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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 metric(self):
 """ Compute a matrix of Hilbert-Schmidt inner products for the basis operators, update self._metric, and return the value. :return: The matrix of inner products. :rtype: numpy.matrix """

        if self._metric is None:
            _log.debug("Computing and caching operator basis metric")
            self._metric = np.matrix([[(j.dag() * k).tr() for k in self.ops] for j in self.ops])
        return self._metric