class_docstr: Reads `RecordIO` data format, and creates index file
  that enables random access.
  
  Example usage:
  ----------
  >>> creator = IndexCreator('data/test.rec','data/test.idx')
  >>> creator.create_index()
  >>> creator.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).
docstr: Returns the current position of read head.
          
docstr_tok: ["Returns","the","current","position","of","read","head","."]
code: def tell(self):
      """Returns the current position of read head."""
      pos = ctypes.c_size_t()
      check_call(
          _LIB.MXRecordIOReaderTell(self.handle, ctypes.byref(pos))
      )
      return pos.value
  
file_path: mxnet/tools/rec2idx.py
imports: from __future__ import print_function
  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 4 for calling the IndexCreator obj's underlying member method code with example usage: obj.tell() and returns: pos