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Redis/Memcached sessions for Tornado

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README.markdown

pycket

This is a session library, written for use with Redis or Memcached, and Tornado web server.

Status of the project

Build Status

License

This software is under BSD 2-Clause License (see LICENSE file)

Requirements

Non-Python requirements:

  • Redis (tested with version 2.4.0) or Memcached (tested with version 1.4.7)

Python requirements (included in setup script)

  • Tornado (tested with 2.1.1, installable via "tornado" package in PyPI)

Python requirements (not included, because depend on the datastore that you wish to use)

  • redis-py (tested with 2.4.9, installable via "redis" package in PyPI)
  • python-memcached (tested with 1.47, installable via "python-memcached" package in PyPI)

Installing

If you use virtualenv:

$ pip install pycket

If you don't and your site-packages are shared for all users in your machine:

$ sudo pip install pycket

If you don't have any idea of what pip is (shame on you!), or can't use it:

$ easy_install pycket

or, after downloading (here) and unpacking the .tar.gz/.zip package:

$ python setup.py install

Development requirements

If you wish to contribute to the project as a developer, just install the requirements file included in the project with pip.

Examples

You have two ways of using pycket sessions in your application (please refer to the "Settings" section below before starting to use).

The easier way is including the appropriate mixin(s) in the handler's inheritance list, and the "session" member will become available:

from pycket.session import SessionMixin


class MyHandler(tornado.web.RequestHandler, SessionMixin):
    def get(self):
        self.session.set('foo', ['bar', 'baz'])
        foo = self.session.get('foo') # will get back the list ['bar', 'baz']

The other way (harder, but less coupled) is to instantiate a SessionManager and passing the handler instance to the initializer:

from pycket.session import SessionManager


class MyHandler(tornado.web.RequestHandler):
    def get(self):
        session = SessionManager(self)
        session.set('foo', ['bar', 'baz'])
        foo = session.get('foo') # will get back the list ['bar', 'baz']

For both examples above the session instance is a SessionManager.

SessionManager instances act as a dictionary, so they can retrieve values with a default alternative, like:

session.get("this doesn't exist", "so give me this instead")

and they can also get and set values with square-brackets, like:

session['gimme'] = 'Fire!'
print session['gimme'] # 'Fire!'

Settings

pycket understands two types of settings, which must be items in the application's settings:

  1. ["pycket"]: the base settings dictionary for pycket;
  2. ["pycket"]["engine"]: the only mandatory setting. Must be "redis" or "memcached";
  3. ["pycket"]["storage"]: this is a dictionary containing any items that should be repassed to the redis.Redis or memcached.Client to be used in the session manager (such as "host", "port", "servers" etc); Notice that for Redis, however, that if you want to change the dataset numbers to be used for sessions and notifications, use "db_sessions" and "db_notifications", respectively, instead of "db" (they will be converted to the "db" parameter that is passed to the Redis client for each manager afterwards);
  4. ["pycket"]["cookies"]: this is a dictionary containing all settings to be repassed to the RequestHandler.set_secure_cookie. If they don't contain "expires" or "expires_days" items, they will be set as None, which means that the default behaviour for the sessions is to last on browser session. (And deleted as soon as the user closes the browser.) Notice that the sessions in the database last for one day, though.

Example using Redis:

application = tornado.web.Application([
    (r'/', MainHandler),
], **{
    'pycket': {
        'engine': 'redis',
        'storage': {
            'host': 'localhost',
            'port': 6379,
            'db_sessions': 10,
            'db_notifications': 11,
        },
        'cookies': {
            'expires_days': 120,
        },
    },
)

Example using Memcached:

application = tornado.web.Application([
    (r'/', MainHandler),
], **{
    'pycket': {
        'engine': 'memcached',
        'storage': {
            'servers': ('localhost:11211',)
        },
        'cookies': {
            'expires_days': 120,
        },
    },
)

The default Redis dataset numbers for sessions and notifications are, respectively, 0 and 1, and the default Memcached servers tuple is ("localhost:11211",)

Notifications

This feature is almost equal to the sessions, but slightly different:

  • They have to be used via pycket.notification.NotificationMixin or pycket.notification.NotificationManager;
  • The values persisted with them can be retrieved only once, and after this are immediately deleted from the datastore;
  • The default Redis dataset used is 1, instead of 0, to avoid conflicts with normal sessions.
  • Unfortunately, for Memcached, the notifications are saved in the same datastore as the sessions, because I still didn't find a way keep them in a separate datastore.

Connection pooling (Redis)

(Thanks @whardier for this hint! :-)

It's also possible to pass a Redis connection pool to the storage backend, so that you avoid having an open connection for each Redis access.

Suppose you want to keep only one open connection, you can do something like this:

pycket_pool = redis.ConnectionPool(max_connections=1, host='localhost', port=6379)
#...
            **{
                'pycket': {
                    'engine': 'redis',
                    'storage': {
                        'connection_pool': pycket_pool,
                        'db_sessions': 10,
                        'db_notifications': 11,
                    },
                    'cookies': {
                        'expires_days': 120,
                    },
                },
            }
#...

Author

This module was developed by Diogo Baeder (*/diogobaeder), who is an absolute Python lover, and is currently in love with event-driven programming and ArchLinux.

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