[Python-Dev] Decimal <-> float comparisons in py3k. (original) (raw)
Mark Dickinson dickinsm at gmail.com
Wed Mar 17 14:39:14 CET 2010
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On Tue, Mar 16, 2010 at 10:16 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
Mark Dickinson wrote:
On Tue, Mar 16, 2010 at 3:58 PM, P.J. Eby <pje at telecommunity.com> wrote:
If not, it might be confusing if a number that prints as '.1' compares unequal to Decimal('.1'). Agreed, but this is just your everyday floating-point confusion, to be dealt with by social means (e.g., educating the programmer). Seems to me that this education would mostly consist of saying "don't compare floats and decimals", which is why I think that disallowing them in the first place would be better.
I was thinking of something more along the lines of: "Sure, go ahead and compare floats and decimals, but be aware that float('1.1') is not exactly 1.1, so don't complain when 1.1 == Decimal('1.1') returns False." For me, this actually a plus of allowing these comparisons: it makes the education easier. "Look, the binary float stored for 1.1 is actually larger than 1.1, and here's the proof: >>> 1.1 > Decimal('1.1') -> True."
-- Mark
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