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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, **kw):
 r""" Returns the eccentricity computed from the mean apocenter and mean pericenter. .. math:: e = \frac{r_{\rm apo} - r_{\rm per}}{r_{\rm apo} + r_{\rm per}} Parameters **kw Any keyword arguments passed to ``apocenter()`` and ``pericenter()``. For example, ``approximate=True``. Returns ------- ecc : float The orbital eccentricity. """

        ra = self.apocenter(**kw)
        rp = self.pericenter(**kw)
        return (ra - rp) / (ra + rp)