def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def inc_c(self, ind):
        r, c = self.row_col(ind)
        c += 1
        if c == self.nc:
            c = 0
        if r == (self.nr - 1) and c == (self.nc - 1):
            c = 0
        return self.indx(r, c)