code: def drop(self, filter_func=None, stash='active'):
          
          return self.move(stash, self.DROP, filter_func=filter_func)
docs: Drops states from a stash. This is an alias for move(), with defaults for the stashes.
  
          :param filter_func: Drop states that match this filter. Should be a function that takes
                              a state and returns True or False. (default: drop all states)
          :param stash:       Drop matching states from this stash. (default: 'active')
  
          :returns:           The simulation manager, for chaining.
          :rtype:             SimulationManager