code: def save(self, key, kw):
          
          if key not in self:
              obj = hdf5.LiteralAttrs()
          else:
              obj = self[key]
          vars(obj).update(kw)
          self[key] = obj
          self.flush()
docs: Update the object associated to `key` with the `kw` dictionary;
          works for LiteralAttrs objects and automatically flushes.