#include <Python.h>

typedef struct
{
    PyObject_HEAD;
    double data[3];
} vector3d;

static PyObject* vector3d_new(PyTypeObject* type, PyObject* args, PyObject* kwds)
{
    vector3d* self;
    self = (vector3d*)type->tp_alloc(type, 0);

    self->data[0]=0;
    self->data[1]=0;
    self->data[2]=0;

    return (PyObject*) self;
}

static PyObject* vector3d_get_item(PyObject* self, Py_ssize_t i)
{
    return (PyObject*) PyFloat_FromDouble(((vector3d*)self)->data[i]);
}

static int vector3d_set_item(PyObject* self, Py_ssize_t i, PyObject *v)
{
    ((vector3d*) self)->data[i] = PyFloat_AsDouble(v);

    return 0;
}

static int vector3d_getbuffer(PyObject *exporter, Py_buffer *view, int flags)
{
    static Py_ssize_t shape[1] = {3};
    static Py_ssize_t stride[1] = {sizeof(double)};

    vector3d* self = (vector3d*) exporter;

    view->buf = self->data;
    view->len = shape[0]*stride[0];
    view->itemsize = stride[0];
    view->readonly = 0;
    view->format="d\0";
    view->ndim = 1;
    view->shape = shape;
    view->strides = stride;
    view->suboffsets = NULL;
    view->internal = NULL;

    view->obj=(PyObject*) self;
    Py_INCREF(self);
    return 0;
}

static PySequenceMethods seq_methods = {
    0,          /* length */
    0,          /* concat */
    0,          /* repeat */
    vector3d_get_item,      /* [i] */
    0,          /* slice */
    vector3d_set_item,      /* [i] = v */
    0,          /* del */
    0,          /* set slice */
    0,          /* del slice */
    0,          /* count */
};

static PyBufferProcs buf_procs = {
    0,
    0,
    0,
    0,
    vector3d_getbuffer,
    0,
};

static PyTypeObject vector3d_type = {
    PyObject_HEAD_INIT(NULL)
    0,                         /*ob_size*/
    "spam.vector3d",           /*tp_name*/
    sizeof(vector3d),          /*tp_basicsize*/
    0,                         /*tp_itemsize*/
    0,                 /*tp_dealloc*/
    0,                         /*tp_print*/
    0,                         /*tp_getattr*/
    0,                         /*tp_setattr*/
    0,                         /*tp_compare*/
    0,                         /*tp_repr*/
    0,                         /*tp_as_number*/
    &seq_methods,              /*tp_as_sequence*/
    0,                         /*tp_as_mapping*/
    0,                         /*tp_hash */
    0,                         /*tp_call*/
    0,                         /*tp_str*/
    0,                         /*tp_getattro*/
    0,                         /*tp_setattro*/
    &buf_procs,                /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_NEWBUFFER | Py_TPFLAGS_BASETYPE, /*tp_flags*/
    "3 dimensional vectors",   /* tp_doc */
    0,                     /* tp_traverse */
    0,                     /* tp_clear */
    0,                     /* tp_richcompare */
    0,                     /* tp_weaklistoffset */
    0,                     /* tp_iter */
    0,                     /* tp_iternext */
    0,                     /* tp_methods */
    0,                     /* tp_members */
    0,                         /* tp_getset */
    0,                         /* tp_base */
    0,                         /* tp_dict */
    0,                         /* tp_descr_get */
    0,                         /* tp_descr_set */
    0,                         /* tp_dictoffset */
    0,                 /* tp_init */
    0,                         /* tp_alloc */
    vector3d_new,              /* tp_new */
};

static PyMethodDef spam_methods[] = { {NULL} /* Sentinel */ };

#ifndef PyMODINIT_FUNC  /* declarations for DLL import/export */
#define PyMODINIT_FUNC void
#endif
PyMODINIT_FUNC initspam(void)
{
    PyObject* m;

    vector3d_type.tp_new = PyType_GenericNew;
    if (PyType_Ready(&vector3d_type) < 0)
        return;

    m = Py_InitModule3("spam", spam_methods,
                       "Example module that creates an extension type.");

    Py_INCREF(&vector3d_type);
    PyModule_AddObject(m, "vector3d", (PyObject *)&vector3d_type);
}