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From: Ned Batchelder <ned@nedbatchelder.com>
Subject: Re: Why this throws an UnboundLocalError ?
Date: Thu, 30 Jan 2014 17:56:17 -0500
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On 1/30/14 5:46 PM, Marc Aymerich wrote:
> Dear all,
>
> I have a very simple module
>
> glic3@e4200:# cat globalstate.py
> GLOBAL = 0
>
> def update():
>      GLOBAL += 1
>
>
> however it doesn't work!!
>
> glic3@e4200:# python
> Python 2.7.3 (default, Aug  1 2012, 05:14:39)
> [GCC 4.6.3] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> import globalstate
>>>> globalstate.update()
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
>    File "globalstate.py", line 4, in update
>      GLOBAL += 1
> UnboundLocalError: local variable 'GLOBAL' referenced before assignment
>
>
> And I don't know why :(
> Anyone ?
>
> Thanks!!
>

Assignment statements in functions implicitly make local names. If you 
want to assign a new value to a global name in a function, you have to 
use a global statement:

def update():
     global GLOBAL
     GLOBAL += 1

-- 
Ned Batchelder, http://nedbatchelder.com