通过“ElementTree"在 Python 中使用命名空间解析 XML [英] Parsing XML with namespace in Python via 'ElementTree'

问题描述

我想使用 Python 的 ElementTree 解析以下 XML:

I have the following XML which I want to parse using Python's ElementTree:

<rdf:RDF xml:base="http://dbpedia.org/ontology/"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns="http://dbpedia.org/ontology/">

    <owl:Class rdf:about="http://dbpedia.org/ontology/BasketballLeague">
        <rdfs:label xml:lang="en">basketball league</rdfs:label>
        <rdfs:comment xml:lang="en">
          a group of sports teams that compete against each other
          in Basketball
        </rdfs:comment>
    </owl:Class>

</rdf:RDF>

我想找到所有 owl:Class 标签，然后提取其中所有 rdfs:label 实例的值.我正在使用以下代码:

I want to find all owl:Class tags and then extract the value of all rdfs:label instances inside them. I am using the following code:

tree = ET.parse("filename")
root = tree.getroot()
root.findall('owl:Class')

由于命名空间的原因，我收到以下错误.

Because of the namespace, I am getting the following error.

SyntaxError: prefix 'owl' not found in prefix map

我尝试阅读 http://effbot.org/zone/element-namespaces.htm 上的文档但我仍然无法使其正常工作，因为上述 XML 具有多个嵌套命名空间.

I tried reading the document at http://effbot.org/zone/element-namespaces.htm but I am still not able to get this working since the above XML has multiple nested namespaces.

请告诉我如何更改代码以查找所有 owl:Class 标签.

Kindly let me know how to change the code to find all the owl:Class tags.

推荐答案

你需要给 .find(), findall() 和 iterfind() 方法显式命名空间字典:

You need to give the .find(), findall() and iterfind() methods an explicit namespace dictionary:

namespaces = {'owl': 'http://www.w3.org/2002/07/owl#'} # add more as needed

root.findall('owl:Class', namespaces)

前缀仅在您传入的namespaces 参数中查找.这意味着您可以使用任何您喜欢的命名空间前缀；API 拆分了 owl: 部分，在 namespaces 字典中查找相应的命名空间 URL，然后更改搜索以查找 XPath 表达式 {http://www.w3.org/2002/07/owl}Class 代替.当然，您也可以自己使用相同的语法:

Prefixes are only looked up in the namespaces parameter you pass in. This means you can use any namespace prefix you like; the API splits off the owl: part, looks up the corresponding namespace URL in the namespaces dictionary, then changes the search to look for the XPath expression {http://www.w3.org/2002/07/owl}Class instead. You can use the same syntax yourself too of course:

root.findall('{http://www.w3.org/2002/07/owl#}Class')

另见Parsing XML with Namespaces 部分.

如果您可以切换到lxml 库，情况会更好；该库支持相同的 ElementTree API，但在元素的 .nsmap 属性中为您收集命名空间，并且通常具有出色的命名空间支持.

If you can switch to the lxml library things are better; that library supports the same ElementTree API, but collects namespaces for you in .nsmap attribute on elements and generally has superior namespaces support.

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