使用lxml在Python中遍历节点

Question

我有一个网页，正在用BeautifulSoup来解析，但速度有点慢，所以我决定试试lxml，因为我听说它非常快。

不过，我在让我的代码遍历我想要的部分时遇到了困难，不太确定怎么使用lxml，而且找不到清晰的文档。

这是我的代码：

import urllib, urllib2
from lxml import etree

def wgetUrl(target):
    try:
        req = urllib2.Request(target)
        req.add_header('User-Agent', 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.3 Gecko/2008092417 Firefox/3.0.3')
        response = urllib2.urlopen(req)
        outtxt = response.read()
        response.close()
    except:
        return ''
    return outtxt

newUrl = 'http://www.tv3.ie/3player'

data = wgetUrl(newUrl)
parser = etree.HTMLParser()
tree   = etree.fromstring(data, parser)

for elem in tree.iter("div"):
    print elem.tag, elem.attrib, elem.text

这段代码返回了所有的DIV，但我怎么才能只遍历id为'slider1'的那个呢？

div {'style': 'position: relative;', 'id': 'slider1'} None

这个方法不行：

for elem in tree.iter("slider1"):

我知道这可能是个傻问题，但我就是搞不明白……

谢谢！

* 编辑 **

在你的帮助下，加上这段代码后，我现在得到了下面的输出：

for elem in tree.xpath("//div[@id='slider1']//div[@id='gridshow']"):
    print elem[0].tag, elem[0].attrib, elem[0].text
    print elem[1].tag, elem[1].attrib, elem[1].text
    print elem[2].tag, elem[2].attrib, elem[2].text
    print elem[3].tag, elem[3].attrib, elem[3].text
    print elem[4].tag, elem[4].attrib, elem[4].text

输出：

a {'href': '/3player/show/392/57922/1/Tallafornia', 'title': '3player | Tallafornia, 11/01/2013. The Tallafornia crew are back, living in a beachside villa in Santa Ponsa, Majorca. As the crew settle in, the egos grow bigger than ever and cause tension'} None
h3 {} None
span {'id': 'gridcaption'} The Tallafornia crew are back, living in a beachside vill...
span {'id': 'griddate'} 11/01/2013
span {'id': 'gridduration'} 00:27:52

这些都很好，但我缺少了上面a标签的一部分。解析器是不是没有正确处理代码？

我没有得到以下内容：

<img alt="3player | Tallafornia, 11/01/2013. The Tallafornia crew are back, living in a beachside villa in Santa Ponsa, Majorca. As the crew settle in, the egos grow bigger than ever and cause tension" src='http://content.tv3.ie/content/videos/0378/tallaforniaep2_fri11jan2013_3player_1_57922_180x102.jpg' class='shadow smallroundcorner'></img>

有没有什么想法，为什么它没有提取到这个？

再次感谢，非常有帮助的帖子……

Answer 1

这是我自己让它工作的方式，我不确定这是不是最好的方法，欢迎大家评论：

import urllib2, re
from lxml import etree
from datetime import datetime

def wgetUrl(target):
    try:
        req = urllib2.Request(target)
        req.add_header('User-Agent', 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.3 Gecko/2008092417 Firefox/3.0.3')
        response = urllib2.urlopen(req)
        outtxt = response.read()
        response.close()
    except:
        return ''
    return outtxt

start = datetime.now()

newUrl = 'http://www.tv3.ie/3player' # homepage

data = wgetUrl(newUrl)
parser = etree.HTMLParser()
tree   = etree.fromstring(data, parser)

for elem in tree.xpath("//div[@id='slider1']//div[@id='gridshow'] | //div[@id='slider1']//div[@id='gridshow']//img[@class='shadow smallroundcorner']"):
    if elem.tag == 'img':
        img = elem.attrib.get('src')
        print 'img: ', img

    if elem.tag == 'div':
        show = elem[0].attrib.get('href')
        print 'show: ', show
        titleData = elem[0].attrib.get('title')

        match=re.search("3player\s+\|\s+(.+),\s+(\d\d/\d\d/\d\d\d\d)\.\s*(.*)", titleData) 
        title=match.group(1)
        print 'title: ', title

        description = match.group(3)
        print 'description: ', description

        date = elem[3].text
        duration = elem[4].text
        print 'date: ', date
        print 'duration: ', duration

end = datetime.now()
print 'time took was ', (end-start)

运行的时间还不错，虽然没有我预期的比BeautifulSoup快很多。

Answer 2

你可以使用以下的XPath表达式：

for elem in tree.xpath("//div[@id='slider1']"):

举个例子：

>>> import urllib2
>>> import lxml.etree
>>> url = 'http://www.tv3.ie/3player'
>>> data = urllib2.urlopen(url)
>>> parser = lxml.etree.HTMLParser()
>>> tree = lxml.etree.parse(data,parser)
>>> elem = tree.xpath("//div[@id='slider1']")
>>> elem[0].attrib
{'style': 'position: relative;', 'id': 'slider1'}

---

你需要更好地分析你正在处理的页面内容（一个好的方法是使用Firefox浏览器和Firebug插件）。

你想要获取的<img>标签其实是<a>标签的子标签：

>>> for elem in tree.xpath("//div[@id='slider1']//div[@id='gridshow']"):
...    for elem_a in elem.xpath("./a"):
...       for elem_img in elem_a.xpath("./img"):
...          print '<A> HREF=%s'%(elem_a.attrib['href'])
...          print '<IMG> ALT="%s"'%(elem_img.attrib['alt'])
<A> HREF=/3player/show/392/58784/1/Tallafornia
<IMG> ALT="3player | Tallafornia, 01/02/2013. A fresh romance blossoms in the Tallafornia house. Marc challenges Cormac to a 'bench off' in the gym"
<A> HREF=/3player/show/46/58765/1/Coronation-Street
<IMG> ALT="3player | Coronation Street, 01/02/2013. Tyrone bumps into Kirsty in the street and tries to take Ruby from her pram"
../..