def _find_export(self, func):
        # type: (Callable[[Tuple[Any, EndpointDescription]], bool]) -> Optional[Tuple[Any, EndpointDescription]]
        """
        Look for an export using the given lookup method

        The lookup method must accept a single parameter, which is a tuple
        containing a service instance and endpoint description.

        :param func: A function to look for the excepted export
        :return: The found tuple or None
        """
        with self._exported_instances_lock:
            for val in self._exported_services.values():
                if func(val):
                    return val

            return None
Look for an export using the given lookup method

        The lookup method must accept a single parameter, which is a tuple
        containing a service instance and endpoint description.

        :param func: A function to look for the excepted export
        :return: The found tuple or None