Fix Python – How to make a cross-module variable?

Question 1

The __debug__ variable is handy in part because it affects every module. If I want to create another variable that works the same way, how would I do it?

The variable (let’s be original and call it ‘foo’) doesn’t have to be truly global, in the sense that if I change foo in one module, it is updated in others. I’d be fine if I could set foo before importing other modules and then they would see the same value for it.

Question 2

I don’t endorse this solution in any way, shape or form. But if you add a variable to the __builtin__ module, it will be accessible as if a global from any other module that includes __builtin__ — which is all of them, by default.

a.py contains

print foo

b.py contains

import __builtin__
__builtin__.foo = 1
import a

The result is that “1” is printed.

Edit: The __builtin__ module is available as the local symbol __builtins__ — that’s the reason for the discrepancy between two of these answers. Also note that __builtin__ has been renamed to builtins in python3.

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