class_docstr: A file-like object that is backed by a BytesIO() object whose contents
  is loaded from a BlobProperty in the app engine datastore.
code: def readline(self):
      return self.data.readline()
  
imports: import time
  from google.appengine.api import memcache
  from google.appengine.ext import db
  from whoosh.compat import BytesIO
  from whoosh.index import TOC, FileIndex, _DEF_INDEX_NAME
  from whoosh.filedb.filestore import ReadOnlyError, Storage
  from whoosh.filedb.structfile import StructFile
label_desc: Use image node_id 8 for calling the DatastoreFile obj's underlying member method code with example usage: obj.readline() and returns: self