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Change in behaviour Python 3.7 > 3.8


06.02.20 14:58, Frank Millman ????:
> I have noticed a change in behaviour in Python 3.8 compared with 
> previous versions of Python going back to at least 2.7. I am pretty sure 
> that it is not a problem, and is caused by my relying on a certain 
> sequence of events at shutdown, which of course is not guaranteed. 
> However, any change in behaviour is worth reporting, just in case it was 
> unintended, so I thought I would mention it here.
> 
> I have a module (A) containing common objects shared by other modules. I 
> have a module (B) which imports one of these common objects - a set().
> 
> Module B defines a Class, and creates a global instance of this class 
> when the module is created. This instance is never explicitly deleted, 
> so I assume it gets implicitly deleted at shutdown. It has a __del__() 
> method (only for temporary debugging purposes, so will be removed for 
> production) and the __del__ method uses the set() object imported from 
> Module A.
> 
> This has worked for years, but now when the __del__ method is called, 
> the common object, which was a set(), has become None.
> 
> My assumption is that Module A gets cleaned up before Module B, and when 
> Module B tries to access the common set() object it no longer exists.

Do you import a common object *from* a module or import a module and 
access a common object as its attribute?

If the latter, the change may be related to
https://bugs.python.org/issue33331 . Modules are now cleaned up in the 
reversed order of importing.

In any case, the order of cleaning up modules is not specified/