code: def with_descriptor(self, descriptor):
          '''
          Returns any entities with the specified descriptor
          '''
          res = {}
          desc = "%s_descriptor" % descriptor
          for eid, ent in self.items():
              if desc in ent:
                  res[eid] = ent
          return ref with_descriptor(self, descriptor):
          '''
          Returns any entities with the specified descriptor
          '''
          res = {}
          desc = "%s_descriptor" % descriptor
          for eid, ent in self.items():
              if desc in ent:
                  res[eid] = ent
          return res
docs: Returns any entities with the specified descriptor