class_docstr: An implementation of :class:`whoosh.store.Storage` that stores files in
  the app engine datastore as blob properties.
code: def rename_file(self, name, newname, safe=False):
      file = DatastoreFile.get_by_key_name(name)
      newfile = DatastoreFile(key_name=newname)
      newfile.value = file.value
      newfile.mtime = file.mtime
      newfile.put()
      file.delete()
  
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 10 for calling the DatastoreStorage obj's underlying member method code with example usage: obj.rename_file(name, newname, safe) without return types