code: def forward(self, src, mask):
      x = self.embedding(src)
      x = self.posencoding(x)
      for i in range(self.n_layers):
          x = self.layers[i](x, mask)
      return self.layernorm(x)
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  import math
  import copy
label_desc: Use image node_id 2 for calling the TransformerEncoder obj's underlying member method code with example usage: obj.forward(src, mask) and returns: self