from xml.etree.ElementTree import iterparse
from urllib.request import urlopen


# 在尤其关注节省内存时，牺牲运行速度，使用增量生成的方式读取XML文档
def parse_and_remove(filename, path):
    # 将节点路径划分
    path_parts = path.split('/')
    # 通过迭代的方式解析XML文件
    doc = iterparse(filename, events=('start', 'end'))
    # 跳过根节点
    next(doc)

    # 设置存储栈
    tag_stack = []
    elem_stack = []

    for event, elem in doc:
        # iterparse会输出event和elem元组，表示状态和元素
        if event == 'start':
            # 如果检测状态是start就入栈
            tag_stack.append(elem.tag)
            elem_stack.append(elem)
        elif event == 'end':
            # 如果检测状态是end就出栈
            # print(tag_stack, path_parts)

            # 如果路径和需要寻找的标签相同，就生成并从栈中抹除
            if tag_stack == path_parts:
                yield elem
                elem_stack[-2].remove(elem)
            try:
                tag_stack.pop()
                elem_stack.pop()
            except IndexError:
                pass



if __name__ == '__main__':
    u = urlopen('http://planet.python.org/rss20.xml')
    data = parse_and_remove(u, 'channel/item/title')
    # print(data)
    for d in data:
        print(d.text)