## Replace the ... text below with a title and a summary of the problem.
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= I want to change an element in an array during a loop: =
{{{
 lines=open("/etc/fstab","r").readlines()
 for line in lines:
    if line.split()[1]=="/": 
       line="# "+line
}}}

Now that does not change the contents of the array (commenting out a particular line in the file).  I know you can easily make a loop counter, an d add i=i+1, but isn't there a better way?

== Answer==
Try using the enumerate builtin.
{{{
 lines=open("/etc/fstab","r").readlines()
 for index,line in enumerate(lines):
    if line.split()[1]=="/": 
       lines[index] ="# "+line
}}}
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