code: def unpersist(self, blocking=False):
          
          if self._jbroadcast is None:
              raise Exception("Broadcast can only be unpersisted in driver")
          self._jbroadcast.unpersist(blocking)
docs: Delete cached copies of this broadcast on the executors. If the
          broadcast is used after this is called, it will need to be
          re-sent to each executor.
  
          :param blocking: Whether to block until unpersisting has completed