Short sample to use cookie mechanism to make a session on a GAE app.

main.py

#!/usr/bin/env python
#
import Cookie
import datetime
import hashlib
import logging
import os

from google.appengine.api import memcache
from google.appengine.ext import db
from google.appengine.ext import webapp
from google.appengine.ext.webapp import util
from google.appengine.ext.webapp import template

class SeedInteger(db.Model):
    value = db.IntegerProperty()

SEED_KEY = 'HelloWorld'
HW_SESSION_KEY = 'hwsessionid'

def get_seed_from_datastore():
    seed = db.get(db.Key.from_path('SeedInteger', SEED_KEY))
    if not seed:
        seed = SeedInteger(key_name=SEED_KEY)
        seed.value = 1
    elif seed.value < 9223372036854775807: # 2 ** 63 - 1
        # db.IntegerProperty can hold integers with 64 bits.
        seed.value += 1
    else:
        seed.value = 1
    seed.put()
    return seed.value

def generate_session_id():
    seed = get_seed_from_datastore()
    logging.info("Seed for hash: %s" % str(seed))
    m = hashlib.sha1()
    m.update(datetime.datetime.now().isoformat())
    m.update(str(seed))
    logging.info("SHA1: %s" % m.hexdigest())
    return m.hexdigest()

class Item(object):
    def __init__(self, name, value):
        self.name = name
        self.value = value

class MainHandler(webapp.RequestHandler):
    def __init__(self):
        self.session_id = None
        self.content = []

    def get(self):
        back = (self.request.get('back', default_value='') != '')

        self.session_id = self.get_session_id()
        if self.session_id is None or self.session_id == '':
            self.session_id = generate_session_id()
            cookie = Cookie.SimpleCookie()
            cookie[HW_SESSION_KEY] = self.session_id
            expiration = datetime.datetime.now() + datetime.timedelta(seconds=300)
            cookie[HW_SESSION_KEY]['expires'] = expiration.strftime('%a, %d-%b-%Y %H:%M:%S GMT')
            self.response.headers.add_header('Set-Cookie', cookie.output(header=''))

        data = self.get_data()
        if not back:
            data += 1
        elif data > 0:
            data -= 1
        self.set_data(data)

        self.content.append(Item('hash seed', get_seed_from_datastore()))
        self.content.append(Item('session id', self.session_id))
        self.content.append(Item('cookies', self.request.cookies))
        self.content.append(Item('data in memcache', '%s' % str(data)))
        values = {
            'content': self.content,
            }
        path = os.path.join(os.path.dirname(__file__), 'main.html')
        self.response.out.write(template.render(path, values))

    def get_session_id(self):
        value = None
        if HW_SESSION_KEY in self.request.cookies:
            value = self.request.cookies[HW_SESSION_KEY]
            logging.info("%s: %s" % (HW_SESSION_KEY, type(value)))
        return value

    def get_data(self):
        data = memcache.get(self.session_id)
        if data is not None:
            return data
        else:
            data = 0
            memcache.add(self.session_id, data, 60)
            return data

    def set_data(self, data):
        memcache.set(self.session_id, data, 60)

def main():
    application = webapp.WSGIApplication([('/', MainHandler)], debug=True)
    util.run_wsgi_app(application)


if __name__ == '__main__':
    main()