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| -rw-r--r-- | Doc/whatsnew/2.6.rst | 145 |
1 files changed, 84 insertions, 61 deletions
diff --git a/Doc/whatsnew/2.6.rst b/Doc/whatsnew/2.6.rst index 581c1b6..759f7cb 100644 --- a/Doc/whatsnew/2.6.rst +++ b/Doc/whatsnew/2.6.rst @@ -53,6 +53,20 @@ This article explains the new features in Python 2.6. The release schedule is described in :pep:`361`; currently the final release is scheduled for October 1 2008. +The major theme of Python 2.6 is preparing the migration path to +Python 3.0, a major redesign of the language. Whenever possible, +Python 2.6 incorporates new features and syntax from 3.0 while +remaining compatible with existing code by not removing older features +or syntax. When it's not possible to do that, Python 2.6 tries to do +what it can, adding compatibility functions in a +:mod:`future_builtins` module and a :option:`-3` switch to warn about +usages that will become unsupported in 3.0. + +Some significant new packages have been added to the standard library, +such as the :mod:`multiprocessing` and :mod:`jsonlib` modules, but +there aren't many new features that aren't related to Python 3.0 in +some way. + This article doesn't attempt to provide a complete specification of the new features, but instead provides a convenient overview. For full details, you should refer to the documentation for Python 2.6. If @@ -73,9 +87,10 @@ for each change. Python 3.0 ================ -The development cycle for Python 2.6 also saw the release of the first -alphas of Python 3.0, and the development of 3.0 has influenced -a number of features in 2.6. +The development cycle for Python versions 2.6 and 3.0 was +synchronized, with the alpha and beta releases for both versions being +made on the same days. The development of 3.0 has influenced many +features in 2.6. Python 3.0 is a far-ranging redesign of Python that breaks compatibility with the 2.x series. This means that existing Python @@ -91,6 +106,14 @@ are: * The addition of :func:`functools.reduce` as a synonym for the built-in :func:`reduce` function. +Python 3.0 adds several new built-in functions and changes the +semantics of some existing built-ins. Functions that are new in 3.0 +such as :func:`bin` have simply been added to Python 2.6, but existing +built-ins haven't been changed; instead, the :mod:`future_builtins` +module has versions with the new 3.0 semantics. Code written to be +compatible with 3.0 can do ``from future_builtins import hex, map`` as +necessary. + A new command-line switch, :option:`-3`, enables warnings about features that will be removed in Python 3.0. You can run code with this switch to see how much work will be necessary to port @@ -98,35 +121,28 @@ code to 3.0. The value of this switch is available to Python code as the boolean variable :data:`sys.py3kwarning`, and to C extension code as :cdata:`Py_Py3kWarningFlag`. -Python 3.0 adds several new built-in functions and change the -semantics of some existing built-ins. Entirely new functions such as -:func:`bin` have simply been added to Python 2.6, but existing -built-ins haven't been changed; instead, the :mod:`future_builtins` -module has versions with the new 3.0 semantics. Code written to be -compatible with 3.0 can do ``from future_builtins import hex, map`` -as necessary. - .. seealso:: - The 3xxx series of PEPs, which describes the development process for - Python 3.0 and various features that have been accepted, rejected, - or are still under consideration. + The 3xxx series of PEPs, which contains proposals for Python 3.0. + :pep:`3000` describes the development process for Python 3.0. + Start with :pep:`3100` that describes the general goals for Python + 3.0, and then explore the higher-numbered PEPS that propose + specific features. -Development Changes +Changes to the Development Process ================================================== While 2.6 was being developed, the Python development process -underwent two significant changes: the developer group -switched from SourceForge's issue tracker to a customized -Roundup installation, and the documentation was converted from -LaTeX to reStructuredText. +underwent two significant changes: we switched from SourceForge's +issue tracker to a customized Roundup installation, and the +documentation was converted from LaTeX to reStructuredText. New Issue Tracker: Roundup -------------------------------------------------- -For a long time, the Python developers have been growing increasingly +For a long time, the Python developers had been growing increasingly annoyed by SourceForge's bug tracker. SourceForge's hosted solution doesn't permit much customization; for example, it wasn't possible to customize the life cycle of issues. @@ -134,14 +150,14 @@ customize the life cycle of issues. The infrastructure committee of the Python Software Foundation therefore posted a call for issue trackers, asking volunteers to set up different products and import some of the bugs and patches from -SourceForge. Four different trackers were examined: Atlassian's `Jira +SourceForge. Four different trackers were examined: `Jira <http://www.atlassian.com/software/jira/>`__, `Launchpad <http://www.launchpad.net>`__, `Roundup <http://roundup.sourceforge.net/>`__, and `Trac <http://trac.edgewall.org/>`__. The committee eventually settled on Jira and Roundup as the two candidates. Jira is a commercial product that -offers a no-cost hosted instance to free-software projects; Roundup +offers no-cost hosted instances to free-software projects; Roundup is an open-source project that requires volunteers to administer it and a server to host it. @@ -153,12 +169,13 @@ other uses in the future. Where possible, this edition of "What's New in Python" links to the bug/patch item for each change. -Hosting is kindly provided by +Hosting of the Python bug tracker is kindly provided by `Upfront Systems <http://www.upfrontsystems.co.za/>`__ of Stellenbosch, South Africa. Martin von Loewis put a lot of effort into importing existing bugs and patches from SourceForge; his scripts for this import operation are at -http://svn.python.org/view/tracker/importer/. +http://svn.python.org/view/tracker/importer/ and may be useful to +other projects wished to move from SourceForge to Roundup. .. seealso:: @@ -171,37 +188,45 @@ http://svn.python.org/view/tracker/importer/. http://roundup.sourceforge.net/ Roundup downloads and documentation. + http://svn.python.org/view/tracker/importer/ + Martin von Loewis's conversion scripts. New Documentation Format: reStructuredText Using Sphinx ----------------------------------------------------------- -Since the Python project's