Fix var scope bug caught by Philippe.

Sure it worked, but for the wrong reason.
Intuition is that that x var should not been in scope,
was really just a renaming I forgot to do during refactor.

This makes me sad:
http://stackoverflow.com/a/4199355/446326

See also:
http://python-history.blogspot.com/2010/06/from-list-comprehensions-to-generator.html