class_docstr: An implementation of :class:`whoosh.store.Storage` that stores files in
  the app engine datastore as blob properties.
code: def list(self):
      query = DatastoreFile.all()
      keys = []
      for file in query:
          keys.append(file.key().id_or_name())
      return keys
  
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 3 for calling the DatastoreStorage obj's underlying member method code with example usage: obj.list() and returns: keys