code: def get_params_for_field(self, field_name, sort_type=None):
          
          if not sort_type:
              if self.initial_sort == field_name:
                  sort_type = 'desc' if self.initial_sort_type == 'asc' else 'asc'
              else:
                  sort_type = 'asc'
          self.initial_params[self.sort_param_name] = self.sort_fields[field_name]
          self.initial_params[self.sort_type_param_name] = sort_type
          return '?%s' % self.initial_params.urlencode()
docs: If sort_type is None - inverse current sort for field, if no sorted - use asc