How do I keep state between requests in AppEngine (Python)?
The ways to reliable keep state between requests are memcache, the datastore or through the user (cookies or post/get).
You can use the runtime cache too, but this is very unreliable as you don't know if a request will end up in the same runtime or the runtime can drop it's entire cache if it feels like it.
I really wouldn't use the runtime cache except for very specific situations, for example I use it to cache the serialization of objects to json as that is pretty slow and if the caching is gone I can regenerate the result easily.
I'm writing a simple app with AppEngine, using Python. After a successful insert by a user and redirect, I'd like to display a flash confirmation message on the next page. 
What's the best way to keep state between one request and the next? Or is this not possible because AppEngine is distributed? I guess, the underlying question is whether AppEngine provides a persistent session object. 
Thanks
Hannes