code: def forward_once(self, x):
      output = self.cnn1(x)
      return output
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  import torchvision
  from torch.autograd import Variable
  from tensorboardX import SummaryWriter
  import pytest
label_desc: Use image node_id 2 for calling the SiameseNetwork obj's underlying member method code with example usage: obj.forward_once(x) and returns: output