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Python: exec in a function can't create shadows of variables if these are declared "global" in another function of the same module
- From: "Silas S. Brown" <ssb22 at cam dot ac dot uk>
- To: cygwin at cygwin dot com
- Date: Thu, 13 Nov 2008 14:50:17 +0000
- Subject: Python: exec in a function can't create shadows of variables if these are declared "global" in another function of the same module
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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