xml程序分析

请利用SAX编写程序解析Yahoo的XML格式的天气预报，获取当天和第二天的天气。
背景知识：handler是处理器。parser是解析器。parser负责读xml，handler负责处理parser读出的信息。
以下是别人的程序和自己的分析

#! -*- coding:utf-8 -*-from xml.parsers.expat import ParserCreateclass WeatherSaxHandler(object):    def __init__(self):        #定义了一个字典，装数据        self._data = {}        #定义_dayCount来控制输出今天和明天的天气。这个要结合后面代码体会，很有意思。        self._dayCount = 0    @property    def data(self):        return self._data    #分析xml，我们想要的信息都在start_element里。    def start_element(self, name, attrs):        #如果name为'yweather:location'，就把attrs['city']的值给self._data['city']        if name == 'yweather:location':            self._data['city'] = attrs['city']            self._data['country'] = attrs['country']        elif name == 'yweather:forecast':            if self._dayCount == 0:                self._data['today'] = {}                self._data['today']['text'] = attrs['text']                self._data['today']['low'] = int(attrs['low'])                self._data['today']['high'] = int(attrs['high'])                self._dayCount += 1            elif self._dayCount == 1:                self._data['tomorrow'] = {}                self._data['tomorrow']['text'] = attrs['text']                self._data['tomorrow']['low'] = int(attrs['low'])                self._data['tomorrow']['high'] = int(attrs['high'])                self._dayCount += 1    def end_element(self, name):        pass    def char_data(self, text):        passdef parse_weather(xml):    handler = WeatherSaxHandler()    parser = ParserCreate()    parser.StartElementHandler = handler.start_element    parser.EndElementHandler = handler.end_element    parser.CharacterDataHandler = handler.char_data    parser.Parse(xml)    #因为前面用了@property,所以这里用handler.data就可以。    return handler.datadata = r'''<?xml version="1.0" encoding="UTF-8" standalone="yes" ?><rss version="2.0" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">    <channel>        <title>Yahoo! Weather - Beijing, CN</title>        <lastBuildDate>Wed, 27 May 2015 11:00 am CST</lastBuildDate>        <yweather:location city="Beijing" region="" country="China"/>        <yweather:units temperature="C" distance="km" pressure="mb" speed="km/h"/>        <yweather:wind chill="28" direction="180" speed="14.48" />        <yweather:atmosphere humidity="53" visibility="2.61" pressure="1006.1" rising="0" />        <yweather:astronomy sunrise="4:51 am" sunset="7:32 pm"/>        <item>            <geo:lat>39.91</geo:lat>            <geo:long>116.39</geo:long>            <pubDate>Wed, 27 May 2015 11:00 am CST</pubDate>            <yweather:condition text="Haze" code="21" temp="28" date="Wed, 27 May 2015 11:00 am CST" />            <yweather:forecast day="Wed" date="27 May 2015" low="20" high="33" text="Partly Cloudy" code="30" />            <yweather:forecast day="Thu" date="28 May 2015" low="21" high="34" text="Sunny" code="32" />            <yweather:forecast day="Fri" date="29 May 2015" low="18" high="25" text="AM Showers" code="39" />            <yweather:forecast day="Sat" date="30 May 2015" low="18" high="32" text="Sunny" code="32" />            <yweather:forecast day="Sun" date="31 May 2015" low="20" high="37" text="Sunny" code="32" />        </item>    </channel></rss>'''weather = parse_weather(data)assert weather['city'] == 'Beijing', weather['city']assert weather['country'] == 'China', weather['country']assert weather['today']['text'] == 'Partly Cloudy', weather['today']['text']assert weather['today']['low'] == 20, weather['today']['low']assert weather['today']['high'] == 33, weather['today']['high']assert weather['tomorrow']['text'] == 'Sunny', weather['tomorrow']['text']assert weather['tomorrow']['low'] == 21, weather['tomorrow']['low']assert weather['tomorrow']['high'] == 34, weather['tomorrow']['high']print('Weather:', str(weather))