python自动生成入库序列号

class Sequence(db.Model):
    __tablename__ = 'sys_sequence'
    __table_args__ = ({'comment': '序列维护表'})
    id = db.Column(db.Integer, autoincrement=True, primary_key=True)
    create_at = db.Column(db.DateTime, default=func.now(), comment='创建时间')
    update_at = db.Column(db.DateTime, default=func.now(), onupdate=func.now(), comment='更新时间')
    name = db.Column(db.String(255), comment='名称')
    cur_num = db.Column(db.Integer, comment='当前值')
    increase_by = db.Column(db.Integer, comment='步值')
    
    def merge(self):
	    db.session.merge(self)
	    db.session.commit()

    def save(self):
        db.session.add(self)
        db.session.flush()
        db.session.commit()

import datetime

def get_next_sequence(seq_name):
    from src.model.system.sequence import Sequence
    seq = Sequence.query.filter_by(name=seq_name).first()
    if seq is None:
        seq = Sequence()
        seq.name = seq_name
        seq.cur_num = 1
        seq.increase_by = 1
        seq.save()
        return 1
    seq.cur_num = seq.cur_num + seq.increase_by
    if __is_need_reset(seq.update_at):
        seq.cur_num = 1
    seq.update_at = datetime.datetime.now()
    seq.merge()
    return seq.cur_num


def __is_need_reset(check_date):
    cur_date = datetime.datetime.now()
    cur_year = cur_date.year
    check_year = check_date.year
    cur_day = cur_date.day
    check_day = check_date.day
    if cur_year == check_year and cur_day == check_day:
        return False
    else:
        return True

str(sequence.get_next_sequence('xxx')).zfill(3)