docs: def fmtd_sub_expr_str(self):
          """Get the entire sub expressions as a string with spaces."""
          result = u"{}({}".format(self.normalized_func,
                                   self._metric_name)
  
          if self._dimensions is not None:
              result += "{" + self.dimensions_str + "}"
  
          if self._period != _DEFAULT_PERIOD:
              result += ", {}".format(self._period)
  
          result += ")"
  
          result += " {} {}".format(self._operator,
                                    self._threshold)
  
          if self._periods != _DEFAULT_PERIODS:
              result += " times {}".format(self._periods)
  
          return result