code: def get_external_instances(self, phase=None):
          
          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]
docs: 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