Slicing every element of a list

Recently I tried to slice every element of a list of strings. First I tried:

f = open("export.xls", "r")
lines = f.readlines()

for line in lines:
    line = line[1:-5]
    line = line.split('\"\t\"')

This went without returning any errors, but nothing was sliced or
split. Next I tried:

for i in range(len(lines)):
    lines[i] = lines[i][1:-5]
    lines[i] = lines[i].split('\"\t\"')

This of course worked, but why didn't the first one work. Further why
didn't the first one return an error?
Received on Thu Sep 29 16:54:43 2005