if __name__ == "__main__":
    class Node:
        def __init__(self, value):
            self._value = value
            self._children = []

        def __repr__(self):
            return 'Node({!r})'.format(self._value)

        def add_child(self, node):
            self._children.append(node)

        # 对象的内置iter方法，在迭代对象的时候将迭代请求转发，返回children的迭代器对象
        # iter函数和len函数一样，底层原理都是返回对象的底层方法，iter返回对象的__iter__()
        def __iter__(self):
            return iter(self._children)

    root = Node(0)
    child1 = Node(1)
    child2 = Node(2)
    root.add_child(child1)
    root.add_child(child2)

    for ch in root:
        print(ch)