[Numpy-discussion] Prep for NumPy 1.16.0 branch

[Stephan Hoyer]

On Sun, Nov 4, 2018 at 10:32 AM Marten van Kerkwijk <
m.h.vankerkwijk at gmail.com> wrote:

> Hi Chuck,
>
> For `__array_function__`, there was some discussion in
> https://github.com/numpy/numpy/issues/12225 that for 1.16 we might want
> to follow after all Nathaniel's suggestion of using an environment variable
> or so to opt in (since introspection breaks on python2 with our wrapped
> implementations).  Given also the possibly significant hit in performance,
> this may be the best option.
> All the best,
>
> Marten
>

I am also leaning towards this right now, depending on how long we plan to
wait for releasing 1.16. It will take us at least a little while to sort
out performance issues for __array_function__, I'd guess at least a few
weeks. Then a blocker still might turn up during the release candidate
process (though I think we've found most of the major bugs / downstream
issues already through tests on NumPy's dev branch).

Overall, it does feels a little misguided to rush in a change as pervasive
as __array_function__ for a long term support release. If we exclude
__array_function__ I expect the whole release process for 1.16 would go
much smoother. We might even try to get 1.17 out faster than usual, so we
can minimize the number of additional changes besides __array_function__
and going Python 3 only -- that's already a good bit of change.

Note that if we make this change (reverting __array_function__), we'll need
to revisit where we put a few deprecation warnings -- these will need to be
restored into function bodies, not their dispatcher functions.

Also: it would be really nice if we get matmul-as-ufunc in before (or at
the same time) as __array_function__, so we have a complete story about it
being possible to override everything in NumPy. This is another argument
for delaying __array_function__, if matmul-as-ufunc can't make it in time
for 1.16.

Best,
Stephan
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