code: def add(self, host_value):
          
          host_obj = self._host_factory(host_value)
          if self._get_match(host_obj) is not None:
              return
          self._add_new(host_obj)
docs: Add the given value to the collection.
  
          :param host: an ip address or a hostname
          :raises InvalidHostError: raised when the given value
          is not a valid ip address nor a hostname