python从oracle读取数据写入到文件里

#coding:utf-8
#!/usr/bin/python
import cx_Oracle
import sys
import os
m=sys.argv[1]
sql="select a.mobile,b.city_name from (select mobile,city_id from  dw_cmmb_user_"+m+" where show_flag=1 group by mobile,city_id) a, (select * from dim_areacode where province_id=551) b where a.city_id=b.city_id group by a.mobile,b.city_name order by b.city_name"
db_conn=cx_Oracle.connect(admin/admin@hello')
cur=db_conn.cursor()
cur.execute(sql)
rows=cur.fetchall()
filename="/apps/aspbi/hello/anhui_"+m+".csv"
f=open(filename,'w')
for mobile,city_name in rows:
line=",".join([mobile,city_name])
f.write(line+'\n')
f.close()
db_conn.close()