code: def _maybe_validate_prompt_template(self):
      assert (
          self.prompt_template is not None
      ), f"we need prompt_template to combine contexts and label {self.label_key}"
      # When providing things like newlines in the prompt template via the CLI, they are escaped. This line unescapes them.
      self.prompt_template = self.prompt_template.encode(
          "utf-8"
      ).decode("unicode_escape")
      self.prompt_template_keys = re.findall(
          r"{(.*?)}", self.prompt_template
      )
  
      label_placeholder = f"{{{self.label_key}}}"
      assert (
          self.prompt_template[-len(label_placeholder) :]
          == label_placeholder
      ), f"{label_placeholder} must be at the end of prompt_template."
  
      # Legacy checkpoints has self.truncation_fields = ['context'] and self.prompt_template_keys = ['input', 'output']
      if (
          self.prompt_template_keys[0] == "input"
          and self.truncation_fields[0] == "context"
      ):
          self.truncation_fields[0] = self.prompt_template_keys[0]
  
      assert set(self.truncation_fields).issubset(
          self.prompt_template_keys
      ), f"truncation_fields {self.truncation_fields} must in {self.prompt_template_keys}"
  
imports: import re
  from typing import List, Mapping, Optional
  import datasets
  import numpy
  import torch
  from datasets import load_dataset
  from nemo.collections.common.tokenizers.tokenizer_spec import TokenizerSpec
  from nemo.collections.nlp.data.language_modeling.megatron.dataset_utils import get_samples_mapping
  from nemo.collections.nlp.data.language_modeling.text_memmap_dataset import JSONLMemMapDataset
  from nemo.core.classes import Dataset
  from nemo.utils import logging
label_desc: Use image node_id 2 for calling the GPTSFTDataset obj's underlying member method code with example usage: obj._maybe_validate_prompt_template() without return types