Global Variables - Unable to access Global vars outside of Module

Anvil Q&A
1

What I’m trying to do:
I have a global variable defined in my main module containing user info. I would like to be able to use this variable outside of the module in my actual forms.

My startup Module, MainModule, is set up like so:

def main():
  global user
  # check if a user is logged in
  user_logged_in = anvil.server.call("check_user_login_status")
  if user_logged_in:
    user = user_logged_in 
    open_form("MainRouter")
  else:
    # Redirect user to login template:
    user = None
    open_form("FormLandingPage")
    

if __name__ == "__main__":
  main()

What I’ve tried and what’s not working:
I would like to be able to use the global variable ‘user’ in my MainRouter form,
but when I import MainModule ( from … import MainModule) into MainRouter, I get the following error:

AttributeError: module 'MyApp.MainModule' has no attribute 'user'

** Some other potentially relavent details**

  • MainModule is my startup form
  • MainRouter uses HashRouting and has the decorator ‘@routing.main_router’

Please let me know if there are any other details I can supply. Based on what I’ve read on other forms (and in anvil-extras docs here: Routing — Anvil Extras documentation) it seems like what I am trying to do should work… Thanks!

2

Seeing the line that raises the error would help.

Perhaps all you need is to add user = None outside of the main function, so the variable user is defined in the module rather than used as a global reference inside a function.

3

image
image816×617 85.2 KB

(wrt the image, MainModule line 34 is open_form(“MainRouter”))

I have tried setting user = None outside of the main function, this prevents the error but causes the global var user to have the value None in all forms
aka:

# In MainRouter
from .. import MainModule

print(MainModule.user) # prints "None"
4

It’s None because that’s what you assigned to it.

I don’t understand why you have a function called main and this code.

The function main is never executed here, so the value of user remains None.

5

I wouldn’t rely on global variables that only exist in your startup module.

That’s because your startup module is initially executed with __name__ "__main__" but when it is subsequently imported to another form it is re-executed with __name__ "MainModule". If you print __name__ in the module scope you’ll see this gets executed twice.

Better to put user into a Globals module and import the Globals module into both the startup module and the main form. Then access it like Globals.user

1 Like
6

Nice. Thanks for the quick help, This worked. Very much appreciated

best,

1 Like