code: def register_deleted(self, entity_class, entity):
          
          EntityState.manage(entity, self)
          EntityState.get_state(entity).status = ENTITY_STATUS.DELETED
          self.__entity_set_map[entity_class].add(entity)
docs: Registers the given entity for the given class as DELETED.
  
          :raises ValueError: If the given entity already holds state that was
            created by another Unit Of Work.