Server-side Sessions with Redis | Flask (A Python Microframework)

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　　Server-side Sessions with Redis | Flask (A Python Microframework)

Server-side Sessions with Redis
By Armin Ronacher filed in Sessions
　　If you need to store a lot of session data it makes sense to move the data from the cookie to the server. In that case you might want to use redis as the storage backend for the actual session data.
　　The following code implements a session backend using redis. It allows you to either pass in a redis client or will connect to the redis instance on localhost. All the keys are prefixed with a specified prefix which defaults to session:.

import pickle
from datetime import timedelta
from uuid import uuid4
from redis import Redis
from werkzeug.datastructures import CallbackDict
from flask.sessions import SessionInterface, SessionMixin

class RedisSession(CallbackDict, SessionMixin):
def __init__(self, initial=None, sid=None, new=False):
def on_update(self):
self.modified = True
CallbackDict.__init__(self, initial, on_update)
self.sid = sid
self.new = new
self.modified = False

class RedisSessionInterface(SessionInterface):
serializer = pickle
session_class = RedisSession
def __init__(self, redis=None, prefix='session:'):
if redis is None:
redis = Redis()
self.redis = redis
self.prefix = prefix
def generate_sid(self):
return str(uuid4())
def get_redis_expiration_time(self, app, session):
if session.permanent:
return app.permanent_session_lifetime
return timedelta(days=1)
def open_session(self, app, request):
sid = request.cookies.get(app.session_cookie_name)
if not sid:
sid = self.generate_sid()
return self.session_class(sid=sid, new=True)
val = self.redis.get(self.prefix + sid)
if val is not None:
data = self.serializer.loads(val)
return self.session_class(data, sid=sid)
return self.session_class(sid=sid, new=True)
def save_session(self, app, session, response):
domain = self.get_cookie_domain(app)
if not session:
self.redis.delete(self.prefix + session.sid)
if session.modified:
response.delete_cookie(app.session_cookie_name,
domain=domain)
return
redis_exp = self.get_redis_expiration_time(app, session)
cookie_exp = self.get_expiration_time(app, session)
val = self.serializer.dumps(dict(session))
self.redis.setex(self.prefix + session.sid, val,
int(redis_exp.total_seconds()))
response.set_cookie(app.session_cookie_name, session.sid,
expires=cookie_exp, httponly=True,
domain=domain)
　　Here is how to enable it:

app = Flask(__name__)
app.session_interface = RedisSessionInterface()
　　If you get an attribute error that total_seconds is missing it means you're using a version of Python older than 2.7. In this case you can use this function as a replacement for the total_seconds method:

def total_seconds(td):
return td.days * 60 * 60 * 24 + td.seconds
　　This snippet by Armin Ronacher can be used freely for anything you like. Consider it public domain.