用lxml-extract元素值解析xml

Question

假设我们有如下结构的XML文件。

<?xml version="1.0" ?> 
<searchRetrieveResponse xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.loc.gov/zing/srw/ http://www.loc.gov/standards/sru/sru1-1archive/xml-files/srw-types.xsd" xmlns="http://www.loc.gov/zing/srw/">
  <records xmlns:ns1="http://www.loc.gov/zing/srw/">
    <record>
      <recordData>
        <record xmlns="">
          <datafield tag="000">
            <subfield code="a">123</subfield>
            <subfield code="b">456</subfield>
          </datafield>
          <datafield tag="001">
            <subfield code="a">789</subfield>
            <subfield code="b">987</subfield>
          </datafield>
        </record>
      </recordData>
    </record>
    <record>
      <recordData>
        <record xmlns="">
          <datafield tag="000">
            <subfield code="a">123</subfield>
            <subfield code="b">456</subfield>
          </datafield>
          <datafield tag="001">
            <subfield code="a">789</subfield>
            <subfield code="b">987</subfield>
          </datafield>
        </record>
      </recordData>
    </record>
  </records>
</searchRetrieveResponse>

我需要分析一下：

• “子字段”的内容（如上例中的123）和
• 属性值（例如000或001）

我想知道如何使用lxml和XPath来实现这一点。下面粘贴的是我的初始代码，我恳请有人解释我，如何解析出值。

import urllib, urllib2
from lxml import etree    

url = "https://dl.dropbox.com/u/540963/short_test.xml"
fp = urllib2.urlopen(url)
doc = etree.parse(fp)
fp.close()

ns = {'xsi':'http://www.loc.gov/zing/srw/'}

for record in doc.xpath('//xsi:record', namespaces=ns):
    print record.xpath("xsi:recordData/record/datafield[@tag='000']", namespaces=ns)

Answer 1

在XPath中我会更直接：直接寻找您想要的元素，在本例中是datafield。

>>> for df in doc.xpath('//datafield'):
        # Iterate over attributes of datafield
        for attrib_name in df.attrib:
                print '@' + attrib_name + '=' + df.attrib[attrib_name]

        # subfield is a child of datafield, and iterate
        subfields = df.getchildren()
        for subfield in subfields:
                print 'subfield=' + subfield.text

另外，lxml似乎允许忽略名称空间，可能是因为您的示例只使用一个名称空间？

Answer 2

请尝试以下工作代码：

import urllib2
from lxml import etree

url = "https://dl.dropbox.com/u/540963/short_test.xml"
fp = urllib2.urlopen(url)
doc = etree.parse(fp)
fp.close()

for record in doc.xpath('//datafield'):
    print record.xpath("./@tag")[0]
    for x in record.xpath("./subfield/text()"):
        print "\t", x

Answer 3

我只想和

for df in doc.xpath('//datafield'):
    print df.attrib
    for sf in df.getchildren():
        print sf.text

另外，您不需要urllib，可以使用HTTP直接解析XML

url = "http://dl.dropbox.com/u/540963/short_test.xml"  #doesn't work with https though
doc = etree.parse(url)