<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def map_get(self, key, mapkey):
 """ Retrieve a value from a map. :param str key: The document ID :param str mapkey: Key within the map to retrieve :return: :class:`~.ValueResult` :raise: :exc:`IndexError` if the mapkey does not exist :raise: :cb_exc:`NotFoundError` if the document does not exist. .. seealso:: :meth:`map_add` for an example """

        op = SD.get(mapkey)
        sdres = self.lookup_in(key, op)
        return self._wrap_dsop(sdres, True)