[Numpy-discussion] Numpy integers to integer powers again again

[Nathaniel Smith]

On Mon, Oct 24, 2016 at 3:41 PM, Charles R Harris
<charlesr.harris at gmail.com> wrote:
> Hi All,
>
> I've been thinking about this some (a lot) more and have an alternate
> proposal for the behavior of the `**` operator
>
> if both base and power are numpy/python scalar integers, convert to python
> integers and call the `**` operator. That would solve both the precision and
> compatibility problems and I think is the option of least surprise. For
> those who need type preservation and modular arithmetic, the np.power
> function remains, although the type conversions can be surpirising as it
> seems that the base and power should  play different roles in determining
> the type, at least to me.
> Array, 0-d or not, are treated differently from scalars and integers raised
> to negative integer powers always raise an error.
>
> I think this solves most problems and would not be difficult to implement.
>
> Thoughts?

My main concern about this is that it adds more special cases to numpy
scalars, and a new behavioral deviation between 0d arrays and scalars,
when ideally we should be trying to reduce the
duplication/discrepancies between these. It's also inconsistent with
how other operations on integer scalars work, e.g. regular addition
overflows rather than promoting to Python int:

In [8]: np.int64(2 ** 63 - 1) + 1
/home/njs/.user-python3.5-64bit/bin/ipython:1: RuntimeWarning:
overflow encountered in long_scalars
  #!/home/njs/.user-python3.5-64bit/bin/python3.5
Out[8]: -9223372036854775808

So I'm inclined to try and keep it simple, like in your previous
proposal... theoretically of course it would be nice to have the
perfect solution here, but at this point it feels like we might be
overthinking this trying to get that last 1% of improvement. The thing
where 2 ** -1 returns 0 is just broken and bites people so we should
definitely fix it, but beyond that I'm not sure it really matters
*that* much what we do, and "special cases aren't special enough to
break the rules" and all that.

-n

-- 
Nathaniel J. Smith -- https://vorpus.org