code: def initialize(self, session_creator, session_init):
          
          assert isinstance(session_creator, tfv1.train.SessionCreator), session_creator
          assert isinstance(session_init, SessionInit), session_init
          session_init._setup_graph()
  
          logger.info("Creating the session ...")
  
          self.sess = session_creator.create_session()
          self.initialize_hooks()
  
          if self.is_chief:
              logger.info("Initializing the session ...")
              session_init._run_init(self.sess)
          else:
              if not isinstance(session_init, JustCurrentSession):
                  logger.warn("This is not a chief worker, 'session_init' was ignored!")
  
          self.sess.graph.finalize()
          logger.info("Graph Finalized.")
docs: Create the session and set `self.sess`.
          Call `self.initiailize_hooks()`
          Finalize the graph.
  
          It must be called after callbacks are setup.
  
          Args:
              session_creator (tf.train.SessionCreator):
              session_init (sessinit.SessionInit):