code: def parse(self, commands):
          
  
          # Get rid of dummy objects that represented deleted objects in
          # the last parsing round.
          to_delete = []
          for id_, val in self._objects.items():
              if val == JUST_DELETED:
                  to_delete.append(id_)
          for id_ in to_delete:
              self._objects.pop(id_)
  
          for command in commands:
              self._parse(command)
docs: Parse a list of commands.