A convention we've used elsewhere is to set the default in `common.py`, and then have the `AUTH_TOKENS.get` use that default as it's default.

So, `common.py` would have `THIRD_PARTY_AUTH = {}`, and `aws.py` would have `THIRD_PARTY_AUTH = AUTH_TOKENS.get('THIRD_PARTY_AUTH', THIRD_PARTY_AUTH)`. That way, when your other code assumes that `settings.THIRD_PARTY_AUTH` is available, it won't be surprised.

Otherwise, you have to use `getattr(settings, THIRD_PARTY_AUTH, {})`, to handle the case where maybe you're not in either dev.py or aws.py.