17: Transient Data Using Sessions¶
Store and retrieve non-permanent data in Pyramid sessions.
Background¶
When people use your web application, they frequently perform a task that requires semi-permanent data to be saved. For example, a shopping cart. This is called a session.
Pyramid has basic built-in support for sessions. Third party packages such as
pyramid_redis_sessions
provide richer session support. Or you can create
your own custom sessioning engine. Let's take a look at the
built-in sessioning support.
Objectives¶
- Make a session factory using a built-in, simple Pyramid sessioning system
- Change our code to use a session
Steps¶
First we copy the results of the
view_classes
step:$ cd ..; cp -r view_classes sessions; cd sessions $ $VENV/bin/python setup.py develop
Our
sessions/tutorial/__init__.py
needs a choice of session factory to get registered with the configurator:1 2 3 4 5 6 7 8 9 10 11 12 13 14
from pyramid.config import Configurator from pyramid.session import SignedCookieSessionFactory def main(global_config, **settings): my_session_factory = SignedCookieSessionFactory( 'itsaseekreet') config = Configurator(settings=settings, session_factory=my_session_factory) config.include('pyramid_chameleon') config.add_route('home', '/') config.add_route('hello', '/howdy') config.scan('.views') return config.make_wsgi_app()
Our views in
sessions/tutorial/views.py
can now userequest.session
:1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
from pyramid.view import ( view_config, view_defaults ) @view_defaults(renderer='home.pt') class TutorialViews: def __init__(self, request): self.request = request @property def counter(self): session = self.request.session if 'counter' in session: session['counter'] += 1 else: session['counter'] = 1 return session['counter'] @view_config(route_name='home') def home(self): return {'name': 'Home View'} @view_config(route_name='hello') def hello(self): return {'name': 'Hello View'}
The template at
sessions/tutorial/home.pt
can display the value:1 2 3 4 5 6 7 8 9 10
<!DOCTYPE html> <html lang="en"> <head> <title>Quick Tutorial: ${name}</title> </head> <body> <h1>Hi ${name}</h1> <p>Count: ${view.counter}</p> </body> </html>
Make sure the tests still pass:
$ $VENV/bin/nosetests tutorial
Run your Pyramid application with:
$ $VENV/bin/pserve development.ini --reload
Open http://localhost:6543/ and http://localhost:6543/howdy in your browser. As you reload and switch between those URLs, note that the counter increases and is not specific to the URL.
Restart the application and revisit the page. Note that counter still increases from where it left off.
Analysis¶
Pyramid's request object now has a session
attribute
that we can use in our view code. It acts like a dictionary.
Since all the views are using the same counter, we made the counter a Python property at the view class level. With this, each reload will increase the counter displayed in our template.
In web development, "flash messages" are notes for the user that need
to appear on a screen after a future web request. For example,
when you add an item using a form POST
, the site usually issues a
second HTTP Redirect web request to view the new item. You might want a
message to appear after that second web request saying "Your item was
added." You can't just return it in the web response for the POST,
as it will be tossed out during the second web request.
Flash messages are a technique where messages can be stored between requests, using sessions, then removed when they finally get displayed.
See also