Global variables in modules/functions

[Peter Otten]

Aaron Deskins wrote:

> I'm trying to write program with a main.py and several functions
> distributed in auxiliary *.py files. I've looked through the archives on
> the 'global' keyword, but I'm still not sure how to get this right. I
> want to be able to have some variables that can be accessed/changed by
> many modules/functions.
> 
> Here's an example.
> 
> ____________
> main.py
> ____________
> import change
> n = 1
> change.change_n()
> print n
> 
> ____________
> change.py
> ____________
> def change_n():
>      global n
>      n = 2
> 
> 
> Running main.py gives this: 1. So n is not being changed when the
> function is called. I've tried adding a 'import from main *' line to

The correct syntax is

from main import *

This will only copy the binding
n = 1
and a following 
n = 2 
assignment will not affect n in the main module.

> change.py, but this only gives an error message.
> 
> Any ideas?

A clean way to share data between different modules is to introduce another
module and use a qualified name to access data in that module:

shared.py
n = 1

main.py
import shared
import change

change.change_n()
print n

change.py
import shared
def change_n():
    shared.n = 2


However, I'm not convinced that you really need that kind of global data at
all:

main.py
import change
n = 1
n = change.change_n()
print n

change.py
def change_n():
   return 2

is clearly a superior design.

Finally, what you originally requested is not impossible, just bad:

change.py
import sys

def change_n():
    sys._getframe(1).f_globals["n"] = 2

Peter