Advanced Usage

This document covers some of Requests more advanced features.

Session Objects

The Session object allows you to persist certain parameters across requests. It also persists cookies across all requests made from the Session instance.

A session object has all the methods of the main Requests API.

Let’s persist some cookies across requests:

s = requests.session()

s.get('http://httpbin.org/cookies/set/sessioncookie/123456789')
r = s.get("http://httpbin.org/cookies")

print r.text
# '{"cookies": {"sessioncookie": "123456789"}}'

Sessions can also be used to provide default data to the request methods:

headers = {'x-test': 'true'}
auth = ('user', 'pass')

with requests.session(auth=auth, headers=headers) as c:

    # both 'x-test' and 'x-test2' are sent
    c.get('http://httpbin.org/headers', headers={'x-test2': 'true'})

Any dictionaries that you pass to a request method will be merged with the session-level values that are set. The method-level parameters override session parameters.

Remove a Value From a Dict Parameter

Sometimes you’ll want to omit session-level keys from a dict parameter. To do this, you simply set that key’s value to None in the method-level parameter. It will automatically be omitted.

All values that are contained within a session are directly available to you. See the Session API Docs to learn more.

SSL Cert Verification

Requests can verify SSL certificates for HTTPS requests, just like a web browser. To check a host’s SSL certificate, you can use the verify argument:

>>> requests.get('https://kennethreitz.com', verify=True)
requests.exceptions.SSLError: hostname 'kennethreitz.com' doesn't match either of '*.herokuapp.com', 'herokuapp.com'

I don’t have SSL setup on this domain, so it fails. Excellent. Github does though:

>>> requests.get('https://github.com', verify=True)
<Response [200]>

You can also pass verify the path to a CA_BUNDLE file for private certs. You can also set the REQUESTS_CA_BUNDLE environment variable.

Body Content Workflow

By default, when you make a request, the body of the response isn’t downloaded immediately. The response headers are downloaded when you make a request, but the content isn’t downloaded until you access the Response.content attribute.

Let’s walk through it:

tarball_url = 'https://github.com/kennethreitz/requests/tarball/master'
r = requests.get(tarball_url)

The request has been made, but the connection is still open. The response body has not been downloaded yet.

r.content

The content has been downloaded and cached.

You can override this default behavior with the prefetch parameter:

r = requests.get(tarball_url, prefetch=True)
# Blocks until all of request body has been downloaded.

Configuring Requests

Sometimes you may want to configure a request to customize its behavior. To do this, you can pass in a config dictionary to a request or session. See the Configuration API Docs to learn more.

Keep-Alive

Excellent news — thanks to urllib3, keep-alive is 100% automatic within a session! Any requests that you make within a session will automatically reuse the appropriate connection!

Note that connections are only released back to the pool for reuse once all body data has been read; be sure to either set prefetch to True or read the content property of the Response object.

If you’d like to disable keep-alive, you can simply set the keep_alive configuration to False:

s = requests.session()
s.config['keep_alive'] = False

Asynchronous Requests

Requests has first-class support for concurrent requests, powered by gevent. This allows you to send a bunch of HTTP requests at the same time.

First, let’s import the async module. Heads up — if you don’t have gevent this will fail:

from requests import async

The async module has the exact same api as requests, except it doesn’t send the request immediately. Instead, it returns the Request object.

We can build a list of Request objects easily:

urls = [
    'http://python-requests.org',
    'http://httpbin.org',
    'http://python-guide.org',
    'http://kennethreitz.com'
]

rs = [async.get(u) for u in urls]

Now we have a list of Request objects, ready to be sent. We could send them one at a time with Request.send(), but that would take a while. Instead, we’ll send them all at the same time with async.map(). Using async.map() will also guarantee execution of the response hook, described below.

>>> async.map(rs)
[<Response [200]>, <Response [200]>, <Response [200]>, <Response [200]>]

Throttling

The map function also takes a size parameter, that specifies the number of connections to make at a time:

async.map(rs, size=5)

Event Hooks

Requests has a hook system that you can use to manipulate portions of the request process, or signal event handling.

Available hooks:

args:
A dictionary of the arguments being sent to Request().
pre_request:
The Request object, directly before being sent.
post_request:
The Request object, directly after being sent.
response:
The response generated from a Request.

You can assign a hook function on a per-request basis by passing a {hook_name: callback_function} dictionary to the hooks request parameter:

hooks=dict(args=print_url)

That callback_function will receive a chunk of data as its first argument.

def print_url(args):
    print args['url']

If an error occurs while executing your callback, a warning is given.

If the callback function returns a value, it is assumed that it is to replace the data that was passed in. If the function doesn’t return anything, nothing else is effected.

Let’s print some request method arguments at runtime:

>>> requests.get('http://httpbin.org', hooks=dict(args=print_url))
http://httpbin.org
<Response [200]>

Let’s hijack some arguments this time with a new callback:

def hack_headers(args):
    if args.get('headers') is None:
        args['headers'] = dict()

    args['headers'].update({'X-Testing': 'True'})

    return args

hooks = dict(args=hack_headers)
headers = dict(yo=dawg)

And give it a try:

>>> requests.get('http://httpbin.org/headers', hooks=hooks, headers=headers)
{
    "headers": {
        "Content-Length": "",
        "Accept-Encoding": "gzip",
        "Yo": "dawg",
        "X-Forwarded-For": "::ffff:24.127.96.129",
        "Connection": "close",
        "User-Agent": "python-requests.org",
        "Host": "httpbin.org",
        "X-Testing": "True",
        "X-Forwarded-Protocol": "",
        "Content-Type": ""
    }
}

Custom Authentication

Requests allows you to use specify your own authentication mechanism.

Any callable which is passed as the auth argument to a request method will have the opportunity to modify the request before it is dispatched.

Authentication implementations are subclasses of requests.auth.AuthBase, and are easy to define. Requests provides two common authentication scheme implementations in requests.auth: HTTPBasicAuth and HTTPDigestAuth.

Let’s pretend that we have a web service that will only respond if the X-Pizza header is set to a password value. Unlikely, but just go with it.

from requests.auth import AuthBase
class PizzaAuth(AuthBase):
    """Attaches HTTP Pizza Authentication to the given Request object."""
    def __init__(self, username):
        # setup any auth-related data here
        self.username = username

    def __call__(self, r):
        # modify and return the request
        r.headers['X-Pizza'] = self.username
        return r

Then, we can make a request using our Pizza Auth:

>>> requests.get('http://pizzabin.org/admin', auth=PizzaAuth('kenneth'))
<Response [200]>

Streaming Requests

With requests.Response.iter_lines() you can easily iterate over streaming APIs such as the Twitter Streaming API.

To use the Twitter Streaming API to track the keyword “requests”:

import requests
import json

r = requests.post('https://stream.twitter.com/1/statuses/filter.json',
    data={'track': 'requests'}, auth=('username', 'password'))

for line in r.iter_lines():
        if line: # filter out keep-alive new lines
                print json.loads(line)

Verbose Logging

If you want to get a good look at what HTTP requests are being sent by your application, you can turn on verbose logging.

To do so, just configure Requests with a stream to write to:

>>> my_config = {'verbose': sys.stderr}
>>> requests.get('http://httpbin.org/headers', config=my_config)
2011-08-17T03:04:23.380175   GET   http://httpbin.org/headers
<Response [200]>

Requests is an elegant and simple HTTP library for Python, built for human beings. You are currently looking at the documentation of the development release.

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