Wrap C struct with array member for access in python: SWIG? cython? ctypes?

Question

I want to access a C function that returns a struct containing double arrays (where the lengths of these arrays is given by other int members of the struct) from python. The dec

Answer 1

An equivalent to the SWIG created module using ctypes looks as follows:

from ctypes import *
from numpy import *

lib = cdll.LoadLibrary("_get_element.so")

class ELEMENT(Structure):
    _fields_ = [("dim", c_int),
                ("vertices", c_int),
                ("quadrature_degree", c_int),
                ("polynomial_degree", c_int),
                ("ngi", c_int),
                ("quadrature_familiy", c_int),
                ("weight", POINTER(c_double)),
                ("l", POINTER(c_double)),
                ("n", POINTER(c_double)),
                ("dn", POINTER(c_double))]

cget_element = lib.get_element
cget_element.argtypes = [c_int, c_int, c_int, c_int, POINTER(ELEMENT)]
cget_element.restype = None

def get_element(dim, vertices, quad_degree, poly_degree):
    e = ELEMENT()
    cget_element(dim, vertices, quad_degree, poly_degree, byref(e))
    weight = asarray([e.weight[i] for i in xrange(e.ngi)], dtype=float64)
    l = asarray([e.l[i] for i in xrange(e.ngi*e.dim)], dtype=float64).reshape((e.ngi,e.dim))
    n = asarray([e.n[i] for i in xrange(e.ngi*e.vertices)], dtype=float64).reshape((e.ngi,e.vertices))
    dn = asarray([e.dn[i] for i in xrange(e.ngi*e.vertices*e.dim)], dtype=float64).reshape((e.ngi,e.vertices,e.dim))
    return weight, l, n, dn