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Write two sections, and write some partial text for some other sections
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Andrew M. Kuchling
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\documentclass{howto}
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% $Id$
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\title{What's New in Python 2.3}
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@ -14,7 +13,7 @@
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%\section{Introduction \label{intro}}
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{\large This article is a draft, and is currently up to date for some
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random version of the CVS tree around March 26 2002. Please send any
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random version of the CVS tree around May 26 2002. Please send any
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additions, comments or errata to the author.}
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This article explains the new features in Python 2.3. The tentative
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@ -34,6 +33,7 @@ a particular new feature.
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%======================================================================
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\section{PEP 255: Simple Generators}
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\label{section-generators}
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In Python 2.2, generators were added as an optional feature, to be
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enabled by a \code{from __future__ import generators} directive. In
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@ -184,12 +184,30 @@ and Tim Peters, with other fixes from the Python Labs crew.}
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%======================================================================
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\section{PEP 278: Universal Newline Support}
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XXX write this section
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The three major operating systems used today are Microsoft Windows,
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Apple's Macintosh OS, and the various Unix derivatives. A minor
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irritation is that these three platforms all use different characters
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to mark the ends of lines in text files. Unix uses character 10, the
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ASCII linefeed, MacOS uses character 13, the ASCII carriage return,
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and Windows uses a two-character sequence of carriage return plus a
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newline.
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%Highlights: import and friends will understand any of \r, \n and \r\n
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%as end of line. Python file input will do the same if you use mode 'U'.
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%Everything can be disabled by configuring with --without-universal-newlines.
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Python's file objects can now support end of line conventions other
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than the one followed by the platform on which Python is running.
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Opening a file with the mode \samp{U} or \samp{rU} will open a file
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for reading in universal newline mode. All three line ending
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conventions will be translated to a \samp{\e n} in the strings
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returned by the various file methods such as \method{read()} and
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\method{readline()}.
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Universal newline support is also used when importing modules and when
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executing a file with the \function{execfile()} function. This means
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that Python modules can be shared between all three operating systems
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without needing to convert the line-endings.
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This feature can be disabled at compile-time by specifying the
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\longprogramopt{without-universal-newlines} when running Python's
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configure script.
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\begin{seealso}
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@ -200,8 +218,72 @@ and implemented by Jack Jansen.}
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%======================================================================
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\section{PEP 285: The \class{bool} Type}
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\label{section-bool}
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XXX write this section
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A Boolean type was added to Python 2.3. Two new constants were added
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to the \module{__builtin__} module, \constant{True} and
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\constant{False}. The type object for this new type is named
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\class{bool}; the constructor for it takes any Python value and
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converts it to \constant{True} or \constant{False}.
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\begin{verbatim}
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>>> bool(1)
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True
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>>> bool(0)
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False
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>>> bool([])
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False
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>>> bool( (1,) )
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True
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\end{verbatim}
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Most of the standard library modules and built-in functions have been
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changed to return Booleans.
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\begin{verbatim}
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>>> o = []
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>>> hasattr(o, 'append')
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True
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>>> isinstance(o, list)
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True
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>>> isinstance(o, tuple)
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False
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\end{verbatim}
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Python's Booleans were added with the primary goal of making code
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clearer. For example, if you're reading a function and encounter the
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statement \code{return 1}, you might wonder whether the \samp{1}
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represents a truth value, or whether it's an index, or whether it's a
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coefficient that multiplies some other quantity. If the statement is
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\code{return True}, however, the meaning of the return value is quite
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clearly a truth value.
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Python's Booleans were not added for the sake of strict type-checking.
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A very strict language such as Pascal
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% XXX is Pascal the right example here?
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would also prevent you performing arithmetic with Booleans, and would
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require that the expression in an \keyword{if} statement always
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evaluate to a Boolean. Python is not this strict, and it never will
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be. (\pep{285} explicitly says this.) So you can still use any
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expression in an \keyword{if}, even ones that evaluate to a list or
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tuple or some random object, and the Boolean type is a subclass of the
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\class{int} class, so arithmetic using a Boolean still works.
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\begin{verbatim}
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>>> True + 1
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2
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>>> False + 1
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1
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>>> False * 75
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0
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>>> True * 75
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75
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\end{verbatim}
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To sum up \constant{True} and \constant{False} in a sentence: they're
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alternative ways to spell the integer values 1 and 0, with the single
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difference that \function{str()} and \function{repr()} return the
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strings \samp{True} and \samp{False} instead of \samp{1} and \samp{0}.
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\begin{seealso}
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@ -213,60 +295,158 @@ XXX write this section
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%======================================================================
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\section{New and Improved Modules}
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arraymodule.c: - add Py_UNICODE arrays
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- support +=, *=
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As usual, Python's standard modules had a number of enhancements and
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bug fixes. Here's a partial list; consult the \file{Misc/NEWS} file
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in the source tree, or the CVS logs, for a more complete list.
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\begin{itemize}
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\item One minor but far-reaching change is that the names of extension
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types defined by the modules included with Python now contain the
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module and a \samp{.} in front of the type name. For example, in
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Python 2.2, if you created a socket and printed its
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\member{__class__}, you'd get this output:
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\begin{verbatim}
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>>> s = socket.socket()
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>>> s.__class__
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<type 'socket'>
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\end{verbatim}
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In 2.3, you get this:
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\begin{verbatim}
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>>> s.__class__
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<type '_socket.socket'>
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\end{verbatim}
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\item The \method{strip()}, \method{lstrip()}, and \method{rstrip()}
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string methods now have an optional argument for specifying the
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characters to strip. The default is still to remove all whitespace
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characters:
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\begin{verbatim}
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>>> ' abc '.strip()
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'abc'
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>>> '><><abc<><><>'.strip('<>')
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'abc'
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>>> '><><abc<><><>\n'.strip('<>')
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'abc<><><>\n'
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>>> u'\u4000\u4001abc\u4000'.strip(u'\u4000')
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u'\u4001abc'
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>>>
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\end{verbatim}
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\item Another new string method is \method{zfill()}, originally a
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function in the \module{string} module. \method{zfill()} pads a
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numeric string with zeros on the left until it's the specified width.
