Mastering Sessions Cookies with Python Requests

Cookies and sessions are essential for effective web scraping. When sites use cookies for authentication or tracking, scrapers need to properly handle them. With Python's excellent Requests library, it's straightforward to leverage sessions and cookies for robust scraping. In this guide, we'll cover the key techniques.

Creating a Session

First, instantiate a Requests Session object:

import requests
session = requests.Session()

This session will retain cookies and settings across requests.

Persisting Cookies

The main benefit of sessions is automatic cookie persistence. Normally cookies disappear after each request, but sessions retain them:

# First request sets a cookie
response = session.get('<http://website.com/login>')

# Second request automatically has the cookie
response = session.get('<http://website.com/user-page>')

This allows you to scrape content across multiple pages as if logged in.

Direct Cookie Access

Sometimes you need to directly access cookie values:

session_cookies = session.cookies.get_dict()
print(session_cookies['UserID'])

You can also inspect domain, path, expiry, etc. This gives you precision when required.

Setting Custom Cookies

When a site expects certain cookies, you can set them:

session.cookies.set('name', 'value', domain='website.com')

Then this cookie will automatically be sent by the session.

Persisting Other Settings

You can also persist headers, proxies, and authentication using the session:

# Headers
session.headers.update({'User-Agent': 'Scraper'})

# Proxies
session.proxies = {'http': '<http://10.10.1.10:3128>'}

# Authentication
session.auth = ('user', 'pass')

This keeps your code DRY and readable.

Saving Cookies to Files

For long-running scrapers, you may want to periodically save cookie jars to files:

import json

with open('cookies.json', 'w') as f:
  json.dump(session.cookies.get_dict(), f)

And then restore cookies later:

with open('cookies.json') as f:
  cookies = json.load(f)
  session.cookies.update(cookies)

This retains scraper state across executions.

Conclusion

Sessions give you ultimate control over cookies, headers, proxies and more. By mastering session techniques, you can scrape complex sites requiring authentication and state management.

FAQs

How do sessions differ from global cookies?

Sessions maintain an isolated cookie jar that won't overwrite your global browser cookies.

Can sessions work across different domains?

Cross-domain sessions depend on server configuration. Some cookies won't persist across domains.

What's the best way to persist a scraper's state?

Save cookie jars to files periodically to retain state across long-running scrapers.

How can I debug cookie issues?

Inspect Response.cookies, Response.headers, and Session.cookies.get_dict() to diagnose problems.

Is Requests thread-safe?

Requests sessions are not inherently thread-safe. Consider a multithreading model if needed.

By leveraging sessions, you can write resilient, maintainable scrapers capable of handling complex cookie-driven sites. Follow these patterns to level up your scraping game!