[Python-ideas] Re: PEP 472 - slices in keyword indices, d[x=1:3]

On Tue, Aug 25, 2020 at 10:58 AM David Mertz wrote:

On Tue, Aug 25, 2020 at 2:26 AM Christopher Barker wrote:

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As for "why not" not being a motivator -- I agree, I posted it that easy because this conversation has brought up a number of examples where slice syntax is nice to use. And David Mertz pointed out, both numpy and pandas have a utility to make easier slices -- yes, that's an argument for why you don't need them, but it's also an argument for why there IS a need for slice objects outside of the square brackets, and if we need slice objects, then slice syntax is nice.

Pandas is kinda special though. It semi-abuses Python syntax in quite a few places. For example, here is an example from the Pandas docs:

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idx = pd.IndexSlice>>> dfmi.loc[idx[:, 'B0':'B1'], :]

There is a hierarchical index (MultiIndex) where we want to put slices as some of the "dimensions" of slice items. It definitely makes sense in the Pandas world, but I have never once encountered anywhere I would want "stand-alone" slice objects outside of Pandas. I know NumPy includes the same convenience, but it's not even coming to me immediately in what context you would want that in NumPy.

I had to do it in a situation where I needed slices but couldn't tell ahead of time how many dimensions would be sliced. So I had to construct a dynamically-sized tuple of slices on-the-fly. I doubt this is not a common situation, though.