docs: def model_fn(model_dir):
      """
      Load the gluon model. Called once when hosting service starts.
  
      :param: model_dir The directory where model files are stored.
      :return: a model (in this case a Gluon network)
      """
      symbol = mx.sym.load('%s/model.json' % model_dir)
      outputs = mx.symbol.softmax(data=symbol, name='softmax_label')
      inputs = mx.sym.var('data')
      param_dict = gluon.ParameterDict('model_')
      net = gluon.SymbolBlock(outputs, inputs, param_dict)
      net.load_params('%s/model.params' % model_dir, ctx=mx.cpu())
      return net