July 2017
Intermediate to advanced
398 pages
11h 54m
Chinese
Content preview from Python数据处理
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246
｜
第
11
章
图 11-13：找到页面的元素
怎样编写
XPath
来选择它呢？实际上，有很多种方式。让我们从一个相当明显的方式开
始，使用带有
CSS
id
的
div
来编写
XPath
。用已学到的语法选择
div
：
'//div[@id="bottom_nav"]'
可以使用浏览器的
JavaScript
控制台测试这段代码。为了在控制台中测试
XPath
，直接将
它放在
$x();
中，这是一个
jQuery
控制台的实现，用于使用
XPath
浏览页面。让我们在控
制台中查看一下（见图
11-14
）。
1
图 11-14：使用控制台编写 XPath
我们有了合法的
XPath
来选择导航栏，因为控制台返回了一个对象（类似于
jQuery
选择
器）。但是我们真正想要的是链接。让我们来看一下怎样从这个
div
移到这些链接。我们
知道它们是后继，所以编写一个家族关系。
注
1
：
如果你想要在一个不使用
jQuery
的站点上使用
XPath
，需要使用
Mozilla
在文档中描述的不同语法
（
https://developer.mozilla.org/en-US/docs/Introduction_to_using_XPath_in_JavaScript
）。对于这个元素，
语法应该是
document.evaluate('//div[@id="bottom_nav"]', document)
。
网页抓取：获取并存储网络数据
｜
247
'//div[@id="bottom_nav"]/ul/li/a'
这里我们想要任何具有
id bottom_nav
的
divs ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.