Advanced Usage¶

Session Objects¶

The Session object allows you to persist certain parameters across requests. It also perstists 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.content
# '{"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.

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

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 it’s 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!

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

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]>]

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

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

def hack_headers(args):
    if not args[headers]:
        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/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.

When you pass our authentication tuple to a request method, the first string is the type of authentication. ‘basic’ is inferred if none is provided.

You can pass in a callable object instead of a string for the first item in the tuple, and it will be used in place of the built in authentication callbacks.

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.

We simply need to define a callback function that will be used to update the Request object, right before it is dispatched.

def pizza_auth(r, username):
    """Attaches HTTP Pizza Authentication to the given Request object.
    """
    r.headers['X-Pizza'] = username

    return r

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

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

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]>