动态网页示例对加载内容进行逆向工程1通过开发者工具的逆向工程2通过墨盒测试的逆向工程21搜索条件为空时22用号匹配时22用号匹配时渲染动态网页1使用WebKit渲染引擎2使用Selenium自定义渲染
现在大部分的主流网站都用javaScript动态显示网页内容，这样使得我们之前提取技术无法正常运行。本篇将介绍两种提取基于JS动态网页的数据。
Javascript逆向工程渲染JavaScript1.动态网页示例
我们先看一个动态网页的示例。在示例网站的中，我们从http://127.0.0.1:8000/places/default/search 搜索国家名包涵A的表单。 我们根据按F12开发者工具显示的标签，用lxml模块提取数据，发现提取不到什么数据。
>>> import lxml.html>>> from downloader import Downloader>>> D=Downloader()>>> html=D('http://127.0.0.1:8000/places/default/search')Downloading: http://127.0.0.1:8000/places/default/search>>> tree=lxml.html.fromstring(html)>>> tree.CSSselect('div#result a')[]>>> 我们在浏览器右击查看网页源代码发现我们要提取的div数据是空的。
...<div id="results"></div>...这是因为F12的开发者工具是显示的标签是网页当前的状态，也就是使用JavaScript动态加载完搜索结果之后的网页。
2.对加载内容进行逆向工程
由于这些网页的数据是JS动态加载的，要想提取该数据，我们需要网页如何加载该数据的，该过程也被称为逆向工程。
2.1通过开发者工具的逆向工程
我们在上节F12的开发者工具的Network发现Ajax响应一个json文件，即：http://127.0.0.1:8000/places/ajax/search.json?&search_term=A&page_size=10&page=0 。AJAX响应的返回数据是JSON格式的，因此我们可以使用Python的json模块将解析为一个字典。
>>> import json>>> html=D('http://127.0.0.1:8000/places/ajax/search.json?&search_term=A&page_size=10&page=0')Downloading: http://127.0.0.1:8000/places/ajax/search.json?&search_term=A&page_size=10&page=0>>> json.loads(html){u'records': [ {u'PRetty_link': u'<div><a href="/places/default/view/Afghanistan-1"><img src="/places/static/images/flags/af.png" /> Afghanistan</a></div>', u'country': u'Afghanistan', u'id': 3781}, {u'pretty_link': u'<div><a href="/places/default/view/Aland-Islands-2"><img src="/places/static/images/flags/ax.png" /> Aland Islands</a></div>', u'country': u'Aland Islands', u'id': 3782},...], u'num_pages': 22, u'error': u''}>>> 我们可以通过分页请求提取json数据存到txt文件中。分页请求会让同一个国家在多次搜索返回多次，但通过set()集合会过滤重复的元素。
# -*- coding: utf-8 -*-import jsonimport stringimport downloaderdef main(): template_url = 'http://127.0.0.1:8000/places/ajax/search.json?&page={}&page_size=10&search_term={}' countries = set() download = downloader.Downloader() for letter in string.lowercase: page = 0 while True: html = download(template_url.format(page, letter)) try: ajax = json.loads(html) except ValueError as e: print e ajax = None else: for record in ajax['records']: countries.add(record['country']) page += 1 if ajax is None or page >= ajax['num_pages']: break open('2countries2.txt', 'w').write('/n'.join(sorted(countries)))if __name__ == '__main__': main()2.2通过墨盒测试的逆向工程
在不知道源代码的情况下的测试称为墨盒测试。我们可以使用一次搜索查询就能匹配所有结果，接下来，我们将尝试使用不同字符测试这种想法是否可行。
2.2.1搜索条件为空时
>>> import json>>> from downloader import Downloader>>> D=Downloader()>>> url='http://127.0.0.1:8000/places/ajax/search.json?&page_size=10&page=0&search_term='>>> json.loads(D(url))['num_pages']Downloading: http://127.0.0.1:8000/places/ajax/search.json?&page_size=10&page=0&search_term=0>>> 搜索条件为空时，这种方法并没有奏效。
2.2.2用*号匹配时
>>> json.loads(D(url+'*'))['num_pages']Downloading: http://127.0.0.1:8000/places/ajax/search.json?&page_size=10&page=0&search_term=*0用*号匹配时，这种方法也没有奏效。
2.2.2用.号匹配时
>>> json.loads(D(url+'.'))['num_pages']Downloading: http://127.0.0.1:8000/places/ajax/search.json?&page_size=10&page=0&search_term=.26这种方法测试成功了，看来服务器是通过正则表达式进行匹配的。在搜索界面中包含4、10、20这几种选项，其中默认值是10。我们增加显示数量进行测试。
>>> url='http://127.0.0.1:8000/places/ajax/search.json?&page_size=20&page=0&search_term='>>> json.loads(D(url+'.'))['num_pages']Downloading: http://127.0.0.1:8000/places/ajax/search.json?&page_size=20&page=0&search_term=.13>>> url='http://127.0.0.1:8000/places/ajax/search.json?&page_size=1000&page=0&search_term='>>> json.loads(D(url+'.'))['num_pages']Downloading: http://127.0.0.1:8000/places/ajax/search.json?&page_size=1000&page=0&search_term=.1>>> 我们如下整合过完整代码。
# -*- coding: utf-8 -*-import jsonimport csvimport downloaderdef main(): writer = csv.writer(open('2.2countries.csv', 'w')) D = downloader.Downloader() #html = D('http://example.webscraping.com/ajax/search.json?page=0&page_size=1000&search_term=.') html = D('http://127.0.0.1:8000/places/ajax/search.json?&page_size=1000&page=0&search_term=.') ajax = json.loads(html) for record in ajax['records']: writer.writerow([record['country']])if __name__ == '__main__': main()3.渲染动态网页
一些网站用Google Web Toolkit（GWT）工具开发的，产生的JS代码是压缩的，但可以通过JSbeautifier工具进行还原，但逆向工程效果不是很好。渲染引擎是浏览器加载网页时解析HTML、应用CSS样式并执行JS语句进行渲染显示。本节中我们使用WebKit渲染引擎，并通过Qt框架获得引擎的一个便捷Python接口，也可以用Selenium自定义渲染。
3.1使用WebKit渲染引擎
