class_docstr: An implementation of :class:`whoosh.store.Storage` that stores files in
  the app engine datastore as blob properties.
code: def total_size(self):
      return sum(self.file_length(f) for f in self.list())
  
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 5 for calling the DatastoreStorage obj's underlying member method code with example usage: obj.total_size() and returns: sum