如何在Python和LXML中解析XML？

这是我的项目：我使用RRDTool绘制WeatherBug的天气数据。我需要一个简单而有效的方式从WeatherBug下载天气数据。我正在使用非常低效的bash脚本刮板，但转移到了BeautifulSoup。性能太慢（它运行在Raspberry Pi上），所以我需要使用LXML。如何在Python和LXML中解析XML？

我有什么至今：

from lxml import etree 
doc=etree.parse('weather.xml') 
print doc.xpath("//aws:weather/aws:ob/aws:temp")

但我得到一个错误信息。 Weather.xml是这样的：

<?xml version="1.0" encoding="UTF-8"?> 

<aws:weather xmlns:aws="http://www.aws.com/aws"> 
    <aws:api version="2.0"/> 
    <aws:WebURL>http://weather.weatherbug.com/PA/Tunkhannock-weather.html?ZCode=Z5546&amp;Units=0&amp;stat=TNKCN</aws:WebURL> 
    <aws:InputLocationURL>http://weather.weatherbug.com/PA/Tunkhannock-weather.html?ZCode=Z5546&amp;Units=0</aws:InputLocationURL> 
    <aws:ob> 
    <aws:ob-date> 
     <aws:year number="2013"/> 
     <aws:month number="1" text="January" abbrv="Jan"/> 
     <aws:day number="11" text="Friday" abbrv="Fri"/> 
     <aws:hour number="10" hour-24="22"/> 
     <aws:minute number="26"/> 
     <aws:second number="00"/> 
     <aws:am-pm abbrv="PM"/> 
     <aws:time-zone offset="-5" text="Eastern Standard Time (USA)" abbrv="EST"/> 
    </aws:ob-date> 
    <aws:requested-station-id/> 
    <aws:station-id>TNKCN</aws:station-id> 
    <aws:station>Tunkhannock HS</aws:station> 
    <aws:city-state zipcode="18657">Tunkhannock, PA</aws:city-state> 
    <aws:country>USA</aws:country> 
    <aws:latitude>41.5663871765137</aws:latitude> 
    <aws:longitude>-75.9794464111328</aws:longitude> 
    <aws:site-url>http://www.tasd.net/highschool/index.cfm</aws:site-url> 
    <aws:aux-temp units="&amp;deg;F">-100</aws:aux-temp> 
    <aws:aux-temp-rate units="&amp;deg;F">0</aws:aux-temp-rate> 
    <aws:current-condition icon="http://deskwx.weatherbug.com/images/Forecast/icons/cond013.gif">Cloudy</aws:current-condition> 
    <aws:dew-point units="&amp;deg;F">40</aws:dew-point> 
    <aws:elevation units="ft">886</aws:elevation> 
    <aws:feels-like units="&amp;deg;F">41</aws:feels-like> 
    <aws:gust-time> 
     <aws:year number="2013"/> 
     <aws:month number="1" text="January" abbrv="Jan"/> 
     <aws:day number="11" text="Friday" abbrv="Fri"/> 
     <aws:hour number="12" hour-24="12"/> 
     <aws:minute number="18"/> 
     <aws:second number="00"/> 
     <aws:am-pm abbrv="PM"/> 
     <aws:time-zone offset="-5" text="Eastern Standard Time (USA)" abbrv="EST"/> 
    </aws:gust-time> 
    <aws:gust-direction>NNW</aws:gust-direction> 
    <aws:gust-direction-degrees>323</aws:gust-direction-degrees> 
    <aws:gust-speed units="mph">17</aws:gust-speed> 
    <aws:humidity units="%">98</aws:humidity> 
    <aws:humidity-high units="%">100</aws:humidity-high> 
    <aws:humidity-low units="%">61</aws:humidity-low> 
    <aws:humidity-rate>3</aws:humidity-rate> 
    <aws:indoor-temp units="&amp;deg;F">77</aws:indoor-temp> 
    <aws:indoor-temp-rate units="&amp;deg;F">-1.1</aws:indoor-temp-rate> 
    <aws:light>0</aws:light> 
    <aws:light-rate>0</aws:light-rate> 
    <aws:moon-phase moon-phase-img="http://api.wxbug.net/images/moonphase/mphase01.gif">0</aws:moon-phase> 
    <aws:pressure units="&quot;">30.09</aws:pressure> 
    <aws:pressure-high units="&quot;">30.5</aws:pressure-high> 
    <aws:pressure-low units="&quot;">30.08</aws:pressure-low> 
    <aws:pressure-rate units="&quot;/h">-0.01</aws:pressure-rate> 
    <aws:rain-month units="&quot;">0.11</aws:rain-month> 
    <aws:rain-rate units="&quot;/h">0</aws:rain-rate> 
    <aws:rain-rate-max units="&quot;/h">0.12</aws:rain-rate-max> 
    <aws:rain-today units="&quot;">0.09</aws:rain-today> 
    <aws:rain-year units="&quot;">0.11</aws:rain-year> 
    <aws:temp units="&amp;deg;F">41</aws:temp> 
    <aws:temp-high units="&amp;deg;F">42</aws:temp-high> 
    <aws:temp-low units="&amp;deg;F">29</aws:temp-low> 
    <aws:temp-rate units="&amp;deg;F/h">-0.9</aws:temp-rate> 
    <aws:sunrise> 
     <aws:year number="2013"/> 
     <aws:month number="1" text="January" abbrv="Jan"/> 
     <aws:day number="11" text="Friday" abbrv="Fri"/> 
     <aws:hour number="7" hour-24="07"/> 
     <aws:minute number="29"/> 
     <aws:second number="53"/> 
     <aws:am-pm abbrv="AM"/> 
     <aws:time-zone offset="-5" text="Eastern Standard Time (USA)" abbrv="EST"/> 
    </aws:sunrise> 
    <aws:sunset> 
     <aws:year number="2013"/> 
     <aws:month number="1" text="January" abbrv="Jan"/> 
     <aws:day number="11" text="Friday" abbrv="Fri"/> 
     <aws:hour number="4" hour-24="16"/> 
     <aws:minute number="54"/> 
     <aws:second number="19"/> 
     <aws:am-pm abbrv="PM"/> 
     <aws:time-zone offset="-5" text="Eastern Standard Time (USA)" abbrv="EST"/> 
    </aws:sunset> 
    <aws:wet-bulb units="&amp;deg;F">40.802</aws:wet-bulb> 
    <aws:wind-speed units="mph">3</aws:wind-speed> 
    <aws:wind-speed-avg units="mph">1</aws:wind-speed-avg> 
    <aws:wind-direction>S</aws:wind-direction> 
    <aws:wind-direction-degrees>163</aws:wind-direction-degrees> 
    <aws:wind-direction-avg>SE</aws:wind-direction-avg> 
    </aws:ob> 
</aws:weather>

