@property<EOL><INDENT>def identifier(self):<DEDENT>
if self.background_identifier is None:<EOL><INDENT>idsum = self._identifier_data()<EOL><DEDENT>else:<EOL><INDENT>idsum = hash_obj([self._identifier_data(),<EOL>self.background_identifier])<EOL><DEDENT>return idsum<EOL>
Return a unique identifier for the given data set