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Web Session Usage

Status:Work in progress

Why Use Sessions?

Sessions are a common way to keep simple browsing data attached to a user’s browser. This is generally used to store simple data that does not need to be persisted in a database.

Sessions in TurboGears can be backed by the filesystem, memcache, the database, or by hashed cookie values. By default the filesystem is used, but in high traffic websites hashed cookies provide a great system for small bits of session data. If you are storing lots of data in the session, Memcache is recommended.

How To Use Sessions?

If you just quickstarted a TurboGears 2 application, the session system is pre-configured and ready to be used.

By default we are using the Beaker session system. This system is configured to use file system based storage.

Each time a client connects, the session middleware (Beaker) will inspect the cookie using the cookie name we have defined in the configuration file.

If the cookie is not found it will be set in the browser. On all subsequent visits, the middleware will find the cookie and make use of it.

In the cookie beaker stores, a large random key was set at the first visit and was been associated behind the scenes to a file in the file system cache. In all but the cookie based backends, this key is then used to lookup and retrieve the session data from the proper datastore.

OK, enough with theory! Let’s get to some real life (sort of) examples. Open up your root controller and add the following import at the top the file:

from tg import session

What you get is a Session instance that is always request-local, in other words, it’s the session for this particular user. The session can be manipulated in much the same way as a standard python dictionary.

Here is how you search for a key in the session:

if session.get('mysuperkey', None):
    # do something intelligent
    pass

and here is how to set a key in the session:

session['mysuperkey'] = 'some python data I need to store'
session.save()

You should note that you need to explicitly save the session in order for your keys to be stored in the session.

You can delete all user session with the delete() method of the session object:

session.delete()

Even though it’s not customary to delete all user sessions on a production environment, you will typically do it for cleaning up after usability or functional tests.