Against PEP 240

Tim Peters tim.one at home.com
Sat Jun 2 23:00:09 CEST 2001


[Roman Suzi]
> This said, what is the right way to deal with>currencies in Python
> right now?

[Aahz]
> Tim Peters's FixedPoint.py:
>
>
<ftp://ftp.python.org/pub/python/contrib-09-Dec-1999/DataStructures/FixedPoi
nt.py>
>
> You *probably* want to set the precision to three or four places
> so that rounding errors don't propagate.

Hmm.  It's important to note that + and - on FixedPoints never suffer
rounding errors.  Add up, say, a million dollars-and-cents FixedPoint
quantities each of precision 2, and the computed result is *exactly*
correct.  The problems with using binary f.p. in "the naive" way for
financial calcuations only start with that most dollars-and-cents inputs
can't be represented exactly; subsequent additions are also subject to
rounding errors; FixedPoint suffers neither problem.





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