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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 time_delays(self, kwargs_lens, kwargs_ps, kappa_ext=0):
 """ predicts the time delays of the image positions :param kwargs_lens: lens model parameters :param kwargs_ps: point source parameters :param kappa_ext: external convergence (optional) :return: time delays at image positions for the fixed cosmology """

        fermat_pot = self.lens_analysis.fermat_potential(kwargs_lens, kwargs_ps)
        time_delay = self.lensCosmo.time_delay_units(fermat_pot, kappa_ext)
        return time_delay