class_docstr: Loader for IndexedDataset
class_docstr_tok: ["Loader","for","IndexedDataset"]
code: def read_index(self, path):
      with open(index_file_path(path), "rb") as f:
          magic = f.read(8)
          assert magic == self._HDR_MAGIC, (
              "Index file doesn't match expected format. "
              "Make sure that --dataset-impl is configured properly."
          )
          version = f.read(8)
          assert struct.unpack("<Q", version) == (1,)
          code, self.element_size = struct.unpack("<QQ", f.read(16))
          self.dtype = dtypes[code]
          self._len, self.s = struct.unpack("<QQ", f.read(16))
          self.doc_count = struct.unpack("<Q", f.read(8))
          self.dim_offsets = read_longs(f, self._len + 1)
          self.data_offsets = read_longs(f, self._len + 1)
          self.sizes = read_longs(f, self.s)
          self.doc_idx = read_longs(f, self.doc_count)
  
imports: import os
  import shutil
  import struct
  from functools import lru_cache
  from itertools import accumulate
  import numpy
  import torch
label_desc: Use image node_id 2 for calling the IndexedDataset obj's underlying member method code with example usage: obj.read_index(path) without return types