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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 eccentricity(self):
 """ The eccentricity of the 2D Gaussian function that has the same second-order moments as the source. The eccentricity is the fraction of the distance along the semimajor axis at which the focus lies. .. math:: e = \\sqrt{1 - \\frac{b^2}{a^2}} where :math:`a` and :math:`b` are the lengths of the semimajor and semiminor axes, respectively. """


        l1, l2 = self.covariance_eigvals
        if l1 == 0:
            return 0.  # pragma: no cover
        return np.sqrt(1. - (l2 / l1))