Python, GDAL and building raster attribute tables

The SetValueAsInt method is expecting a python int type, not a numpy uint16 type.

>>> print type(vals[0])
<type 'numpy.uint16'>

The following works:

rat.SetValueAsInt(i, 0, int(vals[i]))

If you use vals = numpy.unique(data).tolist() instead it will automatically convert each value to a python int type.