves the maintainer the effort of going through the SVN log |
| when researching a change. (Again, I didn't get to this for 3.0. |
| GvR.) |
| |
| This article explains the new features in Python 3.1, compared to 3.0. |
| |
| .. 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? |
| .. sets module deprecated |
| .. ====================================================================== |
| |
| |
| PEP 372: Ordered Dictionaries |
| ============================= |
| |
| Regular Python dictionaries iterate over key/value pairs in arbitrary order. |
| Over the years, a number of authors have written alternative implementations |
| that remember the order that the keys were originally inserted. Based on |
| the experiences from those implementations, the :mod:`collections` module |
| now has an :class:`OrderedDict` class. |
| |
| The OrderedDict API is substantially the same as regular dictionaries |
| but will iterate over keys and values in a guaranteed order depending on |
| when a key was first inserted. If a new entry overwrites an existing entry, |
| the original insertion position is left unchanged. Deleting an entry and |
| reinserting it will move it to the end. |
| |
| The standard library now supports use of ordered dictionaries in several |
| modules. The :mod:`ConfigParser` module uses them by default. This lets |
| configuration files be read, modified, and then written back in their original |
| order. The :mod:`collections` module's :meth:`namedtuple._asdict` method now |
| returns an ordered dictionary with the values appearing in the same order as |
| the underlying tuple indicies. The :mod:`json` module is being built-out with |
| an *object_pairs_hook* to allow OrderedDicts to be built by the decoder. |
| Support was also added for third-party tools like `PyYAML <http://pyyaml.org/>`_. |
| |
| .. seealso:: |
| |
| :pep:`372` - Ordered Dictionaries |
| PEP written by Armin Ronacher and Raymond Hettinger. Implementation |
| written by Raymond Hettinger. |
| |
| PEP 378: Format Specifier for Thousands Separator |
| ================================================= |
| |
| The builtin :func:`format` function and the :meth:`str.format` method use |
| a mini-language that now includes a simple, non-locale aware way to format |
| a number with a thousands separator. That provides a way to humanize a |
| program's output, improving its professional appearance and readability:: |
| |
| >>> format(Decimal('1234567.89'), ',f') |
| '1,234,567.89' |
| |
| The currently supported types are :class:`int` and :class:`decimal.Decimal`. |
| Support for :class:`float` is expected before the beta release. |
| Discussions are underway about how to specify alternative separators |
| like dots, spaces, apostrophes, or underscores. Locale-aware applications |
| should use the existing *n* format specifier which already has some support |
| for thousands separators. |
| |
| .. seealso:: |
| |
| :pep:`378` - Format Specifier for Thousands Separator |
| PEP written by Raymond Hettinger; implemented by Eric Smith and |
| Mark Dickinson. |
| |
| |
| Other Language Changes |
| ====================== |
| |
| Some smaller changes made to the core Python language are: |
| |
| * The :func:`int` type 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, Victor Stinner, Raymond Hettinger, |
| and Mark Dickinson; :issue:`3439`.) |
| |
| * The fields in :func:`format` strings can now be automatically |
| numbered:: |
| |
| >>> 'Sir {} of {}'.format('Gallahad', 'Camelot') |
| 'Sir Gallahad of Camelot' |
| |
| Formerly, the string would have required numbered fields such as: |
| ``'Sir {0} of {1}'``. |
| |
| (Contributed by Eric Smith; :issue:`5237`.) |
| |
| * ``round(x, n)`` now returns an integer if *x* is an integer. |
| Previously it returned a float:: |
| |
| >>> round(1123, -2) |
| 1100 |
| |
| (Contributed by Mark Dickinson; :issue:`4707`.) |
| |
| .. ====================================================================== |
| |
| New, Improved, and Deprecated Modules |
| ===================================== |
| |
| * Added a :class:`collections.Counter` class to support convenient |
| counting of unique items in a sequence or iterable:: |
| |
| >>> Counter(['red', 'blue', 'red', 'green', 'blue', 'blue']) |
| Counter({'blue': 3, 'red': 2, 'green': 1}) |
| |
| (Contributed by Raymond Hettinger; :issue:`1696199`.) |
| |
| * Added a new module, :mod:`tkinter.ttk` for access to the Tk themed widget set. |
| The basic idea of ttk is to separate, to the extent possible, the code |
| implementing a widget's behavior from the code implementing its appearance. |
| |
| (Contributed by Kevin Walzer and Guilherme Polo; :issue:`2618` and |
| :issue:`2983`.) |
| |
| * The :class:`gzip.GzipFile` and :class:`bz2.BZ2File` classes now support |
| the context manager protocol:: |
| |
| >>> # Automatically close file after writing |
| >>> with gzip.GzipFile(filename, "wb") as f: |
| ... f.write(b"xxx") |
| |
| (Contributed by Antoine Pitrou.) |
| |
| * The :mod:`decimal.Decimal` module now supports methods for creating a |
| decimal object from a binary :class:`float`. The conversion is |
| exact but can sometimes be surprising:: |
| |
| >>> Decimal.from_float(1.1) |
| Decimal('1.100000000000000088817841970012523233890533447265625') |
| |
| The long decimal result shows the actual binary fraction being |
| stored for *1.1*. The fraction has many digits because *1.1* cannot |
| be exactly represented in binary. |
