[Python-checkins] python/dist/src/Doc/whatsnew whatsnew23.tex,1.132,1.133

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Update of /cvsroot/python/python/dist/src/Doc/whatsnew
In directory sc8-pr-cvs1:/tmp/cvs-serv21709

Modified Files:
	whatsnew23.tex 
Log Message:
Add PEP 307 section

Index: whatsnew23.tex
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  %======================================================================
+ \section{PEP 307: Pickle Enhancements \label{section-pep305}}
+ 
+ The \module{pickle} and \module{cPickle} modules received some
+ attention during the 2.3 development cycle.  In 2.2, new-style classes
+ could be pickled without difficult, but they weren't pickled very
+ compactly; \pep{307} quotes a trivial example where a new-style class
+ results in a pickled string three times longer than that for a classic
+ class.
+ 
+ The solution was to invent a new pickle protocol.  The
+ \function{pickle.dumps()} function has supported a text-or-binary flag 
+ for a long time.  In 2.3, this flag is redefined from a Boolean to an
+ integer; 0 is the old text-mode pickle format, 1 is the old binary
+ format, and now 2 is a new 2.3-specific format.  (A new constant,
+ \constant{pickle.HIGHEST_PROTOCOL}, can be used to select the fanciest
+ protocol available.)
+ 
+ Unpickling is no longer considered a safe operation.  2.2's
+ \module{pickle} provided hooks for trying to prevent unsafe classes
+ from being unpickled (specifically, a
+ \member{__safe_for_unpickling__} attribute), but none of this code
+ was ever audited and therefore it's all been ripped out in 2.3.  You
+ should not unpickle untrusted data in any version of Python.
+ 
+ To reduce the pickling overhead for new-style classes, a new interface
+ for customizing pickling was added using three special methods:
+ \method{__getstate__}, \method{__setstate__}, and
+ \method{__getnewargs__}.  Consult \pep{307} for the full semantics 
+ of these methods.
+ 
+ As a way to compress pickles yet further, it's now possible to use
+ integer codes instead of long strings to identify pickled classes.
+ The Python Software Foundation will maintain a list of standardized
+ codes; there's also a range of codes for private use.  Currently no
+ codes have been specified.
+ 
+ \begin{seealso}
+ 
+ \seepep{307}{Extensions to the pickle protocol}{Written and implemented 
+ by Guido van Rossum and Tim Peters.}
+ 
+ \end{seealso}
+ 
+ %======================================================================
  \section{Extended Slices\label{section-slices}}