Sessions

An essential feature for a web application is the ability to store specific informations about the client from a request to the next one. Accordingly to this need, Emmett provides another object beside the request and the response ones called session.

from emmett import session

@app.route("/counter")
async def count():
    session.counter = (session.counter or 0) + 1
    return "This is your %d visit" % session.counter

The above code is quite simple: the app increments the counter every time the user visit the page and return this number to the user.
Basically, you can use session object to store and retrieve data, but before you can do that, you should add a SessionManager to your application pipeline. These managers allows you to store sessions' data on different storage systems, depending on your needs. Let's see them in detail.

Storing sessions in cookies

Changed in version 2.3

You can store session contents directly in the cookies of the client using the Emmett's SessionManager.cookies pipe:

from emmett import App, session
from emmett.sessions import SessionManager

app = App(__name__)
app.pipeline = [SessionManager.cookies('myverysecretkey')]

@app.route("/counter")
# previous code

As you can see, SessionManager.cookies needs a secret key to crypt the sessions' data and keep them secure – you should choose a good key – but also accepts more parameters:

Note: in order to use modern value for encryption_mode, you need to install Emmett with crypto extra. This module is written in Rust language, so in case no pre-build wheel is available for your platform, you will need Rust toolchain on your system to compile it from source.

Storing sessions on filesystem

Changed in version 2.1

You can store session contents on the server's filesystem using the Emmett's SessionManager.files pipe:

from emmett import App, session
from emmett.sessions import SessionManager

app = App(__name__)
app.pipeline = [SessionManager.files()]

@app.route("/counter")
# previous code

As you can see, SessionManager.files doesn't require specific parameters, but it accepts these optional ones:

Storing sessions using redis

Changed in version 2.1

You can store session contents using redis – you obviously need the redis package for python – with the Emmett's SessionManager.redis pipe:

from redis import Redis
from emmett import App, session
from emmett.sessions import SessionManager

app = App(__name__)
red = Redis(host='127.0.0.1', port=6379)
app.pipeline = [SessionManager.redis(red)]

@app.route("/counter")
# previous code

As you can see SessionManager.redis needs a redis connection as first parameter, but as for the cookie manager, it also accepts more parameters:

The expire parameter tells redis when to auto-delete the unused session: every time the session is updated, the expiration time is reset to the one specified.