code: def forward(self, src_tokens, tgt_tokens, src_seq_len, first):
      prompt_state = self.generator(src_tokens, src_seq_len, first)
  
      decoder_outputs, prompt_state = self.prompt_decoder(
          tgt_tokens, prompt_state
      )
      return decoder_outputs
  
imports: import torch
  from torch import nn
  from torch.nn import functional
  from transformers.models.bart.configuration_bart import BartConfig
  from .modeling_bart import BartModel
  from ..utils.util import avg_token_embeddings, seq_to_mask, get_model_device
  from functools import partial
  from typing import Union
label_desc: Use image node_id 2 for calling the PromptBartModel obj's underlying member method code with example usage: obj.forward(src_tokens, tgt_tokens, src_seq_len, first) and returns: decoder_outputs