On 07-Feb-12 03:15, Steven D'Aprano wrote:
Steve Willoughby wrote:
If you need lots of precision, you might consider using the decimal
class. It'll cost you speed vs. the native floating-point type but
won't cause you round-off errors.
I'm afraid that's not correct. Decimal is still subject to rounding errors.
>>> from decimal import Decimal
>>> x = 1/Decimal(3) # one third, as close as a Decimal can give
>>> x + x + x == 1
False
Sorry, I guess I took it for granted that was understood. I was
referring to round-off caused by binary representation of a number that
by all appearances is a simple, rational, non-repeating decimal number
expressed in base 10.
In other words, when you're adding up financial figures, you'll get an
accurate sum without "mysterious" rounding off, but of course certain
fractions which don't have a straightforward way to represent as a
decimal value, like 1/3, are going to be an issue. Good catch, though,
it was better to point that out.
--
Steve Willoughby / st...@alchemy.com
"A ship in harbor is safe, but that is not what ships are built for."
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