| |
| (Contributed by Raymond Hettinger and Mark Dickinson.) |
| |
| * The :mod:`itertools` module grew two new functions. The |
| :func:`itertools.combinations_with_replacement` function is one of |
| four for generating combinatorics including permutations and Cartesian |
| products. The :func:`itertools.compress` function mimics its namesake |
| from APL. Also, the existing :func:`itertools.count` function now has |
| an optional *step* argument and can accept any type of counting |
| sequence including :class:`fractions.Fraction` and |
| :class:`decimal.Decimal`:: |
| |
| >>> [p+q for p,q in combinations_with_replacement('LOVE', 2)] |
| ['LL', 'LO', 'LV', 'LE', 'OO', 'OV', 'OE', 'VV', 'VE', 'EE'] |
| |
| >>> list(compress(data=range(10), selectors=[0,0,1,1,0,1,0,1,0,0])) |
| [2, 3, 5, 7] |
| |
| >>> c = count(start=Fraction(1,2), step=Fraction(1,6)) |
| >>> next(c), next(c), next(c), next(c) |
| (Fraction(1, 2), Fraction(2, 3), Fraction(5, 6), Fraction(1, 1)) |
| |
| (Contributed by Raymond Hettinger.) |
| |
| * :func:`collections.namedtuple` now supports a keyword argument |
| *rename* which lets invalid fieldnames be automatically converted to |
| positional names in the form _0, _1, etc. This is useful when |
| the field names are being created by an external source such as a |
| CSV header, SQL field list, or user input. |
| |
| (Contributed by Raymond Hettinger; :issue:`1818`.) |
| |
| * The :func:`re.sub`, :func:`re.subn` and :func:`re.split` functions now |
| accept a flags parameter. |
| |
| (Contributed by Gregory Smith.) |
| |
| * The :mod:`runpy` module which supports the ``-m`` command line switch |
| now supports the execution of packages by looking for and executing |
| a ``__main__`` submodule when a package name is supplied. |
| |
| (Contributed by Andi Vajda; :issue:`4195`.) |
| |
| * The :mod:`pdb` module can now access and display source code loaded via |
| :mod:`zipimport` (or any other conformant :pep:`302` loader). |
| |
| (Contributed by Alexander Belopolsky; :issue:`4201`.) |
| |
| * :class:`functools.partial` objects can now be pickled. |
| |
| (Suggested by Antoine Pitrou and Jesse Noller. Implemented by |
| Jack Diedrich; :issue:`5228`.) |
| |
| * Add :mod:`pydoc` help topics for symbols so that ``help('@')`` |
| works as expected in the interactive environment. |
| |
| (Contributed by David Laban; :issue:`4739`.) |
| |
| * The :mod:`unittest` module now supports skipping individual tests or classes |
| of tests. And it supports marking a test as a expected failure, a test that |
| is known to be broken, but shouldn't be counted as a failure on a |
| TestResult:: |
| |
| class TestGizmo(unittest.TestCase): |
| |
| @unittest.skipUnless(sys.platform.startswith("win"), "requires Windows") |
| def test_gizmo_on_windows(self): |
| ... |
| |
| @unittest.expectedFailure |
| def test_gimzo_without_required_library(self): |
| ... |
| |
| (Contributed by Benjamin Peterson.) |
| |
| * A new module, :mod:`importlib` was added. It provides a complete, portable, |
| pure Python reference implementation of the *import* statement and its |
| counterpart, the :func:`__import__` function. It represents a substantial |
| step forward in documenting and defining the actions that take place during |
| imports. |
| |
| (Contributed by Brett Cannon.) |
| |
| .. ====================================================================== |
| |
| |
| Optimizations |
| ============= |
| |
| Major performance enhancements have been added: |
| |
| * The new I/O library (as defined in :pep:`3116`) was mostly written in |
| Python and quickly proved to be a problematic bottleneck in Python 3.0. |
| In Python 3.1, the I/O library has been entirely rewritten in C and is |
| 2 to 20 times faster depending on the task at hand. The pure Python |
| version is still available for experimentation purposes through |
| the ``_pyio`` module. |
| |
| (Contributed by Amaury Forgeot d'Arc and Antoine Pitrou.) |
| |
| * Added a heuristic so that tuples and dicts containing only untrackable objects |
| are not tracked by the garbage collector. This can reduce the size of |
| collections and therefore the garbage collection overhead on long-running |
| programs, depending on their particular use of datatypes. |
| |
| (Contributed by Antoine Pitrou, :issue:`4688`.) |
| |
| * Enabling a configure option named ``--with-computed-gotos`` |
| on compilers that support it (notably: gcc, SunPro, icc), the bytecode |
| evaluation loop is compiled with a new dispatch mechanism which gives |
| speedups of up to 20%, depending on the system, the compiler, and |
| the benchmark. |
| |
| (Contributed by Antoine Pitrou along with a number of other participants, |
| :issue:`4753`). |
| |
| * The decoding of UTF-8, UTF-16 and LATIN-1 is now two to four times |
| faster. |
| |
| (Contributed by Antoine Pitrou and Amaury Forgeot d'Arc, :issue:`4868`.) |
| |
| * The :mod:`json` module is getting a C extension to substantially improve |
| its performance. The code is expected to be added in-time for the beta |
| release. |
| |
| (Contributed by Bob Ippolito.) |
| |
| * 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 :attr:`sys.int_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.int_info |
| sys.int_info(bits_per_digit=30, sizeof_digit=4) |
| |
| (Contributed by Mark Dickinson; :issue:`4258`.) |
| |
| .. ====================================================================== |