'detect all images in iterator
Parameters:
det_iter : DetIter
iterator for all testing images
show_timer : Boolean
whether to print out detection exec time
Returns:
list of detection results'

def detect(self, det_iter, show_timer=False):

    num_images = det_iter._size
    if (not isinstance(det_iter, mx.io.PrefetchingIter)):
        det_iter = mx.io.PrefetchingIter(det_iter)
    start = timer()
    detections = self.mod.predict(det_iter).asnumpy()
    time_elapsed = (timer() - start)
    if show_timer:
        print('Detection    time    for    {}    images:    {:.4f}    sec'.format(num_images, time_elapsed))
    result = []
    for i in range(detections.shape[0]):
        det = detections[i, :, :]
        res = det[np.where((det[:, 0] >= 0))[0]]
        result.append(res)
    return result
