On Wed, Nov 24, 2021 at 3:04 AM ast <ast@invalid> wrote: > > Le 19/11/2021 à 21:17, Chris Angelico a écrit : > > On Sat, Nov 20, 2021 at 5:08 AM ast <ast@invalid> wrote: > >> > >> Le 19/11/2021 à 03:51, MRAB a écrit : > >>> On 2021-11-19 02:40, 2qdxy4rzwzuui...@potatochowder.com wrote: > >>>> On 2021-11-18 at 23:16:32 -0300, > >>>> René Silva Valdés <rene.silva.val...@gmail.com> wrote: > >>>> > > >> > >> >>> 0.3 + 0.3 + 0.3 == 0.9 > >> False > > > > That's because 0.3 is not 3/10. It's not because floats are > > "unreliable" or "inaccurate". It's because the ones you're entering > > are not what you think they are. > > > > When will people understand this? > > > > (Probably never. Sigh.) > > > > ChrisA > > > > I posted that to make people aware of danger of float comparison, > not because I was not understanding what happened.
And I posted to show that equality is not the problem, and that float comparison is not dangerous. > We can see there is a difference on the lsb, due to rounding. > > >>> (0.3+0.3+0.3).hex() > '0x1.cccccccccccccp-1' > >>> 0.9.hex() > '0x1.ccccccccccccdp-1' > >>> > > An isclose() function is provided in module math to do float > comparison safely. > > >>> math.isclose(0.3+0.3+0.3, 0.9) > True This is why isclose() was so controversial: it is very very easy to misuse it. Like this. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
