[Numpy-discussion] NEP 30 - Duck Typing for NumPy Arrays - Implementation

[Ralf Gommers]

On Mon, Aug 5, 2019 at 6:18 PM Stephan Hoyer <shoyer at gmail.com> wrote:

> On Mon, Aug 5, 2019 at 2:48 PM Ralf Gommers <ralf.gommers at gmail.com>
> wrote:
>
>
>> The NEP currently does not say who this is meant for. Would you expect
>> libraries like SciPy to adopt it for example?
>>
>> The NEP also (understandably) punts on the question of when something is
>> a valid duck array. If you want this to be widely used, that will need an
>> answer or at least some rough guidance though. For example, we would expect
>> a duck array to have a mean() method, but probably not a ptp() method. A
>> library author who wants to use np.duckarray() needs to know, because she
>> can't test with all existing and future duck array implementations.
>>
>
> I think this is covered in NEP-22 already.
>

It's not really. We discussed this briefly in the community call today,
Peter said he will try to add some text.

We should not add new functions to NumPy without indicating who is supposed
to use this, and what need it fills / problem it solves. It seems pretty
clear to me that it's mostly aimed at library authors rather than end
users. And also that mature libraries like SciPy may not immediately adopt
it, because it's too fuzzy - so it's new libraries first, mature libraries
after the dust has settled a bit (I think).

As discussed there, I don't think NumPy is in a good position to pronounce
> decisive APIs at this time. I would welcome efforts to try, but I don't
> think that's essential for now.
>

There's no need to pronounce a decisive API that fully covers duck array.
Note that RNumPy is an attempt in that direction (not a full one, but way
better than nothing). In the NEP/docs, at least saying something along the
lines of "if you implement this, we recommend the following strategy: check
if a function is present in Dask, CuPy and Sparse. If so, it's reasonable
to expect any duck array to work here. If not, we suggest you indicate in
your docstring what kinds of duck arrays are accepted, or what properties
they need to have". That's a spec by implementation, which is less than
ideal but better than saying nothing.

Cheers,
Ralf
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