The Role and Principle of Proxies

In web crawlers, the role of a proxy is to hide the real IP address to prevent being blocked or restricted from accessing the target website. By using a proxy server, the crawler can change the place where the request is sent to achieve the purpose of anonymously accessing the website.

The principle of proxy is to set the address and port of the proxy server in the crawler program, so that when the crawler initiates a network request, it first passes through the proxy server and then sends the request to the target website. This can make the target website mistakenly think that the proxy server is accessing it, thus achieving the purpose of hiding the real IP.

Common ways to use proxies

There are two main ways that web crawlers can utilize proxies: directly using proxy IPs and self-built proxy pools.

Directly using proxy IP means that the crawler program obtains some proxy IP addresses in advance and then randomly selects a proxy IP to send the request when initiating the request. This way is simple and direct, but you need to update the proxy IP list regularly, because many proxy IPs will be blocked or invalidated.

Self-constructed proxy pool means that the crawler program saves the proxy IPs obtained by crawling proxy websites or purchasing proxy services in a proxy pool, and then obtains proxy IPs from the pool to use when it needs to send requests. This approach is relatively stable, but requires a certain maintenance cost.

Proxy Usage Examples

The following is sample code for using proxies in a Python crawler program:

import requests

proxy = {
"http": "http://127.0.0.1:8888",
"https": "http://127.0.0.1:8888"
}

url = "https://www.example.com"
response = requests.get(url, proxies=proxy)
print(response.text)

In this example, we set the address and port of a proxy server through the requests library and then send a GET request with a proxy to the target website. This will realize the effect of web crawlers using proxies for access.

With proxies, web crawlers can better hide their real IP addresses from blocking or restricting access, as well as better respond to anti-crawler tactics on target sites.