Opening and appending to file in Python3

[jakey]

I am really enjoying myself learning Python3. But now i seem to have hit a brick wall and cannot find a way around it.
I have been practicing the little i know of python3 with a simple little script called "practice.py" as follows:

#!/usr/bin/env python3
#
practice = ["Billy", "John", "Peter", "Simon", "Kevin"]
print(*practice, sep='\n')

Which returned the following:

Billy
John
Peter
Simon
Kevin

Flushed with success i decided to add another name to the list using: