Problem with global variables

[Marc 'BlackJack' Rintsch]

On Fri, 08 Aug 2008 13:10:48 -0400, Anthony Kuhlman wrote:

> I'm having trouble understanding the behavior of global variables in a
> code I'm writing.  I have a file, test.py, with the following contents
> 
> foo = []
> 
> def goo():
>     global foo
>     foo = []
>     foo.append(2)
> 
> def moo():
>     print foo
> 
> In an ipython session, I see the following:
> 
> In [1]: from test import *
> 
> In [2]: foo
> Out[2]: []
> 
> In [3]: goo()
> 
> In [4]: foo
> Out[4]: []
> 
> In [5]: moo()
> [2]
> 
> I don't understand this behavior.  I assumed that foo as defined in
> test.py is a global object, but that doesn't seem to be the case.

``global`` means module global.  There's no really global namespace in 
Python.

> The ipython session seems to be dealing with one copy of foo while
> goo() and moo() are using an entirely different copy.

The import binds the list from the module to the name `foo` in the 
IPython namespace.  When you call `goo()` it binds the name `foo` *within 
the module* to a new list.  This has of course no influence on the name 
in the IPython namespace which is still bound to the list object that was 
bound to `test.foo` before.

Ciao,
	Marc 'BlackJack' Rintsch