NLTK树的广度优先遍历

Question

我正在尝试在NLTK树上进行广度优先遍历。但是在当前节点上调用子树方法时，它不会给我子树，而是现有节点本身。

def traverseTree(tree):
    queue = [tree]
    visited = set(tree.label())

    while queue:
        node = queue.pop(0)

        for neighbor in node.subtrees():
            if neighbor.label() not in visited:
                queue.append(neighbor)
                visited.add(neighbor.label())

    return visited

任何人都可以告诉nltk树上的bfs怎么做？

def bfs(tree, children=iter, maxdepth=-1):
    queue = deque([(tree, 0)])

    while queue:
        node, depth = queue.popleft()
        yield node

        if depth != maxdepth:
            try:
                queue.extend((c, depth + 1) for c in children(node))
            except TypeError:
                pass

即使将其添加到我的代码中，我也无法调用此默认bfs实现。