[Python-Dev] Rounding Decimals (original) (raw)

Jeffrey Yasskin jyasskin at gmail.com
Mon Jan 14 01:26:34 CET 2008

On Jan 13, 2008 3:41 PM, Leif Walsh <adlaiff6 at gmail.com> wrote:

I haven't been watching the python-dev list for very long, so maybe this has already been discussed ad nauseam (in which case, sorry), but, from the devil's advocate-ish mathematics side of things, unless numbers.Decimal is planned to be implemented with infinite precision (which I doubt, but could not confirm with an admittedly small amount of research), shouldn't it implement numbers.Rational instead? Was this ever discussed, or was it just assumed that numbers.Real was the right decision?

Guido mentioned the possibility briefly at http://mail.python.org/pipermail/python-3000/2007-April/007015.html ("One could argue that float and Decimal are <:Q, but I'm not sure if that makes things better pragmatically") but never really discussed as far as I can find (although I did think about it :). I prefer having float not implement Rational (Decimal's off the table) because developers usually think of them as approximations to arbitrary, possibly-irrational, real numbers, rather than as rational numbers with some odd constraints on their denominators. That is, to me, the ABCs a type implements are more about how developers should think about the type than the implementation of the type.

[ A new thread is probably appropriate if anyone wants to discuss the philosophy, but I probably won't participate... ]

-- Namasté, Jeffrey Yasskin

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