def postinit(self, lower=None, upper=None, step=None):
self.lower = lower<EOL>self.upper = upper<EOL>self.step = step<EOL>
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