code: def resort(self, columnName):
          csc = self.currentSortColumn
          newSortColumn = self.columns[columnName]
          if newSortColumn is None:
              raise Unsortable('column %r has no sort attribute' % (columnName,))
          if csc is newSortColumn:
              self.isAscending = not self.isAscending
          else:
              self.currentSortColumn = newSortColumn
              self.isAscending = True
          return self.isAscending