code: def get_active_namenode(self, max_staleness=None):
          
          if (max_staleness is None or
                  self._last_time_recorded_active is None or
                  self._last_time_recorded_active < time.time() - max_staleness):
              # Make a cheap request and rely on the reordering in self._record_last_active
              self.get_file_status('/')
          return self.hosts[0]
docs: Return the address of the currently active NameNode.
  
          :param max_staleness: This function caches the active NameNode. If this age of this cached
              result is less than ``max_staleness`` seconds, return it. Otherwise, or if this
              parameter is None, do a lookup.
          :type max_staleness: float
          :raises HdfsNoServerException: can't find an active NameNode