Calculates the distortion value of the current clusters

def _calc_distortion(self):
        """Calculates the distortion value of the current clusters
        """
        m = self._X.shape[0]
        self.distortion = 1/m * sum(
            linalg.norm(self._X[i, :] - self.centroids[self.clusters[i]])**2 for i in range(m)
        )
        return self.distortion