code: def list_all_elements(self):
          
          res = []
  
          # We are a host/service
          if self.operand in ['host', 'service']:
              return [self.sons[0]]
  
          for son in self.sons:
              res.extend(son.list_all_elements())
  
          # and returns a list of unique uuids
          return list(set(res))
docs: Get all host/service uuid in our node and below
  
          :return: list of hosts/services uuids
          :rtype: list