def _validate_sort_field(self, sort_by):
if (<EOL>sort_by not in self.RESPONSE_FIELD_MAP<EOL>or not self.RESPONSE_FIELD_MAP[sort_by].is_sort<EOL>):<EOL><INDENT>raise InvalidSortFieldException(<EOL>'<STR_LIT>'.format(sort_by)<EOL>)<EOL><DEDENT>
:param sort_by: string
:raises: pybomb.exceptions.InvalidSortFieldException