Code golf challenge: XKCD 936 passwords

[Roy Smith]

In article <mailman.885.1381284610.18130.python-list at python.org>,
 Chris Angelico <rosuav at gmail.com> wrote:

> On Wed, Oct 9, 2013 at 12:38 PM, Roy Smith <roy at panix.com> wrote:
> > If you're willing to accept a sub-optimal random number generator:
> >
> > # Python-2, sorry
> > import os
> > print list(set(open('/usr/share/dict/words')))[os.getpid():][:4]
> 
> So that steps by your pid? That's going to drastically reduce the
> entropy in the result,

Well, I did say it was a sub-optimal random number generator :-)

I've been experimenting with os.urandom() as an entropy source, but 
can't get the (source code) character count down far enough.