<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def notation(self):
 """ A ``dict`` of notation data in this signature, if any. Otherwise, an empty ``dict``. """

        return dict((nd.name, nd.value) for nd in self._signature.subpackets['NotationData'])