code: def get_mnist_sym(output_op=None, num_hidden=400):
      
      net = mx.symbol.Variable('data')
      net = mx.symbol.FullyConnected(data=net, name='mnist_fc1', num_hidden=num_hidden)
      net = mx.symbol.Activation(data=net, name='mnist_relu1', act_type="relu")
      net = mx.symbol.FullyConnected(data=net, name='mnist_fc2', num_hidden=num_hidden)
      net = mx.symbol.Activation(data=net, name='mnist_relu2', act_type="relu")
      net = mx.symbol.FullyConnected(data=net, name='mnist_fc3', num_hidden=10)
      if output_op is None:
          net = mx.symbol.SoftmaxOutput(data=net, name='softmax')
      else:
          net = output_op(data=net, name='softmax')
      return net
docs: Get symbol of mnist