#boxes = [(1,2,3,4),(2,1,3,4),(4,3,2,1)] # a list of tuples ?
boxes = np.array([[[1,2,3,4],[2,1,3,4],[4,3,2,1]]],np.int32) # a (2d) numpy array ?
conf = np.array([.6, .5, .2], np.float32)
indices = cv2.dnn.NMSBoxes(boxes, conf, .1, .1)
# expected: [0,2], but we get:

SystemError: <built-in function NMSBoxes> returned NULL without setting an error

static PyObject* pyopencv_cv_dnn_NMSBoxes(PyObject* , PyObject* args, PyObject* kw)
{
    using namespace cv::dnn;

    PyObject* pyobj_bboxes = NULL;
    vector_Rect bboxes;
    PyObject* pyobj_scores = NULL;
    vector_float scores;
    float score_threshold=0.f;
    float nms_threshold=0.f;
    vector_int indices;
    float eta=1.f;
    int top_k=0;

    const char* keywords[] = { "bboxes", "scores", "score_threshold", "nms_threshold", "eta", "top_k", NULL };
    if( PyArg_ParseTupleAndKeywords(args, kw, "OOff|fi:NMSBoxes", (char**)keywords, &pyobj_bboxes, &pyobj_scores, &score_threshold, &nms_threshold, &eta, &top_k) &&
        pyopencv_to(pyobj_bboxes, bboxes, ArgInfo("bboxes", 0)) &&
        pyopencv_to(pyobj_scores, scores, ArgInfo("scores", 0)) )
    {
        ERRWRAP2(cv::dnn::NMSBoxes(bboxes, scores, score_threshold, nms_threshold, indices, eta, top_k));
        return pyopencv_from(indices);
    }

    return NULL;
}