inception around 1989, the documentation -had been written using LaTeX. At that time, most documentation was -printed out for later study, not viewed online. LaTeX was widely used -because it provided attractive printed output while remaining -straightforward to write, once the basic rules of the markup have been +The Python documentation was written using LaTeX since the project +started around 1989. In the 1980s and early 1990s, most documentation +was printed out for later study, not viewed online. LaTeX was widely +used because it provided attractive printed output while remaining +straightforward to write once the basic rules of the markup werw learned. -LaTeX is still used today for writing technical publications destined -for printing, but the landscape for programming tools has shifted. We -no longer print out reams of documentation; instead, we browse through -it online and HTML has become the most important format to support. -Unfortunately, converting LaTeX to HTML is fairly complicated, and -Fred L. Drake Jr., the Python documentation editor for many years, -spent a lot of time wrestling the conversion process into shape. -Occasionally people would suggest converting the documentation into -SGML or, later, XML, but performing a good conversion is a major task -and no one pursued the task to completion. - -During the 2.6 development cycle, Georg Brandl put a substantial -effort into building a new toolchain for processing the documentation. -The resulting package is called Sphinx, and is available from -http://sphinx.pocoo.org/. The input format is reStructuredText, a -markup commonly used in the Python community that supports custom -extensions and directives. Sphinx concentrates on HTML output, -producing attractively styled and modern HTML, though printed output -is still supported through conversion to LaTeX. Sphinx is a -standalone package that can be used in documenting other projects. +Today LaTeX is still used for writing publications destined for +printing, but the landscape for programming tools has shifted. We no +longer print out reams of documentation; instead, we browse through it +online and HTML has become the most important format to support. +Unfortunately, converting LaTeX to HTML is fairly complicated and Fred +L. Drake Jr., the long-time Python documentation editor, spent a lot +of time maintaining the conversion process. Occasionally people would +suggest converting the documentation into SGML and later XML, but +performing a good conversion is a major task and no one ever committed +the time required to finish the job. + +During the 2.6 development cycle, Georg Brandl put a lot of effort +into building a new toolchain for processing the documentation. The +resulting package is called Sphinx, and is available from +http://sphinx.pocoo.org/. + +Sphinx concentrates on HTML output, producing attractively styled and +modern HTML; printed output is still supported through conversion to +LaTeX. The input format is reStructuredText, a markup syntax +supporting custom extensions and directives that is commonly used in +the Python community. + +Sphinx is a standalone package that can be used for writing, and +almost two dozen other projects +(`listed on the Sphinx web site <http://sphinx.pocoo.org/examples.html>`__) +have adopted Sphinx as their documentation tool. .. seealso:: @@ -219,13 +244,13 @@ PEP 343: The 'with' statement ============================= The previous version, Python 2.5, added the ':keyword:`with`' -statement an optional feature, to be enabled by a ``from __future__ +statement as an optional feature, to be enabled by a ``from __future__ import with_statement`` directive. In 2.6 the statement no longer needs to be specially enabled; this means that :keyword:`with` is now always a keyword. The rest of this section is a copy of the corresponding -section from "What's New in Python 2.5" document; if you read -it back when Python 2.5 came out, you can skip the rest of this -section. +section from the "What's New in Python 2.5" document; if you're +familiar with the ':keyword:`with`' statement +from Python 2.5, you can skip this section. The ':keyword:`with`' statement clarifies code that previously would use ``try...finally`` blocks to ensure that clean-up code is executed. In this @@ -233,7 +258,7 @@ section, I'll discuss the statement as it will commonly be used. In the next section, I'll examine the implementation details and show how to write objects for use with this statement. -The ':keyword:`with`' statement is a new control-flow structure whose basic +The ':keyword:`with`' statement is a control-flow structure whose basic structure is:: with expression [as variable]: @@ -280,7 +305,7 @@ The :mod:`threading` module's locks and condition variables also support the The lock is acquired before the block is executed and always released once the block is complete. -The new :func:`localcontext` function in the :mod:`decimal` module makes it easy +The :func:`localcontext` function in the :mod:`decimal` module makes it easy to save and restore the current decimal context, which encapsulates the desired precision and rounding characteristics for computations:: @@ -400,8 +425,8 @@ add a :keyword:`return` statement at the marked location. :: The contextlib module --------------------- -The new :mod:`contextlib` module provides some functions and a decorator that -are useful for writing objects for use with the ':keyword:`with`' statement. +The :mod:`contextlib` module provides some functions and a decorator that +are useful when writing objects for use with the ':keyword:`with`' statement. The decorator is called :func:`contextmanager`, and lets you write a single generator function instead of defining a new class. The generator should yield @@ -412,8 +437,8 @@ value that will get bound to the variable in the ':keyword:`with`' statement's executed in the :meth:`__exit__` method. Any exception raised in the block will be raised by the :keyword:`yield` statement. -Our database example from the previous section could be written using this -decorator as:: +Using this decorator, our database example from the previous section +could be written as:: from contextlib import contextmanager @@ -1025,8 +1050,6 @@ the :mod:`io` module: point Python 3.0's :mod:`io` module will be rewritten into C for speed, and perhaps the C implementation will be backported to the 2.x releases.) - .. XXX check before final release: is io.py still written in Python? - In Python 2.6, the underlying implementations haven't been restructured to build on top of the :mod:`io` module's classes. The module is being provided to make it easier to write code that's |