[Python-Dev] variable name resolution in exec is incorrect

Michael Foord fuzzyman at voidspace.org.uk
Wed May 26 15:08:35 CEST 2010


On 26/05/2010 13:51, Nick Coghlan wrote:
> On 26/05/10 19:48, Mark Dickinson wrote:
>> This is a long way from my area of expertise (I'm commenting here
>> because it was me who sent Colin here in the first place), and it's
>> not clear to me whether this is a bug, and if it is a bug, how it
>> could be resolved. What would the impact be of having the compiler
>> produce 'LOAD_NAME' rather than 'LOAD_GLOBAL' here?
>
> exec with a single argument = module namespace
> exec with two arguments = class namespace
>
> Class namespaces are deliberately exempted from lexical scoping so 
> that methods can't see class attributes, hence the example in the 
> tracker issue works exactly as it would if the code was written as a 
> class body.
>
> class C:
> y = 3
> def execfunc():
> print y
> execfunc()
>
> With this code, y would end up in C.__dict__ rather than the module 
> globals (at least, it would if it wasn't for the exception) and the 
> call to execfunc fails with a NameError when attempting to find y.
>
> I know I've closed other bug reports that were based on the same 
> misunderstanding, and I didn't understand it myself until Guido 
> explained it to me a few years back, so suggestions for improving the 
> exec documentation in this area would be appreciated.

Your explanation here is very clear. Is this in the documentation?

Michael

>
> Cheers,
> Nick.
>


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