session.py

import uuid

class SessionNotFound(Exception):
    pass


class InMemoryStore:
    """ not thread-safe ;-) """
    def __init__(self):
        self.sessions = {}

    def get(self, sid):
        data = self.sessions.get(sid, None)
        if data is None:
            raise SessionNotFound
        return data

    def exists(self, sid):
        return sid in self.sessions

    def set(self, sid, data):
        self.sessions[sid] = data

    def delete(self, sid):
        del self.sessions[sid]


class SessionMiddleware:
    def __init__(self, store, cookie_name='sid'):
        self.store = store
        self.cookie_name = cookie_name

    def generate_sid(self):
        return str(uuid.uuid4())

    def process_request(self, request, response):
        sid = request.cookies.get(self.cookie_name, None)
        if sid is not None:
            try:
                data = self.store.get(sid)
            except SessionNotFound:
                return
            request.context.update(data)

    def process_response(self, request, response, resource):
        sid = request.cookies.get(self.cookie_name, None)
        if sid is None:
            sid = self.generate_sid()
            response.set_cookie(self.cookie_name, sid, secure=False)

        self.store.set(sid, request.context)