Question

I am looking for a way to correctly manage module level global variables that use some operating system resource (like a file or a thread).

The problem is that when the module is reloaded, my resource must be properly disposed (e.g. the file closed or the thread terminated) before creating the new one.

So I need a better pattern to manage those singleton objects.

Answer 1

I’ve been reading the docs on module reload and this is quite interesting:

When a module is reloaded, its dictionary (containing the module’s
global variables) is retained. Redefinitions of names will override
the old definitions, so this is generally not a problem. If the new
version of a module does not define a name that was defined by the old
version, the old definition remains. This feature can be used to the
module’s advantage if it maintains a global table or cache of objects
— with a try statement it can test for the table’s presence and skip
its initialization if desired:

try:
    cache
except NameError:
    cache = {}

So I could just check if the objects already exist, and dispose them before creating the new ones.