code: def generate_intervals(self) -> List[Tuple[int, int]]:
      intervals = []
      begin = 0
      end = 0
      for chunk in self._chunks:
          dim = chunk["dim"]
          num_blocks = dim // self._block_size
          end += num_blocks
          intervals.append((begin, end))
          begin += num_blocks
      return intervals
  
imports: import os
  from abc import ABC, abstractmethod
  from time import sleep
  from typing import Any, Dict, List, Optional, Tuple
  import numpy
  import torch
  from lightning.data.streaming.constants import _TORCH_DTYPES_MAPPING, _TORCH_GREATER_EQUAL_2_1_0
  from lightning.data.streaming.serializers import Serializer
label_desc: Use image node_id 4 for calling the TokensLoader obj's underlying member method code with example usage: obj.generate_intervals() and returns: intervals