Matt, What's happening is the 'npy_type' is not getting set for each call of 'run_validators()' because it is set under the same 'if' statement that creates the initial array to store the values in. Subsequent calls don't create the array, but they also don't set 'npy_type'. So I think this: if(pv->return_values[i] == NULL){ should be moved to surround: pv->return_values[i] = (PyArrayObject *) PyArray_SimpleNewFromDescr( 1, &dims, PyArray_DescrFromType(npy_type)); Or, 'npy_type' needs to be stored more persistently between calls of 'run_validators()'. Thoughts? _______________________________________________________ sskory@physics.ucsd.edu o__ Stephen Skory http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student ________________________________(_)_\(_)_______________