I pasted the changed line in my vim editor and it shows that the unprintable character is <U+FFEF>. By google search for `ffef character` I found http://stackoverflow.com/questions/7297888/ufeff-character-showing-up-in-files-how-to-remove-them and
http://www.ueber.net/who/mjl/projects/bomstrip/ 

And the line `# -*- coding: utf-8 -*-` is not a comment it is a method of specifying the character encoding of the python files.
http://www.python.org/dev/peps/pep-0263/