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SessionsΒΆ

Pyramid uses Beaker sessions just like Pylons, but they’re not enabled by default. To use them you’ll have to add the “pyramid_beaker” package as a dependency, and put the following line in your main() function:

config.include("pyramid_beaker")

(To add a dependency, put it in the requires list in setup.py, and reinstall the application.)

The default configuration is in-memory sessions and (I think) no caching. You can customize this by putting configuration settings in your INI file or in the settings dict at the beginning of the main() function (before the Configurator is instantiated). The Akhet Demo configures Beaker with the following settings, borrowed from the Pylons configuration:

# Beaker cache
cache.regions = default_term, second, short_term, long_term
cache.type = memory
cache.second.expire = 1
cache.short_term.expire = 60
cache.default_term.expire = 300
cache.long_term.expire = 3600

# Beaker sessions
#session.type = file
#session.data_dir = %(here)s/data/sessions/data
#session.lock_dir = %(here)s/data/sessions/lock
session.type = memory
session.key = akhet_demo
session.secret = 0cb243f53ad865a0f70099c0414ffe9cfcfe03ac

To use file-based sessions like in Pylons, uncomment the first three session settings and comment out the “session.type = memory” line.

You should set the “session.secret=” setting to a random string. It’s used to digitally sign the session cookie to prevent session hijacking.

Beaker has several persistence backends available, including memory, files, SQLAlchemy, memcached, and cookies (which stores each session variable in a client-side cookie, and has size limitationss). The most popular deployment backend nowadays is memcached, which can act as a shared storage between several processes and servers, thus providing the speed of memory with the ability to scale to a multi-server cluster. Pylons defaults to disk-based sessions.

Beaker plugs into Pyramid’s built-in session interface, which is accessed via request.session. Use it like a dict. Unlike raw Beaker sessions, you don’t have to call session.save() every time you change something, but you should call session.changed() if you’ve modified a mutable item in the session; e.g., session["mylist"].append(1).

The Pyramid session interface also has some extra features. It can store a set of “flash messages” to display on the next page view, which is useful when you want to push a success/failure message and redirect, and the message will be displayed on the target page. It’s based on webhelpers.flash, which is incompatible with Pyramid because it depends on Pylons’ magic globals. There are also methods to set a secure form token, which prevent form submissions that didn’t come from a form requested earlier in the session (and thus may be a cross-site forgery attack). (Note: flash messages are not related to the Adobe Flash movie player.)

See the Sessions chapter in the Pyramid manual for the API of all these features and other features. The Beaker manual will help you configure a backend. The Akhet Demo is an example of using Pyramid with Beaker, and has flash messages.

Note: I sometimes get an exception in the debug toolbar when sessions are enabled. They may be a code discrepency between the distributions. If this happens to you, you can disable the toolbar until the problem is fixed.

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