Question

I would like to store some information at the “request scope” when using google app engine (python). What I mean by this is that I would like to initialize some information when a request is first received, and then be able to access it from anywhere for the life of the request (and only from that request).

An example of this would be if I saved the current user’s name at request scope after they were authenticated.

How would I go about doing this sort of thing?

Thanks!

Answer 1

A pattern used in app engine itself seems to be threading.local which you can grep for in the SDK code. Making os.environ request local is done like that in runtime/request_environment.py for example.

A rough example:

import threading

class _State(threading.local):
    """State keeps track of request info"""
    user = None

_state = _State()

From elsewhere you could authenticate early on in handler code.

from state import _state
if authentication_passed:
    _state.user = user

and provide convenience that can be used in other parts of your code

from state import _state
def get_authenticated_user():
    user = _state.user
    if not user:
        raise AuthenticationError()
    return user