removing duplicates, or, converting Set() to string

[bearophileHUGS at lycos.com]

The write accepts strings only, so you may do:

out.write( repr(list(clean)) )

Notes:
- If you need the strings in a nice order, you may sort them before
saving them:
out.write( repr(sorted(clean)) )
- If you need them in the original order you need a stable method, you
can extract the relevant code from this large blob:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/438599

Bye,
bearophile