问题

I'm trying to develop a simple web scraper. I want to extract text without the HTML code. In fact, I achieve this goal, but I have seen that in some pages where JavaScript is loaded I didn't obtain good results.

For example, if some JavaScript code adds some text, I can't see it, because when I call

response = urllib2.urlopen(request)

I get the original text without the added one (because JavaScript is executed in the client).

So, I'm looking for some ideas to solve this problem.

回答1:

EDIT 30/Dec/2017: This answer appears in top results of Google searches, so I decided to update it. The old answer is still at the end.

dryscape isn't maintained anymore and the library dryscape developers recommend is Python 2 only. I have found using Selenium's python library with Phantom JS as a web driver fast enough and easy to get the work done.

Once you have installed Phantom JS, make sure the phantomjs binary is available in the current path:

phantomjs --version
# result:
2.1.1

Example

To give an example, I created a sample page with following HTML code. (link):

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Javascript scraping test</title>
</head>
<body>
  <p id='intro-text'>No javascript support</p>
  <script>
     document.getElementById('intro-text').innerHTML = 'Yay! Supports javascript';
  </script> 
</body>
</html>

without javascript it says: No javascript support and with javascript: Yay! Supports javascript

Scraping without JS support:

import requests
from bs4 import BeautifulSoup
response = requests.get(my_url)
soup = BeautifulSoup(response.text)
soup.find(id="intro-text")
# Result:
<p id="intro-text">No javascript support</p>

Scraping with JS support:

from selenium import webdriver
driver = webdriver.PhantomJS()
driver.get(my_url)
p_element = driver.find_element_by_id(id_='intro-text')
print(p_element.text)
# result:
'Yay! Supports javascript'

You can also use Python library dryscrape to scrape javascript driven websites.

Scraping with JS support:

import dryscrape
from bs4 import BeautifulSoup
session = dryscrape.Session()
session.visit(my_url)
response = session.body()
soup = BeautifulSoup(response)
soup.find(id="intro-text")
# Result:
<p id="intro-text">Yay! Supports javascript</p>

回答2:

We are not getting the correct results because any javascript generated content needs to be rendered on the DOM. When we fetch an HTML page, we fetch the initial, unmodified by javascript, DOM.

Therefore we need to render the javascript content before we crawl the page.

As selenium is already mentioned many times in this thread (and how slow it gets sometimes was mentioned also), I will list two other possible solutions.

Solution 1: This is a very nice tutorial on how to use Scrapy to crawl javascript generated content and we are going to follow just that.

What we will need:

Docker installed in our machine. This is a plus over other solutions until this point, as it utilizes an OS-independent platform.
Install Splash following the instruction listed for our corresponding OS.
Quoting from splash documentation:

Splash is a javascript rendering service. It’s a lightweight web browser with an HTTP API, implemented in Python 3 using Twisted and QT5.

Essentially we are going to use Splash to render Javascript generated content.
Run the splash server: sudo docker run -p 8050:8050 scrapinghub/splash.
Install the scrapy-splash plugin: pip install scrapy-splash
Assuming that we already have a Scrapy project created (if not, let's make one), we will follow the guide and update the settings.py:
Then go to your scrapy project’s settings.py and set these middlewares:
```
DOWNLOADER_MIDDLEWARES = {
      'scrapy_splash.SplashCookiesMiddleware': 723,
      'scrapy_splash.SplashMiddleware': 725,
      'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware': 810,
}
```
The URL of the Splash server(if you’re using Win or OSX this should be the URL of the docker machine: How to get a Docker container's IP address from the host?):
```
SPLASH_URL = 'http://localhost:8050'
```
And finally you need to set these values too:
```
DUPEFILTER_CLASS = 'scrapy_splash.SplashAwareDupeFilter'
HTTPCACHE_STORAGE = 'scrapy_splash.SplashAwareFSCacheStorage'
```

Finally, we can use a SplashRequest:

In a normal spider you have Request objects which you can use to open URLs. If the page you want to open contains JS generated data you have to use SplashRequest(or SplashFormRequest) to render the page. Here’s a simple example:
class MySpider(scrapy.Spider):
    name = "jsscraper"
    start_urls = ["http://quotes.toscrape.com/js/"]

    def start_requests(self):
        for url in self.start_urls:
        yield SplashRequest(
            url=url, callback=self.parse, endpoint='render.html'
        )

    def parse(self, response):
        for q in response.css("div.quote"):
        quote = QuoteItem()
        quote["author"] = q.css(".author::text").extract_first()
        quote["quote"] = q.css(".text::text").extract_first()
        yield quote
SplashRequest renders the URL as html and returns the response which you can use in the callback(parse) method.

Solution 2: Let's call this experimental at the moment (May 2018)...
This solution is for Python's version 3.6 only (at the moment).

Do you know the requests module (well who doesn't)?
Now it has a web crawling little sibling: requests-HTML:

This library intends to make parsing HTML (e.g. scraping the web) as simple and intuitive as possible.

