code: def set_load_from(self, load_from):
          
          assert load_from is None or isinstance(load_from, Cache), \
              "load_from needs to be None or a Cache object."
          assert load_from is None or load_from.cl_size <= self.cl_size, \
              "cl_size may only increase towards main memory."
          self.load_from = load_from
          self.backend.load_from = load_from.backend
docs: Update load_from in Cache and backend.