code: def _unpack(self, record, key, expected):
          
          attrs = record.get(key)
          if attrs is None:
              return
          obj = unpack_from_dynamodb(
              attrs=attrs,
              expected=expected,
              model=self.model,
              engine=self.engine
          )
          object_loaded.send(self.engine, engine=self.engine, obj=obj)
          record[key] = obj
docs: Replaces the attr dict at the given key with an instance of a Model