code: def weights(self, mu):
          r
          return 1. / (self.link.deriv(mu)**2 * self.variance(mu))
docs: r"""
          Weights for IRLS steps
  
          Parameters
          ----------
          mu : array-like
              The transformed mean response variable in the exponential family
  
          Returns
          -------
          w : array
              The weights for the IRLS steps