postorder.py

    def postorder_traversal(self, node=None):
        """Yields every node in the tree in post-order"""
        root = node or self.root
        stack = deque([(root, 'yield'), (root, 'children')])
        while len(stack) > 0:
            (node, action) = stack.pop()
            if action == 'yield':
                yield node
            elif action == 'children':
                for i in reversed(range(len(node.children))):
                    stack.append((node.children[i], 'yield'))
                    stack.append((node.children[i], 'children'))