Author Carlos Neves
Recipients Carlos Neves, lemburg, mark.dickinson, rhettinger, stutzbach, tim.peters
Date 2020-07-02.21:45:37
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Content
Hi Peters,

I will pay more attention to the Python docs :)
Thank you for your direction.

Carlos A. Neves

Em qui., 2 de jul. de 2020 às 18:22, Tim Peters
<report@bugs.python.org> escreveu:
>
>
> Tim Peters <tim@python.org> added the comment:
>
> For the first, your hardware's binary floating-point has no concept of significant trailing zeroes. If you need such a thing, use Python's `decimal` module instead, which does support a "significant trailing zero" concept. You would need an entirely new data type to graft such a notion onto Python's (or numpy's!) binary floats.
>
> For the second, we'd have to dig into exactly what numpy's `arange()` does. Very few of the numbers you're working with are exactly representable in binary floating point except for 0.0. For example, "0.001" is approximated by a binary float whose exact decimal value is
>
> 0.001000000000000000020816681711721685132943093776702880859375
>
> Sometimes the rounded (by machine float arithmetic) multiples of that are exactly representable, but usually not. For example,
>
> >>> 0.001 * 250
> 0.25
>
> rounds to the exactly representable 1/4, and
>
> >>> 0.001 * 750
> 0.75
>
> to the exactly representable 3/4. However, `round()` uses round-to-nearest/even, and then
>
> >>> round(0.25, 1)
> 0.2
> >>> round(0.75, 1)
> 0.8
>
> both resolve the tie to the closest even value (although neither of those _results_ are exactly representable in binary floating-point - although if you go on to multiply them by 10.0, they do round (in hardware) to exactly 2.0 and 8.0).
>
> Note that numpy's arange() docs do warn you against using it ;-)
>
> """
> When using a non-integer step, such as 0.1, the results will often not be consistent. It is better to use numpy.linspace for these cases.
> """
>
> ----------
> nosy: +tim.peters
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue41198>
> _______________________________________
History
Date User Action Args
2020-07-02 21:45:37Carlos Nevessetrecipients: + Carlos Neves, lemburg, tim.peters, rhettinger, mark.dickinson, stutzbach
2020-07-02 21:45:37Carlos Neveslinkissue41198 messages
2020-07-02 21:45:37Carlos Nevescreate