code: def lock(self):
          
          
          self.password = None
          self.keyfile = None
          self.groups[:] = []
          self.entries[:] = []
          self._group_order[:] = []
          self._entry_order[:] = []
          self.root_group = v1Group()
          self._num_groups = 1
          self._num_entries = 0
          return True
docs: This method locks the database.