Common Techniques for Python Web Crawling: GET/POST, Proxies, Cookies, Headers, Captcha, Gzip, and Multithreading

Python is most often used for rapid web development, web crawling, and automation; this guide summarizes reusable crawling techniques to save time.

1. Basic page fetching – Demonstrates using GET and POST methods to retrieve web pages.

2. Using proxy IPs – Shows how to configure urllib2.ProxyHandler to route requests through proxy servers when the original IP is blocked.

3. Cookie handling – Explains the purpose of cookies, introduces the cookielib module, and describes how CookieJar() manages cookies in memory without manual intervention.

4. Spoofing as a browser – Details adding custom headers such as User-Agent and Content-Type to avoid 403 errors and to satisfy server expectations.

5. Captcha processing – Provides simple strategies for recognizing basic captchas and mentions using third‑party services for complex ones like 12306.

6. Gzip compression – Shows how to add an Accept‑Encoding: gzip header to request compressed responses and how to decompress the data.

7. Multithreaded concurrent fetching – Presents a simple thread‑pool template that prints numbers 1‑10 to illustrate concurrent execution, noting that Python threading can still improve crawling speed despite the GIL.