code: def restore_walker(self, dumped_state):
          
  
          selector_string = dumped_state.get(u'selector')
          if selector_string is None:
              raise ArgumentError("Invalid stream walker state in restore_walker, missing 'selector' key", state=dumped_state)
  
          selector = DataStreamSelector.FromString(selector_string)
  
          walker = self.create_walker(selector)
          walker.restore(dumped_state)
          return walker
docs: Restore a stream walker that was previously serialized.
  
          Since stream walkers need to be tracked in an internal list for
          notification purposes, we need to be careful with how we restore
          them to make sure they remain part of the right list.
  
          Args:
              dumped_state (dict): The dumped state of a stream walker
                  from a previous call to StreamWalker.dump()
  
          Returns:
              StreamWalker: The correctly restored StreamWalker subclass.