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 loadfile(cls, name):
      value = memcache.get(name, namespace="DatastoreFile")
      if value is None:
          file = cls.get_by_key_name(name)
          memcache.set(name, file.value, namespace="DatastoreFile")
      else:
          file = cls(value=value)
      file.data = BytesIO(file.value)
      return file
  
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 2 for calling the DatastoreFile obj's underlying member method code with example usage: obj.loadfile(cls, name) and returns: file