code: def initialize_hooks(self):
          
          hooks = self._callbacks.get_hooks()
          self.hooked_sess = tfv1.train.MonitoredSession(
              session_creator=ReuseSessionCreator(self.sess), hooks=hooks)
docs: Create SessionRunHooks for all callbacks, and hook it onto `self.sess` to create `self.hooked_sess`.
  
          A new trainer may override this method to create multiple groups of hooks,
          which can be useful when the training is not done by a single `train_op`.