mysqldump -uroot -p123456 -A > backup.sql

def bak_db(self):
    #mysqldump -u%s -p%s -P%s -h%s -A > xx.sql
    #20180101.sql
    filename = str(datetime.date.today()) + '.sql'#备份今天的数据
    abs_file = os.path.join(self.path,filename)#变成绝对路径
    command = '''
    mysqldump -u{username} -p{password} -P{port} -h{ip} -A > {filename}
    '''.format(username=self.username,
               password=self.password,
               port = self.port,
               filename = abs_file,
               ip = self.ip)
    os.system(command) #这句命令在windows 和linux都可以执行
    print('done!数据库备份完成！')

db1 = BackDb('localhost','root','123456')