code: def _generate_file_set(self, var=None, start_date=None, end_date=None,
                             domain=None, intvl_in=None, dtype_in_vert=None,
                             dtype_in_time=None, intvl_out=None):
          
          try:
              return self.file_map[intvl_in]
          except KeyError:
              raise KeyError('File set does not exist for the specified'
                             ' intvl_in {0}'.format(intvl_in))
docs: Returns the file_set for the given interval in.