Questions on variable changing between files.

[nilamo]

# This is File A
from fileb import bvar

bvar = 10

There seem to be a lot of assumptions that you want to save that value to the original file, so the next time you open up fileb, it'd be 10 instead of whatever it used to be.  I'm not sure that's what you're asking.  If you just want to change it while it's running, sort of like a config value, then work with the file as a module directly, instead of only importing the single variable.  Like so:

#file a
import fileb

print(fileb.bvar) # 5, maybe

fileb.bvar = 10

print(fileb.bvar) # 10 here, and also 10 for anything in fileb that uses it

Although you'd need a pretty good reason to want to do that, since it could easily make reading fileb and understanding why the output is as it is fairly complicated.