Type conversion of octave_value to/from Python representations

[John W. Eaton]

On 18-Sep-2008, David Grundberg wrote:

| I'm having trouble with creating any octave-value with a dimension 
| higher than 3, how do I do that?

Create an NDArray using a dim_vector object to specify the
dimensions.

| *Converting octave-value:s to Python objects*
| 
| This is when I really got stuck. I'm having trouble figuring out how to 
| properly access the actual storage type (Array<T> subclass, or 
| primitive, or?). I'm doing this right now (kind of):
| 
| octave_value ov = fromsomewhere;
| if (ov.is_bool_scalar)) {
|     pyobj = object(ov.bool_value());
| } if // etc..
| } else if (ov.is_matrix_type()) { // try to convert to numeric array
|     if (ov.is_nd_real_array()) {
|        // Try to use instantiate an NDArray with octave-value-argument 
| constructor
|     }
|     else if (ov.is_double_type()) {
|        // Try to use instantiate a Matrix with octave-value-argument 
| constructor
|     }
| }
| 
| And this won't work, since octave-values with NDArray:s won't return 
| true on is_nd_real_array(). The Matrix(ov) constructor won't accept a 3d 
| real ov either. ("fatal: invalid conversion of NDArray to Matrix")

Doesn't something like

  if (ov.is_single_type ())
    {
      if (ov.is_complex_type ())
        {
          FloatComplexNDArray tmp = ov.float_complex_array_value ();
          ...
        }
      else if (ov.is_real_type ())
        {
          FloatNDArray tmp = ov.float_array_value ();
          ...
        }
      else
        error (???);
     }
   else if (ov.is_double_type ())
    {
      if (ov.is_complex_type ())
        {
          ComplexNDArray tmp = ov.complex_array_value ();
          ...
        }
      else if (ov.is_real_type ())
        {
          NDArray tmp = ov.array_value ();
          ...
        }
      else
        error (???);
     }
   else ...

work?  I'm assuming you are working with the development version of
Octave, which has the single type.  Does Python have single precision
numeric values?

| Oh, there is so much wrong with this type of checking, I don't know 
| where to begin.

Pick a spot and start griping, I guess.

How would you like to be able to write this conversion?

jwe