If you want a command line script, is there a better way to handle the input argument than this?

data_to_rot13 = str(sys.argv[1:])

First, str(some_list) applied to a list will get you the repr of it:

>>> str(['a', 'b'])
"['a', 'b']"

The correct way is ' '.join.

Even so, I generally use optparse for such things, even if I'm not going to have options, unless it's a one-off script that I don't care about.

import optparse
parser = optparse.OptionParser(usage='%p "Hello, my name is Bob!"')
opts, args = parser.parse_args()
data_to_rot13 = ' '.join(args)

The advantage of this is that I can easily add options later.

Also, this live preview thing is neat. Is that a plugin?

Aye. It's called Live Comment Preview.

#! /usr/bin/python
# Usage:
# rot13.py 'Hello, my name is Bob!'
import sys
import codecs
data_to_rot13 = str(sys.argv[1:])
rot13ed_data = codecs.getencoder('rot13')(data_to_rot13)[0]
print rot13ed_data

Also, this live preview thing is neat. Is that a plugin?