code: def __getitem__(self, idx):
      qn_tokens = self.qns["input_ids"][idx]
      ans_tokens = self.ans["input_ids"][idx]
      pad_tokens = [0] * (
          self.max_len - len(qn_tokens) - len(ans_tokens)
      )
      tokens = qn_tokens + ans_tokens + pad_tokens
      mask = (
          ([int(self.loss_on_prefix)] * len(qn_tokens))
          + ([1] * len(ans_tokens))
          + ([0] * len(pad_tokens))
      )
      tokens = th.tensor(tokens)
      mask = th.tensor(mask)
      return dict(input_ids=tokens, attention_mask=mask)
  
file_path: grade-school-math/grade_school_math/dataset.py
imports: import json
  import os
  import re
  import torch
label_desc: Use image node_id 3 for calling the GSMDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: dict