Re: Python: exec in a function can't create shadows of variables if these are declared "global" in another function of the same module

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Thu, Nov 13, 2008 at 02:50:17PM +0000, Silas S. Brown wrote:
>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

Observed on:

Python 2.5.2 on 2.6.26-gentoo-r1 (i.e., linux)

So this isn't just a Cygwin-specific behavior.  It probably would be best
to take this to a python mailing list.

I agree that it does seem like strange behavior, though.

cgf

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