wrapper for initialize a detector

    Parameters:
    ----------
    net : str
        test network name
    prefix : str
        load model prefix
    epoch : int
        load model epoch
    data_shape : int
        resize image shape
    mean_pixels : tuple (float, float, float)
        mean pixel values (R, G, B)
    ctx : mx.ctx
        running context, mx.cpu() or mx.gpu(?)
    num_class : int
        number of classes
    nms_thresh : float
        non-maximum suppression threshold
    force_nms : bool
        force suppress different categories

def get_detector(net, prefix, epoch, data_shape, mean_pixels, ctx, num_class,
                 nms_thresh=0.5, force_nms=True, nms_topk=400):
    """
    wrapper for initialize a detector

    Parameters:
    ----------
    net : str
        test network name
    prefix : str
        load model prefix
    epoch : int
        load model epoch
    data_shape : int
        resize image shape
    mean_pixels : tuple (float, float, float)
        mean pixel values (R, G, B)
    ctx : mx.ctx
        running context, mx.cpu() or mx.gpu(?)
    num_class : int
        number of classes
    nms_thresh : float
        non-maximum suppression threshold
    force_nms : bool
        force suppress different categories
    """
    if net is not None:
        if isinstance(data_shape, tuple):
            data_shape = data_shape[0]
        net = get_symbol(net, data_shape, num_classes=num_class, nms_thresh=nms_thresh,
            force_nms=force_nms, nms_topk=nms_topk)
    detector = Detector(net, prefix, epoch, data_shape, mean_pixels, ctx=ctx)
    return detector