code: def to_line(self):
          
          if self.valid:
              return '%s %s %s\n' % (','.join(self.hostnames), self.key.get_name(),
                     self.key.get_base64())
          return None
docs: Returns a string in OpenSSH known_hosts file format, or None if
          the object is not in a valid state.  A trailing newline is
          included.