[Numpy-discussion] NEP 21: Simplified and explicit advanced indexing (original) (raw)

Robert Kern robert.kern at gmail.com
Tue Jun 26 21:38:44 EDT 2018

On Tue, Jun 26, 2018 at 6:14 PM Stephan Hoyer <shoyer at gmail.com> wrote:

On Tue, Jun 26, 2018 at 4:34 PM Robert Kern <robert.kern at gmail.com> wrote:

I maintain that considering deprecation is premature at this time. Please take it out of this NEP. Let us get a feel for how people actually use .oindex/.vindex. Then we can talk about deprecation. This NEP gets my enthusiastic approval, except for the deprecation. I will be happy to talk about deprecation with an open mind in a few years. With some more actual experience under our belt, rather than prediction and theory, we can be more confident about the approach we want to take. Deprecation is not a fundamental part of this NEP and can be decided independently at a later time.

I agree, we should scale back most of the deprecations proposed in this NEP, leaving them for possible future work. In particular, you're not convinced yet that "outer indexing" is a more intuitive default indexing mode than "vectorized indexing", so it is premature to deprecate vectorized indexing behavior that conflicts with outer indexing. OK, fair enough.

Actually, I do think outer indexing is more "intuitive"*, as far as that goes. It's just rarely what I actually want to accomplish.

I would still like to include at least two more limited form of deprecation

that I hope will be less controversial: - Mixed boolean/integer array indexing. This is not very intuitive nor useful, and I don't think I've ever seen it used. Usually "outer indexing" behavior is what is desired here. - Mixed array/slice indexing, for cases with arrays separated by slices so NumPy can't do the "intuitive" transpose on the output. As noted in the NEP, this is a common source of bugs. Users who want this should really switch to vindex.

I'd still prefer not talking deprecation, per se, in this NEP (but my objection is weaker). I would definitely start adding in informative, noisy warnings in these cases, though. Along the lines of, "Hey, this is a dodgy construction that typically gives unexpected results. Here are .oindex/.vindex that might do what you actually want, but you can use .legacy_index if you just want to silence this warning". Rather than "Hey, this is going to go away at some point."

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