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Note that the \code{\%} operator is still more flexible and powerful
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than \method{zfill()}.
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\begin{verbatim}
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>>> '45'.zfill(4)
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'0045'
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>>> '12345'.zfill(4)
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'12345'
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>>> 'goofy'.zfill(4)
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'0goofy'
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\end{verbatim}
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\item Dictionaries have a new method, method{pop(\var{key})}, that
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returns the value corresponding to \var{key} and removes that
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key/value pair from the dictionary. \method{pop()} will raise a
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\exception{KeyError} if the requsted key isn't present in the
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dictionary:
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\begin{verbatim}
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>>> d = {1:2}
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>>> d
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{1: 2}
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>>> d.pop(4)
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Traceback (most recent call last):
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File ``<stdin>'', line 1, in ?
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KeyError: 4
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>>> d.pop(1)
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2
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>>> d.pop(1)
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Traceback (most recent call last):
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File ``<stdin>'', line 1, in ?
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KeyError: pop(): dictionary is empty
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>>> d
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{}
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>>>
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\end{verbatim}
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distutils: command/bdist_packager, support for Solaris pkgtool
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and HP-UX swinstall
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Return enhanced tuples in grpmodule
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posixmodule: killpg, mknod, fchdir,
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\item Two new functions, \function{killpg()} and \function{mknod()},
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were added to the \module{posix} module that underlies the \module{os}
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module.
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Expat is now included with the Python source
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\item (XXX write this) arraymodule.c: - add Py_UNICODE arrays
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- support +=, *=
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Readline: Add get_history_item, get_current_history_length, and
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redisplay functions.
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\item The \module{grp} module now returns enhanced tuples:
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Add optional arg to string methods strip(), lstrip(), rstrip().
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The optional arg specifies characters to delete.
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\begin{verbatim}
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>>> import grp
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>>> g = grp.getgrnam('amk')
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>>> g.gr_name, g.gr_gid
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('amk', 500)
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\end{verbatim}
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New method: string.zfill()
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\item The \module{readline} module also gained a number of new
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functions: \function{get_history_item()},
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\function{get_current_history_length()}, and \function{redisplay()}.
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\end{itemize}
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Add dict method pop().
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New enumerate() built-in.
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%======================================================================
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\section{Interpreter Changes and Fixes}
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file object can now be subtyped (did this not work before?)
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Here are the changes that Python 2.3 makes to the core language.
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yield is now always available
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\begin{itemize}
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\item The \keyword{yield} statement is now always a keyword, as
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described in section~\ref{section-generators}.
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This adds the module name and a dot in front of the type name in every
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type object initializer, except for built-in types (and those that
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already had this). Note that it touches lots of Mac modules -- I have
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no way to test these but the changes look right. Apologies if they're
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not. This also touches the weakref docs, which contains a sample type
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object initializer. It also touches the mmap test output, because the
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mmap type's repr is included in that output. It touches object.h to
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put the correct description in a comment.
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\item Two new constants, \constant{True} and \constant{False} were
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added along with the built-in \class{bool} type, as described in
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section~\ref{section-bool}.
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\item The \class{file} type can now be subtyped. (XXX did this not work
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before? Thought I used it in an example in the 2.2 What's New document...)
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\item File objects also manage their internal string buffer
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differently by increasing it exponentially when needed.
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This results in the benchmark tests in \file{Lib/test/test_bufio.py}
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speeding up from 57 seconds to 1.7 seconds, according to one
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measurement.
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\end{itemize}
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File objects: Grow the string buffer at a mildly exponential rate for
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the getc version of get_line. This makes test_bufio finish in 1.7
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seconds instead of 57 seconds on my machine (with Py_DEBUG defined).
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%======================================================================
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\section{Other Changes and Fixes}
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XXX write this
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The tools used to build the documentation now work under Cygwin as
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well as \UNIX.
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% ======================================================================
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\section{C Interface Changes}
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Patch \#527027: Allow building python as shared library with
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% ======================================================================
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\section{Build and C API Changes}
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XXX write this
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\begin{itemize}
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\item Patch \#527027: Allow building python as shared library with
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--enable-shared
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pymalloc is now enabled by default (also mention debug-mode pymalloc)
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@ -277,6 +457,10 @@ PyObject_DelItemString() added
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PyArg_NoArgs macro is now deprecated
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\item The source code for the Expat XML parser is now included with
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the Python source, so the \module{pyexpat} module is no longer
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dependent on having a system library containing Expat.
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===
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Introduce two new flag bits that can be set in a PyMethodDef method
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descriptor, as used for the tp_methods slot of a type. These new flag
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@ -297,7 +481,11 @@ these special method types are not meaningful in that case; a
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ValueError will be raised if these flags are found in that context.
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===
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Ports:
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\end{itemize}
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\subsection{Port-Specific Changes}
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XXX write this
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OS/2 EMX port
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@ -319,6 +507,3 @@ suggestions, corrections and assistance with various drafts of this
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article: Fred~L. Drake, Jr.
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\end{document}
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