该内容改编自 http://flask.pocoo.org/snippets/75/.

如果您需要存储大量会话数据，则可以将数据从cookie移至服务器.在这种情况下，您可能希望将redis用作实际会话数据的存储后端.

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.

以下代码使用Redis实现了会话后端.它允许您传入Redis客户端或连接到本地主机上的Redis实例.所有键都以指定的前缀作为前缀，默认前缀为session:.

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)

以下是启用它的方法:

app = Flask(__name__)
app.session_interface = RedisSessionInterface()

如果您收到缺少total_seconds的属性错误，则意味着您使用的Python版本早于2.7.在这种情况下，您可以使用此函数代替total_seconds方法:

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