[SciPy-Dev] Change the return of ndimage functions

[Ralf Gommers]

On Thu, Feb 22, 2018 at 12:36 PM, Jaime Fernández del Río <
jaime.frio at gmail.com> wrote:

> Hi,
>
> For some odd reason, several ndimage functions only return the output
> array if it has been allocated by the function itself, not if you have
> passed a preallocated array to the function, e.g.:
>
> ndimage.correlate1d([1, 2, 3], [1, 1, 1])  # returns [4, 6, 8]
>
> out = np.empty(3)
> ndimage.correlate1d([1, 2, 3], [1, 1, 1], output=out)  # returns None (but
> writes [4, 6, 8] to out)
>
>
> I find this to be an annoying, unintuitive behaviour, that differs from
> what e.g. numpy ufuncs do, and that often requires special handling, see
> e.g. the review comments in #8455
> <https://github.com/scipy/scipy/pull/8455>. It is furthermore not
> consistently implemented, as several functions do return the output array
> always.
> I have submitted #8461 <https://github.com/scipy/scipy/pull/8461>
> changing this behaviour so that the output array is always returned,
> regardless if it was given by the user or allocated by the function. It
> probably says more about the poor coverage of the tests than anything else,
> but the change did not make any of the current tests fail.
>
> I doubt this change will be problematic to any user, but it is indeed a
> change to a longstanding, documented behavior, so it probably deserves more
> discussion than would happen in the PR alone. Any objections anyone?
>

Makes sense to me, no objections.

Cheers,
Ralf
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