def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def dec_r(self, ind):
        r, c = self.row_col(ind)
        r -= 1
        if r < 0:
            r = self.nr - 1
        if r == (self.nr - 1) and c == (self.nc - 1):
            r = self.nr - 2
        return self.indx(r, c)