code: def usable_id(cls, id):
          
          try:
              # id is maybe a hostname
              qry_id = cls.from_name(id)
              if not qry_id:
                  # id is maybe an ip
                  qry_id = cls.from_ip(id)
              if not qry_id:
                  qry_id = cls.from_vhost(id)
          except Exception:
              qry_id = None
  
          if not qry_id:
              msg = 'unknown identifier %s' % id
              cls.error(msg)
  
          return qry_id
docs: Retrieve id from input which can be hostname, vhost, id.