Against PEP 240

Aahz Maruch aahz at panix.com
Sun Jun 3 03:56:47 CEST 2001


In article <mailman.991515668.4621.python-list at python.org>,
Tim Peters <tim.one at home.com> wrote:
>[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.

Right.  I was assuming because of the plural that Roman was likely to
want to do currency conversions, which involves multiplication at the
very least.
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