def del_handler(self, handle):
        """
        Remove the handle registered for `handle`

        :raises KeyError:
            The handle wasn't registered.
        """
        _, _, _, respondent = self._handle_map.pop(handle)
        if respondent:
            self._handles_by_respondent[respondent].discard(handle)
Remove the handle registered for `handle`

        :raises KeyError:
            The handle wasn't registered.