使用生成器时类型错误“类型”不可迭代错误

Question

我添加了一个生成器函数，以便能够迭代预定义的 BinaryTree 类，但是当我使用测试代码运行它时，我收到一个 TypeError 说 BinaryTree 类不可迭代，我不知道为什么。以下是提供的代码以及用于遍历树的生成器函数以及测试代码：

# Implement generator function to make class iterable

class BinaryTree:
    def __init__(self, content, leftSubtree=None, rightSubtree=None):
        self.content = content
        self.leftSubtree = leftSubtree
        self.rightSubtree = rightSubtree

    def __repr__(self):
        return str(self.content)

    def traverse(self):  # Generator implementation
        if self.rightSubtree:
            for leaf in self.rightSubtree:
                yield leaf
        yield self.content
        if self.leftSubtree:
            for leaf in self.leftSubtree:
                yield leaf

# Testing code

Node = BinaryTree

if __name__ == '__main__':
    s = Node(1) # Binary tree with 1 Node
    t = Node(10, s, None)   # Binary tree with 10 as content, 1 as left subtree
    tree = BinaryTree(20, None, t)  # Binary tree with 20 as content, no left subtree and t as right subtree

for x in (s, t, tree):
    print(x)

for node in tree:
    print(node)

这是之后打印出来的错误：

1
Traceback (most recent call last):
10
20
  File "...binaryTree_adt.py", line 34, in <module>
for node in tree:
TypeError: 'BinaryTree' object is not iterable

Process finished with exit code 1

我知道对于生成器，您不需要创建迭代器类，因为生成器将以类似的方式遍历项目。当我将“traverse”方法的名称更改为 iter 时，我没有收到任何错误，但是当名称更改时，我会这样做。

Answer 1

BinaryTree 本身不可迭代，不。只有BinaryTree().traverse()方法产生的结果是：

for node in tree.traverse():

但是，您还需要调整方法本身以使用子节点的.traverse() 方法：

def traverse(self):  # Generator implementation
    if self.rightSubtree:
        for leaf in self.rightSubtree.traverse():
            yield leaf
    yield self.content
    if self.leftSubtree:
        for leaf in self.leftSubtree.traverse():
            yield leaf

如果你想让一个实例 itself 可迭代，你需要实现一个__iter__ method，它要么返回一个迭代器（例如，生成器函数产生这个），要么返回__self__点您还需要提供next 或__next__ 方法，具体取决于您的Python 版本。

在这里，将 traverse 重命名为 __iter__ 就足够了：

class BinaryTree:
    def __init__(self, content, leftSubtree=None, rightSubtree=None):
        self.content = content
        self.leftSubtree = leftSubtree
        self.rightSubtree = rightSubtree

    def __repr__(self):
        return str(self.content)

    def __iter__(self):
        if self.rightSubtree:
            for leaf in self.rightSubtree:
                yield leaf
        yield self.content
        if self.leftSubtree:
            for leaf in self.leftSubtree:
                yield leaf

演示：

>>> class BinaryTree:
...     def __init__(self, content, leftSubtree=None, rightSubtree=None):
...         self.content = content
...         self.leftSubtree = leftSubtree
...         self.rightSubtree = rightSubtree
...     def __repr__(self):
...         return str(self.content)
...     def __iter__(self):
...         if self.rightSubtree:
...             for leaf in self.rightSubtree:
...                 yield leaf
...         yield self.content
...         if self.leftSubtree:
...             for leaf in self.leftSubtree:
...                 yield leaf
...
>>> Node = BinaryTree
>>> s = Node(1)
>>> t = Node(10, s, None)
>>> tree = BinaryTree(20, None, t)
>>> for x in (s, t, tree):
...     print(x)
...
1
10
20
>>> for node in tree:
...     print(node)
...
10
1
20