at.get_value_refpts fails if the field value is scalar and an index 0 is provided

[simoneliuzzo]

get_value_refpts(ring, array_of_indexes, 'PolynomB', 0)
works, giving the first element of PolynomB for the elements of ring with indexes in array_of_indexes.

get_value_refpts(ring, array_of_indexes, 'Length', 0)
instead fails, as Length is a scalar.

I had this second line in my code, the index 0 being there from copy-paste. I did not expect it to fail, Length has length 1, so index 0 did not seem to be possibly generating an error.

The help of get_value_refpts says it: " ... IF attr_name is an array"

I find this somehow strange that the user has to remember if the specific attribute is an array or not when using the command get_value_refpts.

The error message is a python error and it is not very immediate. It could be caught and translated to a warning. For example: "For scalar attributes index is ignored".

This action, would also recover a usage similar to the matlab equivalent of this function atgetfieldvalues, that does not fail in the case atgetfieldvalues(r, ind, 'Length', 0).

[lfarv]

@simoneliuzzo:

Unlike in Matlab, scalar and numpy arrays are completely different python objects ! You indeed need to know what is the attribute. But I doubt that you would extract attribute values without knowing what they mean…

Anyway, I very much prefer using a simple python command rather that using get_value_refpts: in your example, you would write

b0=[elem.PolynomB[0] for elem in ring.select(array_of_indexes)]

or

lengths=[elem.Length for elem in ring.select(array_of_indexes)]

It's more efficient, it works for integer or boolean indices (get_value_refpts also, of course) and it's self-explanatory for a python developer… The function does not bring anything, but it's a matter of taste.