RFE: better error messages from ntpsweep for non-existent host

$ python3 ./ntpsweep/ntpsweep -l does.not.exist.invalid -p
Host                             st offset(s) version     system       processor
--------------------------------+--+---------+-----------+------------+---------
ntpq: standard-mode lookup of does.not.exist.invalid failed, nodename nor servname provided, or not known
ntpq: ndp lookup failed, nodename nor servname provided, or not known
***No host open, use `host' command

And the first 2 lines of error messages are prefixed with "ntpq". The host open error message references the "host" command, which is specific to ntpq.

Should session.openhost() throw an exception that ntpsweep could catch, so that it doesn't call readvar() on a dead session?