我用http://www.xpathtester.com/test来测试我的xpath，它在那里工作。但我得到的错误信息：

Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "lxml.etree.pyx", line 2043, in lxml.etree._ElementTree.xpath (src/lxml/lxml.etree.c:47570) 
    File "xpath.pxi", line 376, in lxml.etree.XPathDocumentEvaluator.__call__ (src/lxml/lxml.etree.c:118247) 
    File "xpath.pxi", line 239, in lxml.etree._XPathEvaluatorBase._handle_result (src/lxml/lxml.etree.c:116911) 
    File "xpath.pxi", line 224, in lxml.etree._XPathEvaluatorBase._raise_eval_error (src/lxml/lxml.etree.c:116728) 
lxml.etree.XPathEvalError: Undefined namespace prefix

这是所有非常新的我 - Python和XML和LXML。我想要的只是观察时间和温度。

难道我的问题与这个aws有什么关系：在所有内容前加前缀？那有什么意思？

任何帮助你可以提供非常感谢！

来源

2013-01-12 cisasteelersfan

这个问题与所有“与前面的所有aws：前缀”有关;它是一个必须定义的名称空间前缀。这是很容易实现，如：

print doc.xpath('//aws:weather/aws:ob/aws:temp', 
       namespaces={'aws': 'http://www.aws.com/aws'})[0].text

需要对命名空间前缀之间的映射值在http://lxml.de/xpathxslt.html被记录在案。

来源

2013-01-12 03:56:06 mmgp

尝试这样：

from lxml import etree 
ns = etree.FunctionNamespace("http://www.aws.com/aws") 
ns.prefix = "aws" 
doc=etree.parse('weather.xml') 
print doc.xpath("//aws:weather/aws:ob/aws:temp")[0].text

请参阅此链接：http://lxml.de/extensions.html

来源

2013-01-12 04:01:40

我喜欢这个解决办法，因为我不必每次我打电话的doc.xpath时间通过命名空间映射（）方法。 – jdhildeb

如何在Python和LXML中解析XML？

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