Dynamically declared shared constant/variable imported twice problem

  • Thread starter Gabriel Rossetti
  • Start date

G

Gabriel Rossetti

Hello everyone,

I have three modules A, B, C;

A declares this globally :

UpdateEvent, UPDATE_EVENT_ID = wx.lib.newevent.NewEvent()

Then they import stuff from each other:

- A imports a constant from module B (in "__main__")
- A imports a class and some constants from module C
- B imports a constant from module A
- C imports UPDATE_EVENT_ID from module A

What happens is that since A imports stuff from B which then in turn
loads something from A, UPDATE_EVENT_ID gets redefined and when A sends
an event to C, C doesn't do anything since it doesn't have the same
UPDATE_EVENT_ID. Does anyone have an idea on how to fix this? If it had
been a statically defined variable then that wouldn't be "bad", but
since it's dynamic it does pose problems. More globally, how cn I
prevent this even with static constants? I don't think it's that great
to redefine the stuff multiple times and I've already had this problem
in the past with a constant dict.

Thank you,
Gabriel
 
Ad

Advertisements

P

Peter Otten

Gabriel said:
I have three modules A, B, C;

A declares this globally :

UpdateEvent, UPDATE_EVENT_ID = wx.lib.newevent.NewEvent()

Then they import stuff from each other:

- A imports a constant from module B (in "__main__")
- A imports a class and some constants from module C
- B imports a constant from module A
- C imports UPDATE_EVENT_ID from module A

What happens is that since A imports stuff from B which then in turn
loads something from A, UPDATE_EVENT_ID gets redefined and when A sends
an event to C, C doesn't do anything since it doesn't have the same
UPDATE_EVENT_ID. Does anyone have an idea on how to fix this? If it had
been a statically defined variable then that wouldn't be "bad", but
since it's dynamic it does pose problems. More globally, how cn I
prevent this even with static constants? I don't think it's that great
to redefine the stuff multiple times and I've already had this problem
in the past with a constant dict.

Imported modules are cached, so this problem shouldn't occur unless you use
A.py as your main script. In this case it will be cached as "__main__", and
if you import it elsewhere a second copy will be executed and cached as "A".

To fix it create a wrapper script that doesn't create any objects that will
be used elsewhere, e. g.

#!/usr/bin/env python
import A
A.main()

assuming the function A.main() contains the code to start your application
and invoke that instead of A.py

Peter
 
Ad

Advertisements

G

Gabriel Rossetti

Peter said:
Gabriel Rossetti wrote:



Imported modules are cached, so this problem shouldn't occur unless you use
A.py as your main script. In this case it will be cached as "__main__", and
if you import it elsewhere a second copy will be executed and cached as "A".

To fix it create a wrapper script that doesn't create any objects that will
be used elsewhere, e. g.

#!/usr/bin/env python
import A
A.main()

assuming the function A.main() contains the code to start your application
and invoke that instead of A.py

Peter
Thank you Peter, I understand better now. I am indeed using A.py as my
main script. I will create a launcher then, thank you.

Gabriel
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Top