Web scraping blocking is a technical measure taken by websites to prevent crawlers from automatically scraping their web content. The main purpose of blocking web scraping mechanisms is to protect the website's data and resources from being maliciously crawled or abused, thereby maintaining the normal operation of the website and user experience.

In crawler development, common obstacles to web scraping are mainly the following:

• User-Agent field: detect the user's request header, which can be bypassed by disguising the header. ‌

• IP: detect the number of requests of a certain IP in a unit time, and stop its request if it exceeds the threshold. Use proxy IP pool to bypass this restriction. ‌

• Cookies: need to simulate login, and then crawl data after successfully obtaining cookies. ‌
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• Verification code: can be cracked by coding platform or simulated user behavior to bypass. ‌

• Dynamic page: data is generated through ajax request or JavaScript, and can be bypassed by simulating browser behavior using tools such as Selenium or PhantomJS. ‌
  In crawler development, common obstacles to web scraping are mainly the following:

  How to disguise headers to avoid web scraping blockage?

You can adopt the following strategies:

• Simulate a browser‌: Add or modify the User-Agent field to make it look like a real browser request rather than a crawler program.
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• Forge access address: Set the Referer field to simulate the user's behavior of linking from one page to another, bypassing the detection based on Referer.

In specific implementation, you can add or modify headers in the crawler request, for example, using Python's requests library:

import requests

headers = {
    'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3',
    'Referer': 'https://www.example.com/'
}

response = requests.get('https://www.targetwebsite.com/', headers=headers)

How to set up a proxy server for web scraping?

Setting up a proxy server for web scraping can be accomplished by following these steps:

‌1.Choose the appropriate proxy server‌

Ensure the stability and reliability of the proxy server, select the appropriate proxy type (such as HTTP, HTTPS, SOCKS5, etc.) according to the requirements of the target website, and ensure that the speed and bandwidth of the proxy server meet the requirements of web scraping need.

‌2.Get proxy server information‌

Get the IP address, port number, and possible username and password of the proxy server.

‌Set proxy in web scraping code‌:

• When using the ‌requests library‌, you can specify the address and port of the proxy server through the proxies parameter. For example:

proxies = {
    'http': 'http://IP address:Port number',
    'https': 'https://IP address:Port number',
}
response = requests.get('Destination URL', proxies=proxies)

• When using the ‌urllib library‌, you need to set up the proxy through ProxyHandler and build a custom opener object. ‌Verify the validity of the proxy‌: Before the crawler runs, verify whether the proxy is valid by sending a test request to avoid using an invalid proxy that causes the crawler to fail.

Through the above steps, you can effectively set up a proxy server for the crawler to use, improving the stability and concealment of the crawler.

Conclusion

Web scraping barriers are technical measures set up by websites to prevent automatic crawlers, such as IP restrictions, user agent detection, captcha verification, etc. These mechanisms will limit crawlers' access, reduce data collection efficiency, and even lead to crawlers being banned.

To bypass these mechanisms, a variety of strategies can be adopted, such as using proxy IPs, simulating user behavior, and cracking verification codes. Among them, using proxy IPs is one of the most common strategies, which can hide the real IP address of the crawler, disperse the request load, and reduce the risk of being banned.