pyspider爬虫学习-教程3-Render-with-PhantomJS.md

Level 3: Render with PhantomJS
==============================
#有时web页面太复杂，无法找到API请求。现在是时候迎接[PhantomJS]的力量了
Sometimes web page is too complex to find out the API request. It's time to meet the power of [PhantomJS].
#使用PhantomJS,你应该已经安装PhantomJS(http://phantomjs.org/download.html)。如果你运行的是'all'模式的pyspider，如果在“路径”中有excutable，则会启用PhantomJS。
To use PhantomJS, you should have PhantomJS [installed](http://phantomjs.org/download.html). If you are running pyspider with `all` mode, PhantomJS is enabled if excutable in the `PATH`.
#确保phantomjs正在运行
Make sure phantomjs is working by running
```
$ pyspider phantomjs
```
如果输出是Web服务器运行在25555端口上，则继续教程的其余部分
Continue with the rest of the tutorial if the output is
```
Web server running on port 25555
```
#使用PhantomJS
Use PhantomJS
-------------
#
#当pyspider与PhantomJS连接在一起时，您可以通过向'self.crawl'添加一个参数“fetch_type='js'”来启用这个特性。我们使用PhantomJS获取频道列表[http://www.twitch.tv/directory/game/Dota%202](http://www.twitch.tv/directory/game/Dota%202)中使用AJAX加载我们讨论[Level 2](tutorial/AJAX-and-more-HTTP#ajax):
When pyspider with PhantomJS connected, you can enable this feature by adding a parameter `fetch_type='js'` to `self.crawl`. We use PhantomJS to scrape channel list of  [http://www.twitch.tv/directory/game/Dota%202](http://www.twitch.tv/directory/game/Dota%202) which is loaded with AJAX we discussed in [Level 2](tutorial/AJAX-and-more-HTTP#ajax):

```
class Handler(BaseHandler):
def on_start(self):
self.crawl('http://www.twitch.tv/directory/game/Dota%202',
fetch_type='js', callback=self.index_page)

def index_page(self, response):
return {
"url": response.url,
"channels": [{
"title": x('.title').text(),
"viewers": x('.info').contents()[2],
"name": x('.info a').text(),
} for x in response.doc('.stream.item').items()]
}
```
#我使用了一些API来处理流列表。你可以找到完整的API参考[PyQuery完整的API](https://pythonhosted.org/pyquery/api.html)
> I used some API to handle the list of streams. You can find complete API reference from [PyQuery complete API](https://pythonhosted.org/pyquery/api.html)

#在页面运行JavaScript脚本
Running JavaScript on Page
--------------------------
#在这一部分中我们将尝试截取图像[http://www.pinterest.com/categories/popular/](http://www.pinterest.com/categories/popular/)。在开始时，只有25个图像显示，当你滚动到页面底部时，会加载更多的图片。
We will try to scrape images from [http://www.pinterest.com/categories/popular/](http://www.pinterest.com/categories/popular/) in this section. Only 25 images is shown at the beginning, more images would be loaded when you scroll to the bottom of the page.
#我们可以使用[`js_script` parameter](/apis/self.crawl/#enable-javascript-fetcher-need-support-by-fetcher)来对图像进行尽可能多的抓取，设置一些JavaScript代码包装的函数来模拟滚动操作
To scrape images as many as posible we can use a [`js_script` parameter](/apis/self.crawl/#enable-javascript-fetcher-need-support-by-fetcher) to set some function wrapped JavaScript codes to simulate the scroll action:

```
class Handler(BaseHandler):
def on_start(self):
self.crawl('http://www.pinterest.com/categories/popular/',
fetch_type='js', js_script="""
function() {
window.scrollTo(0,document.body.scrollHeight);
}
""", callback=self.index_page)

def index_page(self, response):
return {
"url": response.url,
"images": [{
"title": x('.richPinGridTitle').text(),
"img": x('.pinImg').attr('src'),
"author": x('.creditName').text(),
} for x in response.doc('.item').items() if x('.pinImg')]
}
```
# 脚本在加载页面后执行(可以通过[`js_run_at` parameter](/apis/self.crawl/#enable-javascript-fetcher-need-support-by-fetcher)进行更改)。
> * Script would been executed after page loaded(can been changed via [`js_run_at` parameter](/apis/self.crawl/#enable-javascript-fetcher-need-support-by-fetcher))
#我们滚动页面加载后,你可以滚动多次在[`setTimeout`]时间内(https://developer.mozilla.org/en-US/docs/Web/API/WindowTimers.setTimeout)。PhantomJS将在超时之前获取尽可能多的项目。
> * We scroll once after page loaded, you can scroll multiple times using [`setTimeout`](https://developer.mozilla.org/en-US/docs/Web/API/WindowTimers.setTimeout). PhantomJS will fetch as many items as possible before timeout arrived.
#在线实例
Online demo: [http://demo.pyspider.org/debug/tutorial_pinterest](http://demo.pyspider.org/debug/tutorial_pinterest)

[PhantomJS]:           http://phantomjs.org/[/code]