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| -rw-r--r-- | Doc/whatsnew/3.1.rst | 84 |
1 files changed, 82 insertions, 2 deletions
diff --git a/Doc/whatsnew/3.1.rst b/Doc/whatsnew/3.1.rst index 40d7afd..2d3b20b 100644 --- a/Doc/whatsnew/3.1.rst +++ b/Doc/whatsnew/3.1.rst @@ -4,7 +4,7 @@ .. XXX Add trademark info for Apple, Microsoft. -:Author: No one so far +:Author: Raymond Hettinger :Release: |release| :Date: |today| @@ -66,6 +66,59 @@ This article explains the new features in Python 3.1, compared to 3.0. .. ====================================================================== +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` modules 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 a dictionary with the values appearing in the same order as the +underlying tuple.count 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 builtin for third-party tools like PyYAML. + +.. seealso:: + + :pep:`372` - Ordered Dictionaries + PEP written by Armin Roancher and Raymond D. Hettinger; implemented 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`. +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. + +.. seealso:: + + :pep:`378` - Format Specifier for Thousands Separator + PEP written by Raymond Hettinger; implemented by Eric Smith and + Mark Dickinson. + + Other Language Changes ====================== @@ -107,10 +160,36 @@ Some smaller changes made to the core Python language are: >>> sys.int_info sys.int_info(bits_per_digit=30, sizeof_digit=4) - (Contributed by Mark Dickinson; :issue:`4258`.) +* 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`.) + +* The :class:`gzip.GzipFile` and :class:`bz2.BZ2File` classs now support + the context manager protocol. + + (Contributed by Jacques Frechet; :issue:`4272`.) + +* The :mod:`Decimal` module now supports two new methods to create a + decimal object that 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.) + + .. ====================================================================== @@ -134,5 +213,6 @@ Major performance enhancements have been added: (Contributed by Antoine Pitrou, :issue:`4753`.) +XXX The JSON module is getting a C extension for speed. .. ====================================================================== |