[Python-Dev] Symmetry arguments for API expansion

[David Mertz]

On Mon, Mar 12, 2018, 3:25 PM Tim Peters <tim.peters at gmail.com> wrote:

> [David Mertz <mertz at gnosis.cx>]
> > ...
> > I can see no sane reason why anyone would ever call float.is_integer()
> > actually. That should always be spelled math.isclose(x, int(x)) because
> > IEEE-754. Attractive nuisance is probably too generous, I'd simply call
> the
> > method a bug.
>
> Sometimes it's necessary to know, and especially when _implementing_
> 754-conforming functions.  For example, what negative infinity raised
> to a power needs to return depends on whether the power is an integer
> (specifically on whether it's an odd integer):
>
> >>> (-math.inf) ** 3.1
> inf
>

Weird. I take it that's what IEEE-754 says. NaN would sure be more
intuitive here since inf+inf-j is not in the domain of Reals. Well,
technically neither is inf, but at least it's the limit of the domain. :-).

>>> (-math.inf) ** 3.0 # NOTE THIS ONE
> -inf
> >>> (-math.inf) ** 2.9
> inf
>
> But, ya, for most people most of the time I agree is_integer() is an
> attractive nuisance.  People implementing math functions are famous
> for cheerfully enduring any amount of pain needed to get the job done
> ;-)
>
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