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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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