Python 3: The visibility of global variables across modules

Question

Similar questions have been asked before:

here , here and here , and I am aware of these.

Say you have 2 modules where one has global variables that you want to read from in another module. Is there a way to make these accessible across modules without having to refer to them as module.variable each time?

Example:

modulea.py:

import moduleb
from moduleb import *

print("A String: " + astring)
print("Module B: " + moduleb.astring)
afunction()
print("A String: " + astring)
print("Module B: " + moduleb.astring)

moduleb.py:

astring = "dlroW olleH"

def afunction():
    global astring
    astring = "Hello World"

The output is

A String: dlroW olleH
Module B: dlroW olleH
A String: dlroW olleH
Module B: Hello World

suggesting that by using "from module import * " the global variables are copied rather than referenced.

Thanks in advance for any help.

Answer 1

from module import * binds the objects in module to like named variables in the current module. This is not a copy, but the addition of a reference to the same object. Both modules will see the same object until one of them rebinds the object. Modifying a mutable object doesn't rebind the variable so an action such as appending to a list is okay. But reassigning the the variable does rebind it. Usually the rebind is straight forward:

myvar = something_else

But sometimes its not so clear

myvar += 1

For immutable objects such as int or str , this rebinds the variable and now the two modules have different values.

If you want to make sure you always reference the same object, keep the namespace reference.