docs: def _get_a(self, _type):
          """ Gets an instance implementing type <_type> """
          tmp = self._get_all(_type)
          ret = pick(tmp)
          if len(tmp) != 1:
              self.l.warn(("get_a: %s all implement %s; " +
                           "picking %s") % (tmp, _type, ret))
          return ret