How to use the numdifftools.extrapolation.Richardson function in numdifftools

def set_richardson_rule(self, step_ratio, num_terms=2):
        order = self._method_order
        step = self._richardson_step()
        self.richardson = Richardson(step_ratio=step_ratio,
                                     step=step, order=order,
                                     num_terms=num_terms)

def _set_richardson_rule(self, step_ratio, num_terms=2):
        self.richardson = Richardson(step_ratio=step_ratio, step=1, order=1,
                                     num_terms=num_terms)

def __init__(self, fun, step=None, method='above', order=4, full_output=False, **options):
        self.fun = fun
        self.method = method
        self.order = order
        self.full_output = full_output
        self.step = step, options

        self.richardson = Richardson(step_ratio=1.6, step=1, order=1, num_terms=2)