code: def forward(self, x, attention_mask, head_mask=None):
      attention_feats = self.bert_selfattention(
          x, attention_mask, head_mask
      )
      features = self.fc(attention_feats[0])
      features = self.dropout(features)
      features = self.layernorm(features + x)
      if len(attention_feats) == 2:
          return (features, attention_feats[1])
      else:
          return (features,)
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle.nn import ReLU, Swish, GELU
  import math
  from ppdet.core.workspace import register
  from ..shape_spec import ShapeSpec
label_desc: Use image node_id 2 for calling the BertAttention obj's underlying member method code with example usage: obj.forward(x, attention_mask, head_mask) and returns: features,  attention_feats, features