XPath:选择值为空的标签 [英] XPath: select tag with empty value

问题描述

如何在XPath 1.0中查找所有col name="POW"为空的行?

How I can find in XPath 1.0 all rows with empty col name="POW"?

<row>
<col name="WOJ">02</col>
<col name="POW"/>
<col name="GMI"/>
<col name="RODZ"/>
<col name="NAZWA">DOLNOŚLĄSKIE</col>
<col name="NAZDOD">województwo</col>
<col name="STAN_NA">2011-01-01</col>
</row>

我尝试了许多解决方案.在Firefox扩展中选择XPath Checker的次数很少，但是lxml.xpath()表示表达式无效或仅不返回任何行.

I tried many solutions. Few times in Firefox extension XPath Checker selection was ok, but lxml.xpath() says that expression is invalid or just returns no rows.

我的Python代码:

My Python code:

from lxml import html
f = open('TERC.xml', 'r')
page = html.fromstring(f.read())
for r in page.xpath("//row[col[@name = 'POW' and not(text())]]"):
    print r.text_content()
    print "-------------------------"

推荐答案

如何在XPath 1.0中查找所有col name="POW"为空的行?

空"有许多可能的定义，并且每个定义都有一个不同的XPath表达式来选择空"元素.

There are many possible definitions of "empty" and for each one of them there is a different XPath expression selecting "empty" elements.

对于空元素的合理定义是:没有子元素且没有文本节点子元素的元素，或者具有单个文本节点子元素的元素，其字符串值仅包含空格字符.

A reasonable definition for an empty element is: an element that has no children elements and no text-node children, or an element that has a single text-node child, whose string value contains only whitespace characters.

此XPath表达式:

//row[col[@name = 'POW']
                    [not(*)]
                       [not(normalize-space())]
      ]

选择XML文档中的所有row元素，这些元素具有col子元素，该元素具有属性name的字符串值"POW"并且没有子元素-元素并且其字符串值完全由以下元素组成:空格字符，或者是空字符串.

selects all row elements in the XML document, that have a col child, that has an attribute name with string value "POW" and that has no children - elements and whose string value consists either entirely of whitespace characters, or is the empty string.

如果空"表示您理解为根本没有子代" ，这意味着没有子代元素，没有子代PI节点，也没有子代注释节点，请使用:

In case by "empty" you understand "having no children at all", which means no children elements and no children PI nodes and no children comment nodes, then use:

//row[col[@name = 'POW']
                    [not(node())]
      ]

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