[Tutor] range function and floats?

[Wayne Werner]

On Wed, Jan 5, 2011 at 4:59 PM, Steven D'Aprano <steve at pearwood.info> wrote:

> Wayne Werner wrote:
>
>> <snip>
>
> I never said rounding errors - I said "pesky floating point errors". When
>>
>
> Which ARE rounding errors. They're *all* rounding errors, caused by the
> same fundamental issue --  the impossibility of representing some specific
> exact number in the finite number of bits, or digits, available.
>
> Only the specific numbers change, not the existence of the errors.


So truncation == rounding. I can agree with that, though they've always
seemed distinct entities before, because you can round up or round down, but
truncation simply removes what you don't want, which is equivalent to
rounding down at whatever precision you want.

Round down the tens place (or truncate anything lower than 1e2): 10000010
=> 10000000
Round down the thousandth place (or truncate everything "past" 1e-2): 1/3 =
.3333(repeating) => .330

Having re-read and thought about it for a while, I think my argument simply
distills down to this: using Decimal both allows you control over your
significant figures, and (at least for me) *requires* you to think about
what sort of truncation/rounding you will experience, and let's be honest -
usually the source of errors is we, the programmers, not thinking enough
about precision - and the result of this thought process is usually the
elimination, not of truncation/rounding, but of not accounting for these
errors. Which, to me, equates to "eliminating those pesky floating point
errors".

Although to be more accurate I should have said "eliminates those pesky
programmer errors when dealing with floating point arithmetic."

apoligetically,
Wayne
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