[Numpy-discussion] SWIG wrappers: Inplace arrays

Travis Oliphant oliphant at ee.byu.edu
Tue Apr 25 16:07:05 CDT 2006


Albert Strasheim wrote:

>Hello all
>
>I am using the SWIG Numpy typemaps to wrap some C code. I ran into the
>following problem when wrapping a function with INPLACE_ARRAY1.
>
>In Python, I create the following array:
>
>x = array([],dtype='<i4')
>
>When this is passed to the C function expecting an int*, it goes via
>obj_to_array_no_conversion in numpy.i where a direct comparison of the
>typecodes is done, at which point a TypeError is raised.
>
>In this case:
>
>desired type = int [typecode 5]
>actual type = long [typecode 7]
>
>The typecode is obtained as follows:
>
>#define array_type(a) (int)(((PyArrayObject *)a)->descr->type_num)
>
>Given that I created the array with '<i4', I would expect type_num to map to
>int instead of long. Why isn't this happening?
>
>Assuming the is a good reason for type_num being what it is, I think
>obj_to_array_no_conversion needs to be slightly cleverer about the
>conversions it allows. Is there any way to figure out that int and long are
>actually identical (at least on my system) using the Numpy C API? Any other
>suggestions or comments for solving this problem?
>
>  
>
Here is the relevant new numpy.i code (just checked in...)

PyArrayObject* obj_to_array_no_conversion(PyObject* input, int typecode) {
  PyArrayObject* ary = NULL;
  if (is_array(input) && (typecode == PyArray_NOTYPE ||
        PyArray_EquivTypenums(array_type(input), typecode)) {
        ary = (PyArrayObject*) input;
    }
    else if is_array(input) {
      char* desired_type = typecode_string(typecode);
      char* actual_type = typecode_string(array_type(input));
      PyErr_Format(PyExc_TypeError,
                   "Array of type '%s' required.  Array of type '%s' given",
                   desired_type, actual_type);
      ary = NULL;
    }
    else {
      char * desired_type = typecode_string(typecode);
      char * actual_type = pytype_string(input);
      PyErr_Format(PyExc_TypeError,
                   "Array of type '%s' required.  A %s was given",
                   desired_type, actual_type);
      ary = NULL;
    }
  return ary;
}





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