I didn't know about this one.  I'm looking at [the PEP](http://www.python.org/dev/peps/pep-0263/) and it doesn't have an example with UTF-8, but every time that it mentions UTF-8, it does have the hyphen which leads me to believe that this is more correct.

However, the code had been working under Python 2 previously which makes me start to doubt which one is correct.  Do you have a link to some more extensive than the PEP?