code: def _conn_key(self, instance, db_key, db_name=None):
          ''' Return a key to use for the connection cache
          '''
          dsn, host, username, password, database, driver = self._get_access_info(instance, db_key, db_name)
          return '{}:{}:{}:{}:{}:{}'.format(dsn, host, username, password, database, driverf _conn_key(self, instance, db_key, db_name=None):
          ''' Return a key to use for the connection cache
          '''
          dsn, host, username, password, database, driver = self._get_access_info(instance, db_key, db_name)
          return '{}:{}:{}:{}:{}:{}'.format(dsn, host, username, password, database, driver)
docs: Return a key to use for the connection cache