Sqlalchemy before_execute event - how to pass some external variable, say app user id?
Answering my own question here with a possible solution :)

From http request copied the piece of data to session object
Since the session binding was at engine level, copied the data from session to connection object in SessionEvent.after_begin(session, transaction, connection). [Had it been Connection level binding, we could have directly set the objects from session object to connection object.]

Now the data is available in connection object and in before_execute() too.
I am trying to obtain an application variable (app user id) in before_execute(conn, clauseelement, multiparam, param) method. The app user id is stored in python http request object which I do not have any access to in the db event.
Is there any way to associate a piece of sqlalchemy external data somewhere to fetch it in before_execute event later? 
Appreciate your time and help.