On 5 Apr 2013, at 19:38, James Stroud wrote:

Hu Luc,

On Apr 5, 2013, at 6:46 AM, Luc Bourhis wrote:
However, we haven't address the important question: what behaviour do we really want?
(i) the numpy array and the flex array must have the same element type, and an exception is thrown if this precondition is violated;
(ii) we use a fast copy of the numpy array to the flex array if the element types are the same; otherwise we fall back to a slower conversion.

My understanding of the "python way" would be that the desired behavior is (ii). [...]

Good demonstration: I fully agree with you. We will try to implement (ii) then.

Taking the "pythonic" approach only requires

http://docs.scipy.org/doc/numpy/reference/c-api.array.html#PyArray_CastToType

For each of the element types that could comprise flex arrays, one only needs to write one PyArray_Descr

http://docs.scipy.org/doc/numpy/reference/c-api.types-and-structures.html#PyArray_Descr

which becomes the second argument for PyArray_CastToType.

Unfortunately the real difficulty is that a flex array does not have a descriptor as a numpy array does. In some sense the latter does not know the type of its elements: only the C++ compiler does. Thus some template trickery is still needed to map the each numpy array element type to the right flex element type.