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