[Numpy-discussion] Proposal to make power return float, and other such things.

[Robert Kern]

On Tue, Feb 18, 2014 at 2:37 PM,  <josef.pktd at gmail.com> wrote:
> On Tue, Feb 18, 2014 at 8:53 AM, Robert Kern <robert.kern at gmail.com> wrote:
>> On Tue, Feb 18, 2014 at 1:46 PM, Nathaniel Smith <njs at pobox.com> wrote:
>>> On 18 Feb 2014 07:07, "Robert Kern" <robert.kern at gmail.com> wrote:
>>>>
>>>> On Tue, Feb 18, 2014 at 12:00 PM, Nathaniel Smith <njs at pobox.com> wrote:
>>>> > Perhaps integer power should raise an error on negative powers? That way
>>>> > people will at least be directed to use arr ** -1.0 instead of silently
>>>> > getting nonsense from arr ** -1.
>>>>
>>>> Controllable by np.seterr(invalid=...)? I could get behind that.
>>>
>>> I'm not sure the np.seterr part would work or be a good idea, given that we
>>> have no way to return or propagate NaN... I vote for just an unconditional
>>> error.
>>
>> <shrug> We issue configurable warning/error/ignore behavior for
>> integer 0/0 through this mechanism too without any NaNs. However,
>> that's `divide` and not `invalid`. Your point is taken that `invalid`
>> usually implies that a `NaN` is generated, though I don't think this
>> is ever stated anywhere. I just suggested `invalid` as that is usually
>> what we use for function domain violations.
>
> I thought 0/0 = 0 has been removed a few versions ago. Does numpy
> still have silent casting of nan to 0 in ints.

There is no casting involved.

> I thought invalid and divide error/warnings are for floating point
> when we want to signal that the outcome is nan or inf, not that we are
> casting and return a result that is just wrong.

No, they are also for some integer operations without going through a
floating point intermediate.

-- 
Robert Kern