urllib3 Documentation

Highlights

Getting Started

Installing

pip install urllib3 or fetch the latest source from github.com/shazow/urllib3.

Usage

>>> import urllib3
>>> http = urllib3.PoolManager()
>>> r = http.request('GET', 'http://google.com/')
>>> r.status
200
>>> r.headers['server']
'gws'
>>> r.data
...

Components

urllib3 tries to strike a fine balance between power, extendability, and sanity. To achieve this, the codebase is a collection of small reusable utilities and abstractions composed together in a few helpful layers.

PoolManager

The highest level is the PoolManager(...).

The PoolManager will take care of reusing connections for you whenever you request the same host. this should cover most scenarios without significant loss of efficiency, but you can always drop down to a lower level component for more granular control.

>>> http = urllib3.PoolManager(10)
>>> r1 = http.request('GET', 'http://google.com/')
>>> r2 = http.request('GET', 'http://google.com/mail')
>>> r3 = http.request('GET', 'http://yahoo.com/')
>>> len(http.pools)
2

A PoolManager is a proxy for a collection of ConnectionPool objects. They both inherit from RequestMethods to make sure that their API is similar, so that instances of either can be passed around interchangeably.

ConnectionPool

The next layer is the ConnectionPool(...).

The HTTPConnectionPool and HTTPSConnectionPool classes allow you to define a pool of connections to a single host and make requests against this pool with automatic connection reusing and thread safety.

When the ssl module is available, then HTTPSConnectionPool objects can be configured to check SSL certificates against specific provided certificate authorities.

>>> conn = urllib3.connection_from_url('http://google.com')
>>> r1 = conn.request('GET', 'http://google.com/')
>>> r2 = conn.request('GET', '/mail')
>>> r3 = conn.request('GET', 'http://yahoo.com/')
Traceback (most recent call last)
  ...
HostChangedError: Connection pool with host 'http://google.com' tried to
open a foreign host: http://yahoo.com/

Again, a ConnectionPool is a pool of connections to a specific host. Trying to access a different host through the same pool will raise a HostChangedError exception unless you specify assert_same_host=False. Do this at your own risk as the outcome is completely dependent on the behaviour of the host server.

If you need to access multiple hosts and don’t want to manage your own collection of ConnectionPool objects, then you should use a PoolManager.

A ConnectionPool is composed of a collection of httplib.HTTPConnection objects.

Foundation

At the very core, just like its predecessors, urllib3 is built on top of httplib – the lowest level HTTP library included in the Python standard library.

To aid the limited functionality of the httplib module, urllib3 provides various helper methods which are used with the higher level components but can also be used independently.

Contributing

  1. 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.
  2. Fork the urllib3 repository on Github to start making your changes.
  3. Write a test which shows that the bug was fixed or that the feature works as expected.
  4. Send a pull request and bug the maintainer until it gets merged and published. :) Make sure to add yourself to CONTRIBUTORS.txt.

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