slicing the end of a string in a list

[Ben Cartwright]

John Salerno wrote:
> You can probably tell what I'm doing. Read a list of lines from a file,
> and then I want to slice off the '\n' character from each line. But
> after this code runs, the \n is still there. I thought it might have
> something to do with the fact that strings are immutable, but a test
> such as:
>
> switches[0][:-1]
>
> does slice off the \n character.

Actually, it creates a new string instance with the \n character
removed, then discards it.  The original switches[0] string hasn't
changed.

  >>> foo = 'Hello world!'
  >>> foo[:-1]
  'Hello world'
  >>> foo
  'Hello world!'

> So I guess the problem lies in the
> assignment or somewhere in there.

Yes.  You are repeated assigning a new string instance to "line", which
is then never referenced again.  If you want to update the switches
list, then instead of assigning to "line" inside the loop, you need:

  switches[i] = switches[i][:-1]

> Also, is this the best way to index the list?

No, since the line variable is unused.  This:

  i = 0
  for line in switches:
      line = switches[i][:-1]
      i += 1

Would be better written as:

  for i in range(len(switches)):
      switches[i] = switches[i][:-1]

For most looping scenarios in Python, you shouldn't have to manually
increment a counter variable.

--Ben

PS - actually, you can accomplish all of the above in a single line of
code:
  print [line[:-1] for line in open('C:\\switches.txt')]