class_docstr: Hugging Face LlamaForSequenceClassification.
  
  Llama is a multi-layer decoder-only Transformer. As such, the encoder
  is simply an identity layer. The decoder is initialized with pretrained
  weights from Hugging Face. Read more about this model here
  <https://huggingface.co/docs/transformers/main/model_doc/llama>.
  
  parlai em -m parlai.agents.hugging_face.llama:ParlaiLlamaClassifierAgent --classes __notok__ __ok__
docstr: Add the start and end token to the text.
docstr_tok: ["Add","the","start","and","end","token","to","the","text","."]
code: def _set_text_vec(self, *args, **kwargs):
      """
      Add the start and end token to the text.
      """
      obs = super()._set_text_vec(*args, **kwargs)
  
      if "text_vec" in obs and "added_start_end" not in obs:
          obs.force_set(
              "text_vec",
              self._add_start_end_tokens(
                  obs["text_vec"],
                  add_start=(not self.dict.add_special_tokens),
                  add_end=False,
              ),
          )
          obs["added_start_end"] = True
  
      # check truncation after adding start end tokens
      if obs.get("text_vec") is not None:
          truncated_vec = self._check_truncate(
              obs["text_vec"], self.text_truncate, truncate_left=True
          )
          obs.force_set("text_vec", torch.LongTensor(truncated_vec))
  
      return obs
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  import torch
  from parlai.agents.hugging_face.dict import LlamaDictionaryAgent, _init_llama_path
  from parlai.core.torch_generator_agent import TorchGeneratorAgent, TorchGeneratorModel
  from parlai.core.torch_classifier_agent import TorchClassifierAgent
  from parlai.utils.torch import IdentityLayer, padded_tensor
  from parlai.agents.transformer.transformer import _check_positional_embeddings
  import parlai.utils.logging
label_desc: Use image node_id 4 for calling the ParlaiLlamaClassifierAgent obj's underlying member method code with example usage: obj._set_text_vec() and returns: obs