Making indexing more strict?

[seberg]

As per my comment here

Beyond "why not", I wonder if there is even a point in allowing arr[boolean_index,] as opposed to just arr[boolean_index].

I admit, since it does not preclude arr_nd[boolean_index_1d, ...] it probably doesn't matter. On the other hand, it seems unnecessary to force arra-likes to implement it. It seems fine for an object to define arr_nd[boolean_index_1d, ...], but regard arr_nd[boolean_index_nd,] as malformed (because it indexes dimension 1 with an N-D index, rather than a 1-D one).

And here about SymPy's way of indexing a Matrix

I don't really agree that SymPy matrices are super weird. I quite like the way they think about elements rather than dimensional indexing. And I think especially with respect to __len__ and __iter__ it would make sense to only strictly define arr_1d[integer] and but not arr_2d[integer]. The latter can be spelled explicitly using arr_2d[integer, ...] or arr_2d[integer, :] which is much more clear and unambiguous. (even arr_2d[integer,] is fine in theory.)

The "downside" is that you don't try to copy the python lists-of-lists analogy. But I am not sure its a particularly good one in any case?

[rgommers]

Missing a bit of context/knowledge on SymPy here, so can't comment on everything - but definitely agree with not allowing arr_2d[integer]!

The "downside" is that you don't try to copy the python lists-of-lists analogy. But I am not sure its a particularly good one in any case?

Agree, not much of a downside.

[seberg]

Just for reference on SymPy:

In [3]: m = sympy.Matrix([[1, 2], [3, 4]])

In [4]: m[0]
Out[4]: 1

In [5]: list(m)  # via __iter__
Out[5]: [1, 2, 3, 4]

SymPy does flat indexing for a single integer index, since it does flat iteration.

[rgommers]

(even arr_2d[integer,] is fine in theory.)

I think what we'd like is to make indexing unambiguous. Which means (to me at least) to specify an index for all axes with some valid method (integer, slice, ellipsis). Both arr_2d[integer] and arr_2d[integer,] fail to do that, so I think if we forbid one we should forbid both of those forms.

SymPy does flat indexing for a single integer index, since it does flat iteration.

I guess we'd want that spelled reshape(x, (-1,))[integer]