title: Validate a hostname string
body: <p>Following up to <a href="https://stackoverflow.com/questions/106179/regular-expression-to-match-hostname-or-ip-address">Regular expression to match hostname or IP Address?</a>
  and using <a href="http://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names" rel="noreferrer">Restrictions on valid host names</a> as a reference, what is the most readable, concise way to match/validate a hostname/fqdn (fully qualified domain name) in Python?  I've answered with my attempt below, improvements welcome.</p>