[Numpy-discussion] New Indexing Methods Revival #N (subclasses!)

[Sebastian Berg]

Hi all,

not that I am planning to spend much time on this right now, however, I
did a small rebase of the stuff I had (did not push yet) on oindex and
remembered the old problem ;).

The one remaining issue I have with adding things like (except making
the code prettier and writing tests):

arr.oindex[...]  # outer/orthogonal indexing
arr.vindex[...]  # Picking of elements (much like current)
arr.lindex[...]  # current behaviour for backward compat

is what to do about subclasses. Now what I can do (and have currently
in my branch) is to tell someone on `subclass.oindex[...]`: This won't
work, the subclass implements `__getitem__` or `__setitem__` so I don't
know if the result would be correct (its a bit annoying if you also
warn about using those attributes, but...).

However, with or without such error, we need a nice way for subclasses
to define these attributes! This is important even within numpy at
least for masked arrays (possibly also matrix and memmap).

They (typically) do some stuff before or after the plain indexing
operation, so how do we make it convenient to allow them to do the same
stuff for the special indexing attributes without weird code
duplication? I can think of things, but nothing too great yet so maybe
you guys got an elegant idea.

- Sebastian
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