Hence why I said 'would', 'if' etc. And it was brought up/suggested, having
singletons. It does naturally flow from having a built-in (much like having
singletons for booleans does):
sugggesting that one reason that they were made keywords is that it's
> useful for them to be singletons, which is much harder to do (or at least
> use consistently) if the names can be reassigned.
> But these float special values can't be singletons anyway -- they could
> come from anywhere, so you really don't want to have people doing:
>
(to be honest, to me it does make sense to have 'inf' singletons, but not
for 'nan's. but, neither is part of the PEP).
'inf' is a very special value, and there are only 2 infinite floats (inf,
-inf).
Having a singleton is useful also perhaps as a memory optimization (i.e.
whenever creating a float from C, check if it is infinite, and if so,
return a new reference to the global inf/-inf variable).
Again, this is not part of the PEP, so I don't think we want to spend much
time discussing whether they should be singletons. For now, the answer
seems to be: no
Thanks,
----
*Cade Brown*
Research Assistant @ ICL (Innovative Computing Laboratory)
Personal Email: brown.c...@gmail.com
ICL/College Email: c...@utk.edu
On Sun, Sep 13, 2020 at 10:19 PM Chris Angelico <ros...@gmail.com> wrote:
> On Mon, Sep 14, 2020 at 11:05 AM Cade Brown <brown.c...@gmail.com> wrote:
> > This would become relevant, if, say Python 4.0 migrated 'inf' and 'nan'
> to builtin names (like True and False). If that happened, a 'nan' singleton
> wouldn't make sense unless you had 2**53 of them, so code like:
> >
> > >>> x is nan
> >
> > Would be a flawed formulation
> >
>
> Nobody's suggesting that they become keywords representing singletons,
> which is what True and False are. (At least, I don't think so.) What's
> being proposed is simply a builtin name that has a value of
> float("inf"). People don't write "x is 1.5" and they shouldn't use "x
> is inf". It doesn't matter that there are multiple bit patterns that
> represent nan; you shouldn't be doing this even when there's only one
> bit pattern for the value. Yes, sometimes people do this with small
> integers, and in CPython it may work ("x is 5" will usually be true
> for any integer 5), but it's just as buggy there and I don't think
> that's particularly relevant.
>
> (How often do people even use "x is True"?)
>
> ChrisA
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