文章目录
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JavaScript
1.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 json
import string
import downloader
def 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 json
import csv
import downloader
def 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.html
import downloader
try:
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 QWebView
except ImportError:
from PyQt4.QtGui import QApplication
from PyQt4.QtCore import QUrl, QEventLoop, QTimer
from PyQt4.QtWebKit import QWebView
def 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 countries
if __name__ == '__main__':
main()
# -*- coding: utf-8 -*-
import re
import csv
import time
try:
from PySide.QtGui import QApplication
from PySide.QtCore import QUrl, QEventLoop, QTimer
from PySide.QtWebKit import QWebView
except ImportError:
from PyQt4.QtGui import QApplication
from PyQt4.QtCore import QUrl, QEventLoop, QTimer
from PyQt4.QtWebKit import QWebView
import lxml.html
class 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 webdriver
def 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 countries
if __name__ == '__main__':
main()
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【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
