urllib3

Highlights

Re-use the same socket connection for multiple requests (HTTPConnectionPool and HTTPSConnectionPool) (with optional client-side certificate verification).
File posting (encode_multipart_formdata).
Built-in redirection and retries (optional).
Supports gzip and deflate decoding.
Thread-safe and sanity-safe.
Works with AppEngine, gevent, and eventlib.
Tested on Python 2.6+ and Python 3.3+, 100% unit test coverage.
Small and easy to understand codebase perfect for extending and building upon. For a more comprehensive solution, have a look at Requests which is also powered by urllib3.

What's wrong with urllib and urllib2?

There are two critical features missing from the Python standard library: Connection re-using/pooling and file posting. It's not terribly hard to implement these yourself, but it's much easier to use a module that already did the work for you.

The Python standard libraries urllib and urllib2 have little to do with each other. They were designed to be independent and standalone, each solving a different scope of problems, and urllib3 follows in a similar vein.

Why do I want to reuse connections?

Performance. When you normally do a urllib call, a separate socket connection is created with each request. By reusing existing sockets (supported since HTTP 1.1), the requests will take up less resources on the server's end, and also provide a faster response time at the client's end. With some simple benchmarks (see test/benchmark.py ), downloading 15 URLs from google.com is about twice as fast when using HTTPConnectionPool (which uses 1 connection) than using plain urllib (which uses 15 connections).

This library is perfect for:

Talking to an API
Crawling a website
Any situation where being able to post files, handle redirection, and retrying is useful. It's relatively lightweight, so it can be used for anything!

Examples

Go to urllib3.readthedocs.org for more nice syntax-highlighted examples.

But, long story short:

import urllib3

http = urllib3.PoolManager()

r = http.request('GET', 'http://google.com/')

print r.status, r.data

The PoolManager will take care of reusing connections for you whenever you request the same host. For more fine-grained control of your connection pools, you should look at ConnectionPool.

Run the tests

We use some external dependencies to run the urllib3 test suite. Easiest way to run the tests is thusly from the urllib3 source root:

$ pip install -r test-requirements.txt
$ nosetests
.....................................................

Success! You could also pip install coverage to get code coverage reporting.

Contributing

Check for open issues or open a fresh issue to start a discussion around a feature idea or a bug. There is a Contributor Friendly tag for issues that should be ideal for people who are not very familiar with the codebase yet.
Fork the urllib3 repository on Github to start making your changes.
Write a test which shows that the bug was fixed or that the feature works as expected.
Send a pull request and bug the maintainer until it gets merged and published. :) Make sure to add yourself to CONTRIBUTORS.txt.