# Session Basics

Sessions are the most complicated topic covered in this series of examples, and because of that it is going to take a few examples to cover all of the different aspects. This first example demonstrates the very basics of the Twisted Web session API: how to get the session object for the current request and how to prematurely expire a session.

Before diving into the APIs, let’s look at the big picture of sessions in Twisted Web. Sessions are represented by instances of `Session` . The `Site` creates a new instance of `Session` the first time an application asks for it for a particular session. `Session` instances are kept on the `Site` instance until they expire (due to inactivity or because they are explicitly expired). Each time after the first that a particular session’s `Session` object is requested, it is retrieved from the `Site` .

With the conceptual underpinnings of the upcoming API in place, here comes the example. This will be a very simple rpy script which tells a user what its unique session identifier is and lets it prematurely expire the session.

First, we’ll import `Resource` so we can define a couple of subclasses of it:

    from twisted.web.resource import Resource

Next we’ll define the resource which tells the client what its session identifier is. This is done easily by first getting the session object using `Request.getSession` and then getting the session object’s uid attribute:

    class ShowSession(Resource):
        def render_GET(self, request):
            return b'Your session id is: ' + request.getSession().uid

To let the client expire its own session before it times out, we’ll define another resource which expires whatever session it is requested with. This is done using the `Session.expire` method:

    class ExpireSession(Resource):
        def render_GET(self, request):
            request.getSession().expire()
            return b'Your session has been expired.'

Finally, to make the example an rpy script, we’ll make an instance of `ShowSession` and give it an instance of `ExpireSession` as a child using `Resource.putChild` :

    resource = ShowSession()
    resource.putChild(b"expire", ExpireSession())

And that is the complete example. You can fire this up and load the top page. You’ll see a (rather opaque) session identifier that remains the same across reloads (at least until you flush the `TWISTED_SESSION` cookie from your browser or enough time passes). You can then visit the `expire` child and go back to the top page and see that you have a new session.

Here’s the complete source for the example:

    from twisted.web.resource import Resource

    class ShowSession(Resource):
        def render_GET(self, request):
            return b'Your session id is: ' + request.getSession().uid

    class ExpireSession(Resource):
        def render_GET(self, request):
            request.getSession().expire()
            return b'Your session has been expired.'

    resource = ShowSession()
    resource.putChild(b"expire", ExpireSession())