[ctypes-users] Functions returning a Struct

[<wr...@hu...>]

I was attempting to learn ctypes by wrapping several functions from libgls.
Everything was working smoothly until I got several functions that
returned structures. the c code looked like this:
typedef struct
  {
    double dat[2];
  }
gsl_complex;

gsl_complex gsl_complex_rect (double x, double y)
{                               /* return z = x + i y */
  gsl_complex z;
  GSL_SET_COMPLEX (&z, x, y);
  return z;
}
#GSL_SET_COMPLEX is a macro defined as
#define GSL_SET_COMPLEX(zp,x,y) do {(zp)->dat[0]=(x); (zp)->dat[1]=(y);}
while(0)

I tried to access this function with the following python code:
import ctypes
gsl = ctypes.cdll.libgsl
class gsl_complex(ctypes.Structure):
    _fields_ = [("dat", ctypes.c_double*2)]

gsl_complex_rect = gsl.gsl_complex_rect
gsl_complex_rect.argtypes = [ctypes.c_double, ctypes.c_double]
gsl_complex_rect.restype = gsl_complex
arg1 = ctypes.c_double(1.2)
arg2 = ctypes.c_double(3.4)
complex_num = gsl_complex_rect(arg1, arg2)

this results in an exception:
ValueError: Procedure called with not enough arguments (4 bytes missing)
or wrong calling convention
The arguments seem to be correct, and I successfully called other
functions with this calling convention.
changing to stdcall or windll did not fix the problem.
Any suggestions? Thanks in advance, Wilton