class_docstr: Reads `RecordIO` data format, and creates index file
  that enables random access.
  
  Example usage:
  ----------
  >> creator = IndexCreator('data/test.rec','data/test.idx')
  >> record.create_index()
  >> record.close()
  >> !ls data/
  test.rec  test.idx
  
  Parameters
  ----------
  uri : str
      Path to the record file.
  idx_path : str
      Path to the index file, that will be created/overwritten.
  key_type : type
      Data type for keys (optional, default = int).
code: def __init__(self, uri, idx_path, key_type=int):
      self.key_type = key_type
      self.fidx = None
      self.idx_path = idx_path
      super(IndexCreator, self).__init__(uri, "r")
  
file_path: DALI/tools/rec2idx.py
imports: import os
  import time
  import ctypes
  from mxnet.base import _LIB
  from mxnet.base import check_call
  import mxnet
  import argparse
label_desc: Use image node_id 1 to create a new IndexCreator object from inherited base classes: mx.recordio with example: obj = IndexCreator(uri, idx_path, key_type)