docs: def unhide_dataset(dataset_id,**kwargs):
      """
          Hide a particular piece of data so it can only be seen by its owner.
          Only an owner can hide (and unhide) data.
          Data with no owner cannot be hidden.
  
          The exceptions paramater lists the usernames of those with permission to view the data
          read, write and share indicate whether these users can read, edit and share this data.
      """
  
      user_id = kwargs.get('user_id')
      dataset_i = _get_dataset(dataset_id)
      #check that I can unhide the dataset
      if dataset_i.created_by != int(user_id):
          raise HydraError('Permission denied. '
                          'User %s is not the owner of dataset %s'
                          %(user_id, dataset_i.name))
  
      dataset_i.hidden = 'N'
      db.DBSession.flush()