There have been a number of discussions on this list, and at least one PEP, about NaN (and other special values).
Let’s keep this thread about handling them in the statistics lib. But briefly: NaNs are weird on purpose, and Python should absolutely not deviate from IEEE. That’s (one reason) Python has None :-) If you are that worried about performance, you should probably use numpy anyway :-) -CHB On Thu, Aug 26, 2021 at 3:47 AM Marc-Andre Lemburg <m...@egenix.com> wrote: > On 26.08.2021 12:15, Steven D'Aprano wrote: > > On Thu, Aug 26, 2021 at 11:05:01AM +0200, Marc-Andre Lemburg wrote: > > > >> Oh, good point. I was under the impression that NAN is handled > >> as a singleton. > > > > There are 4503599627370496 distinct quiet NANs (plus about the same > > signalling NANs). So it would need to be 4-quadrillion-ton :-) > > > > (If anyone is concerned about the large number of NANs, it's less than > > 0.05% of the total number of floats.) > > > > Back in the mid-80s, Apple's floating point library, SANE, distinguished > > different classes of error with distinct NANs. Few systems have followed > > that lead, but each NAN still has 51 bits available for a diagnostic > > code, plus the sign bit. While Python itself only generates a single NAN > > value, if you are receiving data from outside sources it could contain > > NANs with distinct payloads. > > > > The IEEE-754 standard doesn't mandate that NANs preserve the payload, > > but it does recommend it. We shouldn't gratuitously discard that > > information. It could be meaningful to whoever is generating the data. > > Fair enough. Would it then make sense to at least have all possible > NAN objects compare equal, treating the extra error information as an > attribute value rather than a distinct value and perhaps exposing this > as such ? > > I'm after the "practicality beats purity" here. The math.isnan() test > doesn't work well in practice, since you'd have to iterate over all > sequence members and call that test function, which is expensive when > done in Python. > > -- > Marc-Andre Lemburg > eGenix.com > > Professional Python Services directly from the Experts (#1, Aug 26 2021) > >>> Python Projects, Coaching and Support ... https://www.egenix.com/ > >>> Python Product Development ... https://consulting.egenix.com/ > ________________________________________________________________________ > > ::: We implement business ideas - efficiently in both time and costs ::: > > eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 > D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg > Registered at Amtsgericht Duesseldorf: HRB 46611 > https://www.egenix.com/company/contact/ > https://www.malemburg.com/ > > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/GX7PAY5ZR76KBK5INWKV2Y67FKCCAK2Y/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- Christopher Barker, PhD (Chris) Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython
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