Carlos Neves <cane...@gmail.com> added the comment: 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 <rep...@bugs.python.org> escreveu: > > > Tim Peters <t...@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 <rep...@bugs.python.org> > <https://bugs.python.org/issue41198> > _______________________________________ ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue41198> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
