从 ElementTree findall 返回的空列表 [英] Empty list returned from ElementTree findall

问题描述

我是 xml 解析和 Python 的新手，所以请耐心等待.我正在使用 lxml 来解析 wiki 转储，但我只想要每个页面、它的标题和文本.

现在我有这个:

from xml.etree import ElementTree as etree定义解析器(文件名):文档 = etree.parse(file_name)titles = document.findall('.//title')印刷标题

目前 titles 没有返回任何内容.我看过像这样的以前的答案:(Python 3.3 文档 更好.

另见http://effbot.org/zone/element-namespaces.htm 以及这个带有答案的问题:通过ElementTree"在 Python 中解析带有命名空间的 XML.

<小时>

的问题iterparse() 是因为这个函数提供了 (event, element) 元组(不仅仅是元素).为了获取标签名称，更改

 for e 在 etree.iterparse(file_name):打印电子标签

为此:

 for e 在 etree.iterparse(file_name):打印 e[1].tag

I'm new to xml parsing and Python so bear with me. I'm using lxml to parse a wiki dump, but I just want for each page, its title and text.

For now I've got this:

from xml.etree import ElementTree as etree

def parser(file_name):
    document = etree.parse(file_name)
    titles = document.findall('.//title')
    print titles

At the moment titles isn't returning anything. I've looked at previous answers like this one: ElementTree findall() returning empty list and the lxml documentation, but most things seemed to be tailored towards parsing HTML.

This is a section of my XML:

<mediawiki xmlns="http://www.mediawiki.org/xml/export-0.7/"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.mediawiki.org/xml/export-0.7/ http://www.mediawiki.org/xml/export-0.7.xsd" version="0.7" xml:lang="en">
  <siteinfo>
  <sitename>Wikipedia</sitename>
<base>http://en.wikipedia.org/wiki/Main_Page</base>
<generator>MediaWiki 1.20wmf9</generator>
<case>first-letter</case>
<namespaces>
  <namespace key="-2" case="first-letter">Media</namespace>
  <namespace key="-1" case="first-letter">Special</namespace>
  <namespace key="0" case="first-letter" />
  <namespace key="1" case="first-letter">Talk</namespace>
  <namespace key="2" case="first-letter">User</namespace>
  <namespace key="3" case="first-letter">User talk</namespace>
  <namespace key="4" case="first-letter">Wikipedia</namespace>
  <namespace key="5" case="first-letter">Wikipedia talk</namespace>
  <namespace key="6" case="first-letter">File</namespace>
  <namespace key="7" case="first-letter">File talk</namespace>
  <namespace key="8" case="first-letter">MediaWiki</namespace>
  <namespace key="9" case="first-letter">MediaWiki talk</namespace>
  <namespace key="10" case="first-letter">Template</namespace>
  <namespace key="11" case="first-letter">Template talk</namespace>
  <namespace key="12" case="first-letter">Help</namespace>
  <namespace key="13" case="first-letter">Help talk</namespace>
  <namespace key="14" case="first-letter">Category</namespace>
  <namespace key="15" case="first-letter">Category talk</namespace>
  <namespace key="100" case="first-letter">Portal</namespace>
  <namespace key="101" case="first-letter">Portal talk</namespace>
  <namespace key="108" case="first-letter">Book</namespace>
  <namespace key="109" case="first-letter">Book talk</namespace>
</namespaces>
  </siteinfo>
  <page>
    <title>Aratrum</title>
    <ns>0</ns>
    <id>65741</id>
    <revision>
  <id>349931990</id>
  <parentid>225434394</parentid>
  <timestamp>2010-03-15T02:55:02Z</timestamp>
  <contributor>
    <ip>143.105.193.119</ip>
  </contributor>
  <comment>/* Sources */</comment>
  <sha1>2zkdnl9nsd1fbopv0fpwu2j5gdf0haw</sha1>
  <text xml:space="preserve" bytes="1436">'''Aratrum''' is the Latin word for  [[plough]], and &quot;arotron&quot; (αροτρον) is the [[Greek language|Greek]] word. The   [[Ancient Greece|Greeks]] appear to have had diverse kinds of plough from the earliest  historical records. [[Hesiod]] advised the farmer to have always two ploughs, so that if  one broke the other might be ready for use. These ploughs should be of two kinds, the one  called &quot;autoguos&quot; (αυτογυος, &quot;self-limbed&quot;), in which the plough-tail  was of the same piece of timber as the share-beam and the pole; and the other called  &quot;pekton&quot; (πηκτον, &quot;fixed&quot;), because in it, three parts, which were of  three kinds of timber, were adjusted to one another, and fastened together by nails.

The ''autoguos'' plough was made from a [[sapling]] with two branches growing from its   trunk in opposite directions. In ploughing, the trunk served as the pole, one of the two     branches stood upwards and became the tail, and the other penetrated the ground and,    sometimes shod with bronze or iron, acted as the [[ploughshare]]. 

==Sources==
Based on an article from ''A Dictionary of Greek and Roman Antiquities,'' John Murray,     London, 1875.
ἄρατρον

==External links==
*[http://penelope.uchicago.edu/Thayer/E/Roman/Texts/secondary/SMIGRA*/Aratrum.html Smith's     Dictionary article], with diagrams, further details, sources.
[[Category:Agricultural machinery]]
[[Category:Ancient Greece]]
[[Category:Animal equipment]]</text>
</revision>
</page>

I've also tried iterparse and then printing the tag of the element it finds:

for e in etree.iterparse(file_name):
    print e.tag

but it complains about the e not having a tag attribute.

EDIT:

解决方案

The problem is that you are not taking XML namespaces into account. The XML document (and all the elements in it) is in the http://www.mediawiki.org/xml/export-0.7/ namespace. To make it work, you need to change

titles = document.findall('.//title')

to

titles = document.findall('.//{http://www.mediawiki.org/xml/export-0.7/}title')

The namespace can also be provided via the namespaces parameter:

NSMAP = {'mw':'http://www.mediawiki.org/xml/export-0.7/'}
titles = document.findall('.//mw:title', namespaces=NSMAP)

This works in Python 2.7, but it is not explained in the Python 2.7 documentation (the Python 3.3 documentation is better).

See also http://effbot.org/zone/element-namespaces.htm and this SO question with answer: Parsing XML with namespace in Python via 'ElementTree'.

---

The trouble with iterparse() is caused by the fact that this function provides (event, element) tuples (not just elements). In order to get the tag name, change

for e in etree.iterparse(file_name):
    print e.tag

to this:

for e in etree.iterparse(file_name):
    print e[1].tag

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