[Python-ideas] slice[] to get more complex slices

[David Mertz]

I find pandas.IndexSlice makes a lot of operations easier to spell. As
simple as it is, it's a valuable capability. Rather than every library—or a
number of them anyway—creating the same 4 lines of code with a different
name, it would be much nicer to have it as a class __getitem__ method, e.g.
slice[...], or as an attribute of the slice object, such as
slice.literal[...].

On Mon, Jul 23, 2018, 7:20 PM Stefan Behnel <stefan_ml at behnel.de> wrote:

> Stephan Hoyer schrieb am 23.07.2018 um 18:01:
> > On Mon, Jul 23, 2018 at 4:24 AM Paul Moore wrote:
> >
> >> I thought the reason the proposal got nowhere was because it's pretty
> >> simple to define it yourself:
> >>
> >> >>> class SliceHelper:
> >> ...     def __getitem__(self, slice):
> >> ...         return slice
> >> ...
> >> >>> SH = SliceHelper()
> >> >>> SH[1::3]
> >> slice(1, None, 3)
> >>
> >> Did I miss something significant about why this wasn't sufficient?
> >
> >
> > I think a SliceHelper class like this is a reasonable solution, but there
> > would be a lot of value having it a standard place somewhere in the
> > standard library (e.g., operator.subscript).
> >
> > Both pandas and NumPy include this helper object under different names
> > (pandas.IndexSlice and numpy.index_exp / numpy.s_), but it would be
> > surprising/unexpected for pandas/numpy specific helpers to show up when
> not
> > using one of those libraries. I do the exact same sorts of indexing
> > manipulations with xarray, dask and TensorFlow.
> >
> > Given that this is basically a simple feature to make it easier to work
> > with Python syntax (so there's no danger it will change in the future), I
> > think there is a lot to be said for putting it in the standard library in
> > one place so it's obvious what to use and users don't have to relearn
> that
> > name for this object and/or reimplement it.
>
> Please copy that comment into the ticket and ask for it to be reopened.
>
> https://bugs.python.org/issue24379
>
> Stefan
>
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