Returns the width of each node in the graph. #TODO

def node_width(self):
        """
        Returns the width of each node in the graph. #TODO
        
        """
        nodes = self.postorder()
        node_width = {}
        for node in nodes:
            sum_width = 0
            for child in self[node].nodes():
                sum_width += node_width[child]
            node_width[node] = (sum_width or 1)
        return node_width