code: def forward(self, x):
      sn_conv1 = self._sn_conv1.forward(x)
      pad_2d = self._pad2d.forward(sn_conv1)
      sn_conv2 = self._sn_conv2.forward(pad_2d)
      sn_conv3 = self._sn_conv3.forward(sn_conv2)
      return sn_conv3
  
imports: import paddle
  import paddle.nn
  from arch.spectral_norm import spectral_norm
label_desc: Use image node_id 2 for calling the MiddleNet obj's underlying member method code with example usage: obj.forward(x) and returns: sn_conv3