<html> <body> <div id="result"></div> <script>document.getElementById("result").innerText = 'Hello World';</script> </body></html># -*- coding: utf-8 -*-import lxml.htmlimport downloadertry: from PySide.QtGui import * from PySide.QtCore import * from PySide.QtWebKit import *except ImportError: from PyQt4.QtGui import * from PyQt4.QtCore import * from PyQt4.QtWebKit import *def direct_download(url): download = downloader.Downloader() return download(url)def webkit_download(url): app = Qapplication([]) webview = QWebView() loop=QEventLoop() webview.loadFinished.connect(loop.quit) webview.load(QUrl(url)) app.exec_() # delay here until download finished return webview.page().mainFrame().toHtml()def parse(html): tree = lxml.html.fromstring(html) print tree.cssselect('#result')[0].text_content()def main(): url = 'http://127.0.0.1:8000/places/default/dynamic' #url = 'http://example.webscraping.com/dynamic' parse(direct_download(url)) parse(webkit_download(url)) return print len(r.html)if __name__ == '__main__': main()# -*- coding: utf-8 -*-try: from PySide.QtGui import QApplication from PySide.QtCore import QUrl, QEventLoop, QTimer from PySide.QtWebKit import QWebViewexcept ImportError: from PyQt4.QtGui import QApplication from PyQt4.QtCore import QUrl, QEventLoop, QTimer from PyQt4.QtWebKit import QWebViewdef main(): app = QApplication([]) webview = QWebView() loop = QEventLoop() webview.loadFinished.connect(loop.quit) webview.load(QUrl('http://127.0.0.1:8000/places/default/dynamic')) #webview.load(QUrl('http://example.webscraping.com/search')) loop.exec_() webview.show() frame = webview.page().mainFrame() frame.findFirstElement('#search_term').setAttribute('value', '.') frame.findFirstElement('#page_size option:checked').setPlainText('1000') frame.findFirstElement('#search').evaluateJavaScript('this.click()') elements = None while not elements: app.processEvents() elements = frame.findAllElements('#results a') countries = [e.toPlainText().strip() for e in elements] print countriesif __name__ == '__main__': main()# -*- coding: utf-8 -*-import reimport csvimport timetry: from PySide.QtGui import QApplication from PySide.QtCore import QUrl, QEventLoop, QTimer from PySide.QtWebKit import QWebViewexcept ImportError: from PyQt4.QtGui import QApplication from PyQt4.QtCore import QUrl, QEventLoop, QTimer from PyQt4.QtWebKit import QWebViewimport lxml.htmlclass BrowserRender(QWebView): def __init__(self, display=True): self.app = QApplication([]) QWebView.__init__(self) if display: self.show() # show the browser def open(self, url, timeout=60): """Wait for download to complete and return result""" loop = QEventLoop() timer = QTimer() timer.setSingleShot(True) timer.timeout.connect(loop.quit) self.loadFinished.connect(loop.quit) self.load(QUrl(url)) timer.start(timeout * 1000) loop.exec_() # delay here until download finished if timer.isActive(): # downloaded successfully timer.stop() return self.html() else: # timed out print 'Request timed out:', url def html(self): """Shortcut to return the current HTML""" return self.page().mainFrame().toHtml() def find(self, pattern): """Find all elements that match the pattern""" return self.page().mainFrame().findAllElements(pattern) def attr(self, pattern, name, value): """Set attribute for matching elements""" for e in self.find(pattern): e.setAttribute(name, value) def text(self, pattern, value): """Set attribute for matching elements""" for e in self.find(pattern): e.setPlainText(value) def click(self, pattern): """Click matching elements""" for e in self.find(pattern): e.evaluateJavaScript("this.click()") def wait_load(self, pattern, timeout=60): """Wait for this pattern to be found in webpage and return matches""" deadline = time.time() + timeout while time.time() < deadline: self.app.processEvents() matches = self.find(pattern) if matches: return matches print 'Wait load timed out'def main(): br = BrowserRender() br.open('http://127.0.0.1:8000/places/default/dynamic') #br.open('http://example.webscraping.com/search') br.attr('#search_term', 'value', '.') br.text('#page_size option:checked', '1000') br.click('#search') elements = br.wait_load('#results a') writer = csv.writer(open('countries.csv', 'w')) for country in [e.toPlainText().strip() for e in elements]: writer.writerow([country])if __name__ == '__main__': main()3.2使用Selenium自定义渲染
from selenium import webdriverdef main(): driver = webdriver.Firefox() driver.get('http://127.0.0.1:8000/places/default/dynamic') #driver.get('http://example.webscraping.com/search') driver.find_element_by_id('search_term').send_keys('.') driver.execute_script("document.getElementById('page_size').options[1].text = '1000'"); driver.find_element_by_id('search').click() driver.implicitly_wait(30) links = driver.find_elements_by_css_selector('#results a') countries = [link.text for link in links] driver.close() print countriesif __name__ == '__main__': main()Wu_Being 博客声明：本人博客欢迎转载，请标明博客原文和原链接！谢谢！ 【Python爬虫系列】《【Python爬虫5】提取JS动态网页数据》http://blog.csdn.net/u014134180/article/details/55507014 Python爬虫系列的GitHub代码文件：https://github.com/1040003585/WebScrapingWithPython
