Global variables in modules/functions

[Aaron Deskins]

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
change.py, but this only gives an error message.

Any ideas?

Thanks


--
Aaron Deskins
Graduate Student
Chemical Engineering
Purdue University

[Michel Claveau - abstraction méta-galactique non t]

Re: Global variables in modules/functions

Hi !

It is extraordinary: I have just had the same problem, there is seulemet
one hour!
For the moment, I prefix the variable; but I will read with interest the
reponses with your message.

@-salutations
--
Michel Claveau

[Peter Otten]

Re: Global variables in modules/functions

Aaron Deskins wrote:
[color=blue]
> 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[/color]

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.
[color=blue]
> change.py, but this only gives an error message.
>
> Any ideas?[/color]

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

[Peter Otten]

Re: Global variables in modules/functions

Peter Otten wrote:
[color=blue]
> 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[/color]

Oops, that should be

print shared.n
[color=blue]
> change.py
> import shared
> def change_n():
> shared.n = 2
>[/color]

[Erik Max Francis]

Re: Global variables in modules/functions

Aaron Deskins wrote:
[color=blue]
> 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.[/color]

Globals aren't common to all modules. You can think of globals as
module-specific. That is, the global n is not shared between your two
modules. It will be in one of the modules, and the other module can
then reference it explicitly. Something like (untested):

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

change.py
---------
n = 0 # here's the actual global
def change_n():
global n
n = 2

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
They have rights who dare defend them.
-- Roger Baldwin

[Scott David Daniels]

Re: Global variables in modules/functions

Aaron Deskins wrote:[color=blue]
> 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.[/color]
The easiest way to do this is to create a module named "globals", and
have any modules wanting to work like:

import globals
....
def change_n():
globals.n = 2

Here's an example.
____________
main.py
____________
import globals, change
globals.n = 1
change.change_n ()
print globals.n
____________
change.py
____________
import globals
def change_n():
globals.n = 2

There are ways to force python into doing what you want, but they are
fraught with peril.

--Scott David Daniels
Scott.Daniels@A cm.Org

[Jeff Shannon]

Re: Global variables in modules/functions

Scott David Daniels wrote:
[color=blue]
> The easiest way to do this is to create a module named "globals", and
> have any modules wanting to work like:[/color]


.... except that you might want to use a different name, to avoid
shadowing the globals() builtin function. :)

Jeff Shannon
Technician/Programmer
Credit International

[Aaron Deskins]

Re: Global variables in modules/functions

Thanks! That works great.

Scott David Daniels wrote:
[color=blue]
>
> The easiest way to do this is to create a module named "globals", and
> have any modules wanting to work like:
>
> import globals
> ...
> def change_n():
> globals.n = 2
>[/color]