code: def mongodb_ensure_index(database_name, collection_name, key):
      
  
      try:
          mongodb_client_url = getattr(settings, 'MONGODB_CLIENT',
                                   'mongodb://localhost:27017/')
          mc = MongoClient(mongodb_client_url,document_class=OrderedDict)
          dbs = mc[database_name]
          dbc = dbs[collection_name]
  
          dbc.ensure_index(key)
          # print "success"
          return key
  
      except:
          # error connecting to mongodb
          # print str(sys.exc_info())
          return str(sys.exc_info())
docs: Ensure Index