Install requests-html: pipenv install requests-html

Make a request to the page's url:

from requests_html import HTMLSession

session = HTMLSession()
r = session.get(a_page_url)

Render the response to get the Javascript generated bits:
```
r.html.render()
```

Finally, the module seems to offer scraping capabilities.
Alternatively, we can try the well-documented way of using BeautifulSoup with the r.html object we just rendered.

回答3:

Maybe selenium can do it.

from selenium import webdriver
import time

driver = webdriver.Firefox()
driver.get(url)
time.sleep(5)
htmlSource = driver.page_source

回答4:

If you have ever used the Requests module for python before, I recently found out that the developer created a new module called Requests-HTML which now also has the ability to render JavaScript.

You can also visit https://html.python-requests.org/ to learn more about this module, or if your only interested about rendering JavaScript then you can visit https://html.python-requests.org/?#javascript-support to directly learn how to use the module to render JavaScript using Python.

Essentially, Once you correctly install the Requests-HTML module, the following example, which is shown on the above link, shows how you can use this module to scrape a website and render JavaScript contained within the website:

from requests_html import HTMLSession
session = HTMLSession()

r = session.get('http://python-requests.org/')

r.html.render()

r.html.search('Python 2 will retire in only {months} months!')['months']

'<time>25</time>' #This is the result.

I recently learnt about this from a YouTube video. Click Here! to watch the YouTube video, which demonstrates how the module works.

回答5:

This seems to be a good solution also, taken from a great blog post

import sys  
from PyQt4.QtGui import *  
from PyQt4.QtCore import *  
from PyQt4.QtWebKit import *  
from lxml import html 

#Take this class for granted.Just use result of rendering.
class Render(QWebPage):  
  def __init__(self, url):  
    self.app = QApplication(sys.argv)  
    QWebPage.__init__(self)  
    self.loadFinished.connect(self._loadFinished)  
    self.mainFrame().load(QUrl(url))  
    self.app.exec_()  

  def _loadFinished(self, result):  
    self.frame = self.mainFrame()  
    self.app.quit()  

url = 'http://pycoders.com/archive/'  
r = Render(url)  
result = r.frame.toHtml()
# This step is important.Converting QString to Ascii for lxml to process

# The following returns an lxml element tree
archive_links = html.fromstring(str(result.toAscii()))
print archive_links

# The following returns an array containing the URLs
raw_links = archive_links.xpath('//div[@class="campaign"]/a/@href')
print raw_links

回答6:

It sounds like the data you're really looking for can be accessed via secondary URL called by some javascript on the primary page.

While you could try running javascript on the server to handle this, a simpler approach to might be to load up the page using Firefox and use a tool like Charles or Firebug to identify exactly what that secondary URL is. Then you can just query that URL directly for the data you are interested in.

回答7:

Selenium is the best for scraping JS and Ajax content.

Check this article for extracting data from the web using Python

$ pip install selenium

Then download Chrome webdriver.

from selenium import webdriver

browser = webdriver.Chrome()

browser.get("https://www.python.org/")

nav = browser.find_element_by_id("mainnav")

print(nav.text)

Easy, right?

回答8:

You can also execute javascript using webdriver.

from selenium import webdriver

driver = webdriver.Firefox()
driver.get(url)
driver.execute_script('document.title')

or store the value in a variable

result = driver.execute_script('var text = document.title ; return var')

回答9:

I personally prefer using scrapy and selenium and dockerizing both in separate containers. This way you can install both with minimal hassle and crawl modern websites that almost all contain javascript in one form or another. Here's an example:

Use the scrapy startproject to create your scraper and write your spider, the skeleton can be as simple as this:

import scrapy


class MySpider(scrapy.Spider):
    name = 'my_spider'
    start_urls = ['https://somewhere.com']

    def start_requests(self):
        yield scrapy.Request(url=self.start_urls[0])


    def parse(self, response):

        # do stuff with results, scrape items etc.
        # now were just checking everything worked

        print(response.body)

The real magic happens in the middlewares.py. Overwrite two methods in the downloader middleware, __init__ and process_request, in the following way:

# import some additional modules that we need
import os
from copy import deepcopy
from time import sleep

from scrapy import signals
from scrapy.http import HtmlResponse
from selenium import webdriver

class SampleProjectDownloaderMiddleware(object):

def __init__(self):
    SELENIUM_LOCATION = os.environ.get('SELENIUM_LOCATION', 'NOT_HERE')
    SELENIUM_URL = f'http://{SELENIUM_LOCATION}:4444/wd/hub'
    chrome_options = webdriver.ChromeOptions()

    # chrome_options.add_experimental_option("mobileEmulation", mobile_emulation)
    self.driver = webdriver.Remote(command_executor=SELENIUM_URL,
                                   desired_capabilities=chrome_options.to_capabilities())


def process_request(self, request, spider):

    self.driver.get(request.url)

