'Get the topological order of a CFG Node.
:param cfg_node: A CFGNode instance.
:return: An integer representing its order, or None if the CFGNode does not exist in the graph.'

def get_topological_order(self, cfg_node):

    if (not self._quasi_topological_order):
        self._quasi_topological_sort()
    return self._quasi_topological_order.get(cfg_node, None)
