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Date:	Thu, 13 Nov 2008 14:50:17 +0000
From:	"Silas S. Brown" <ssb22 AT cam DOT ac DOT uk>
To:	cygwin AT cygwin DOT com
Subject:	Python: exec in a function can't create shadows of variables if these are declared "global" in another function of the same module
Message-ID:	<20081113145017.GA32353@smaug.linux.pwf.cam.ac.uk>
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Consider this Python code:

setting1 = "val1"
setting2 = "val2"

def dummy():
    global setting1

def f(x):
    exec(x)
    return setting1, setting2

print f("setting1='new' ; setting2='new'")

Expected result: ('new', 'new')

Actual result: ('val1', 'new')

The presence of "global setting1" in a totally
different function somehow stops a shadowed
setting1 from being created by the exec.

This can be worked around by adding a real
assignment before the exec, i.e.:

def f(x):
    setting1 = 0
    exec(x)
    return setting1, setting2

Observed in:
Python 2.5.1 (r251:54863, May 18 2007, 16:56:43) on Cygwin

Not observed in:
Python 2.5.1 (r251:54863, Aug  1 2008, 00:32:16) on SUSE Linux

Silas


-- 
Silas S Brown http://people.pwf.cam.ac.uk/ssb22

"If your axe is dull and you don't sharpen it,
 you have to work harder to use it." - Ecclesiastes 10:10 (TEV)

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