    # sleep a bit so the page has time to load
    # or monitor items on page to continue as soon as page ready
    sleep(4)

    # if you need to manipulate the page content like clicking and scrolling, you do it here
    # self.driver.find_element_by_css_selector('.my-class').click()

    # you only need the now properly and completely rendered html from your page to get results
    body = deepcopy(self.driver.page_source)

    # copy the current url in case of redirects
    url = deepcopy(self.driver.current_url)

    return HtmlResponse(url, body=body, encoding='utf-8', request=request)

Dont forget to enable this middlware by uncommenting the next lines in the settings.py file:

DOWNLOADER_MIDDLEWARES = {
'sample_project.middlewares.SampleProjectDownloaderMiddleware': 543,}

Next for dockerization. Create your Dockerfile from a lightweight image (I'm using python Alpine here), copy your project directory to it, install requirements:

# Use an official Python runtime as a parent image
FROM python:3.6-alpine

# install some packages necessary to scrapy and then curl because it's  handy for debugging
RUN apk --update add linux-headers libffi-dev openssl-dev build-base libxslt-dev libxml2-dev curl python-dev

WORKDIR /my_scraper

ADD requirements.txt /my_scraper/

RUN pip install -r requirements.txt

ADD . /scrapers

And finally bring it all together in docker-compose.yaml:

version: '2'
services:
  selenium:
    image: selenium/standalone-chrome
    ports:
      - "4444:4444"
    shm_size: 1G

  my_scraper:
    build: .
    depends_on:
      - "selenium"
    environment:
      - SELENIUM_LOCATION=samplecrawler_selenium_1
    volumes:
      - .:/my_scraper
    # use this command to keep the container running
    command: tail -f /dev/null

Run docker-compose up -d. If you're doing this the first time it will take a while for it to fetch the latest selenium/standalone-chrome and the build your scraper image as well.

Once it's done, you can check that your containers are running with docker ps and also check that the name of the selenium container matches that of the environment variable that we passed to our scraper container (here, it was SELENIUM_LOCATION=samplecrawler_selenium_1).

Enter your scraper container with docker exec -ti YOUR_CONTAINER_NAME sh , the command for me was docker exec -ti samplecrawler_my_scraper_1 sh, cd into the right directory and run your scraper with scrapy crawl my_spider.

The entire thing is on my github page and you can get it from here

回答10:

You'll want to use urllib, requests, beautifulSoup and selenium web driver in your script for different parts of the page, (to name a few).
Sometimes you'll get what you need with just one of these modules.
Sometimes you'll need two, three, or all of these modules.
Sometimes you'll need to switch off the js on your browser.
Sometimes you'll need header info in your script.
No websites can be scraped the same way and no website can be scraped in the same way forever without having to modify your crawler, usually after a few months. But they can all be scraped! Where there's a will there's a way for sure.
If you need scraped data continuously into the future just scrape everything you need and store it in .dat files with pickle.
Just keep searching how to try what with these modules and copying and pasting your errors into the Google.

回答11:

A mix of BeautifulSoup and Selenium works very well for me.

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from bs4 import BeautifulSoup as bs

driver = webdriver.Firefox()
driver.get("http://somedomain/url_that_delays_loading")
    try:
        element = WebDriverWait(driver, 10).until(
        EC.presence_of_element_located((By.ID, "myDynamicElement"))) #waits 10 seconds until element is located. Can have other wait conditions  such as visibility_of_element_located or text_to_be_present_in_element

        html = driver.page_source
        soup = bs(html, "lxml")
        dynamic_text = soup.find_all("p", {"class":"class_name"}) #or other attributes, optional
    else:
        print("Couldnt locate element")

P.S. You can find more wait conditions here

回答12:

Using PyQt5

from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import QUrl
from PyQt5.QtWebEngineWidgets import QWebEnginePage
import sys
import bs4 as bs
import urllib.request


class Client(QWebEnginePage):
    def __init__(self,url):
        global app
        self.app = QApplication(sys.argv)
        QWebEnginePage.__init__(self)
        self.html = ""
        self.loadFinished.connect(self.on_load_finished)
        self.load(QUrl(url))
        self.app.exec_()

    def on_load_finished(self):
        self.html = self.toHtml(self.Callable)
        print("Load Finished")

    def Callable(self,data):
        self.html = data
        self.app.quit()

# url = ""
# client_response = Client(url)
# print(client_response.html)

来源：https://stackoverflow.com/questions/56685116/extracting-content-from-a-dynamic-web-site-using-a-java-library

标签

python

web-scraping

python-2.x

urlopen

Web-scraping JavaScript page with Python

问题

回答1:

Example

Scraping without JS support:

Scraping with JS support:

Scraping with JS support:

回答2:

回答3:

回答4:

回答5:

回答6:

回答7:

回答8:

回答9:

回答10:

回答11:

回答12: