Python: line replacement

How to replace line # 10 in a file, append a line at the end of the file ?

I found the solution and tested this successfully on local system but when i used fabric module to deploy in remote system, it modify the local hosts file and not remote. where i am wrong ? no errors reported.

[root@lb1oraoemc1p hp]# cat fabfile.py

#!/usr/bin/python

from fabric.api import cd,env,put,run

import fileinput,sys

env.hosts=['root@xyz'] # remote hostname xyz

f = open('/etc/default/xymon-client')

m = f.read().replace('XYMONSERVERS=""','XYMONSERVERS=aaa.xyz.com')

print m

f.close()

f = open('/etc/default/xymon-client','w')

f.write(m)

f.close()

with open("/etc/default/xymon-client","a") as myfile:

myfile.write("CLIENTHOSTNAME=bbb.xyz.com")



run('service xymon start')

I'd use ed . The script is

$ ed file_to_change
10s/.*/replacement text for line 10/
$a
text appended to file
more appended text
.
wq