Using `if session` to only run code when session has initialised fails about py-shiny HOT 2 CLOSED

It looks like that error message needs to be fixed.

An explanation of what's happening:

• With Shiny Express apps, the code in the .py file is run once at startup to generate the UI (which is saved and served each time someone connects), and once for each new user session.
• For the first, UI-generating pass, the shiny.express.session is not a real Session object, but instead a ExpressMockSession object. This is the object which throws errors when you try to access the .id member.
• For the user sessions, shiny.express.session is a Sesssion object, and accessing members of it will work fine.

I think it would make sense to add a method to ExpressMockSession and Session, which reports whether it is a real session object.

For the moment your workaround should be OK. Or you can use this, which is slightly less hacky:

from shiny.session import Session
from shiny.express import session

if isinstance(session, Session):
    print("The session ID is:" + str(session.id))

from py-shiny.

In #1331, we added a new method .is_stub_session(). So with the development version of shiny, you should be able to do:

from shiny.express import session

if not session.is_stub_session():
    print("The session ID is:" + str(session.id))

from py-shiny.