int func(a * aa, b * bb, c * cc);

typedef struct
{
        int              a1;
}a;

typedef struct
{
        int              b1;
        unsigned char    *b2;

}b;

typedef struct
{
        int              c1;
        unsigned char    *c2;
}c;

func.argtypes = (ctypes.POINTER(a),
                    ctypes.POINTER(b),
                    ctypes.POINTER(c))
func.restype=ctypes.c_int
status=dll.func(aa,bb,cc)

ValueError: ctypes objects containing pointers cannot be pickled