code: def add_user(self, ):
          
          i = self.user_tablev.currentIndex()
          item = i.internalPointer()
          if item:
              user = item.internal_data()
              if self._project:
                  self._project.users.add(user)
              else:
                  self._task.users.add(user)
              self.users.append(user)
              item.set_parent(None)
docs: Add a user and store it in the self.users
  
          :returns: None
          :rtype: None
          :raises: None