code: def postinit(self, lower=None, upper=None, step=None):
          
          self.lower = lower
          self.upper = upper
          self.step = step
docs: Do some setup after initialisation.
  
          :param lower: The lower index in the slice.
          :value lower: NodeNG or None
  
          :param upper: The upper index in the slice.
          :value upper: NodeNG or None
  
          :param step: The step to take between index.
          :param step: NodeNG or None