[Python-checkins] python/dist/src/Doc/whatsnew whatsnew24.tex, 1.55, 1.56

[rhettinger at users.sourceforge.net]

Update of /cvsroot/python/python/dist/src/Doc/whatsnew
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv5372

Modified Files:
	whatsnew24.tex 
Log Message:
Move Decimal from the sandbox into production.



Index: whatsnew24.tex
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RCS file: /cvsroot/python/python/dist/src/Doc/whatsnew/whatsnew24.tex,v
retrieving revision 1.55
retrieving revision 1.56
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--- whatsnew24.tex	1 Jul 2004 11:52:15 -0000	1.56
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  %======================================================================
+ \section{PEP 327: Decimal Data Type}
+ 
+ A new module, \module{decimal}, offers a \class{Decimal} data type for
+ decimal floating point arithmetic.  Compared to the built-in \class{float}
+ type implemented with binary floating point, the new class is especially
+ useful for financial applications and other uses which require exact
+ decimal representation, control over precision, control over rounding
+ to meet legal or regulatory requirements, tracking of significant
+ decimal places, or for applications where the user expects the results
+ to match hand calculations done the way they were taught in school.
+ 
+ For example, calculating a 5% tax on a 70 cent phone charge gives
+ different results in decimal floating point and binary floating point
+ with the difference being significant when rounding to the nearest
+ cent:
+ 
+ \begin{verbatim}
+ >>> from decimal import *       
+ >>> Decimal('0.70') * Decimal('1.05')
+ Decimal("0.7350")
+ >>> .70 * 1.05
+ 0.73499999999999999       
+ \end{verbatim}
+ 
+ Note that the \class{Decimal} result keeps a trailing zero, automatically
+ inferring four place significance from two digit mulitiplicands.  A key
+ goal is to reproduce the mathematics we do by hand and avoid the tricky
+ issues that arise when decimal numbers cannot be represented exactly in
+ binary floating point.
+ 
+ Exact representation enables the \class{Decimal} class to perform
+ modulo calculations and equality tests that would fail in binary
+ floating point:
+ 
+ \begin{verbatim}
+ >>> Decimal('1.00') % Decimal('.10')
+ Decimal("0.00")
+ >>> 1.00 % 0.10
+ 0.09999999999999995
+        
+ >>> sum([Decimal('0.1')]*10) == Decimal('1.0')
+ True
+ >>> sum([0.1]*10) == 1.0
+ False      
+ \end{verbatim}
+ 
+ The \module{decimal} module also allows arbitrarily large precisions to be
+ set for calculation:
+ 
+ \begin{verbatim}
+ >>> getcontext().prec = 24
+ >>> Decimal(1) / Decimal(7)
+ Decimal("0.142857142857142857142857")
+ \end{verbatim}
+        
+ \begin{seealso}
+ \seepep{327}{Decimal Data Type}{Written by Facundo Batista and implemented
+   by Eric Price, Facundo Bastista, Raymond Hettinger, Aahz, and Tim Peters.}
+ \end{seealso}      
+ 
+ 
+ %======================================================================
  \section{Other Language Changes}