def get_external_instances(self, phase=None):
        """Get a list of external instances (in a specific phase)

        If phase is None, return all external instances whtever the phase

        :param phase: phase to filter (never used)
        :type phase:
        :return: external instances list
        :rtype: list
        """
        if phase is None:
            return [instance for instance in self.instances if instance.is_external]

        return [instance for instance in self.instances
                if instance.is_external and phase in instance.phases and
                instance not in self.to_restart]
Get a list of external instances (in a specific phase)

        If phase is None, return all external instances whtever the phase

        :param phase: phase to filter (never used)
        :type phase:
        :return: external instances list
        :rtype: list