[Python-Dev] issue5578 - explanation

[Jeremy Hylton]

I posted in the bug report, but repeating here:  I don't remember why
exec in a nested function changed either.  It would help if someone
could summarize why we made the change.  (I hope I didn't do it <0.2
wink>.)

Jeremy

On Tue, Mar 31, 2009 at 11:36 PM, Maciej Fijalkowski <fijall at gmail.com> wrote:
> Because classes have now it's own local scope (according to Martin)
>
> It's not about exec in class, it's about exec in class in nested function.
>
> On Wed, Apr 1, 2009 at 5:25 AM, Guido van Rossum <guido at python.org> wrote:
>> Well hold on for a minute, I remember we used to have an exec
>> statement in a class body in the standard library, to define some file
>> methods in socket.py IIRC.  It's a totally different case than exec in
>> a nested function, and I don't believe it should be turned into a
>> syntax error at all. An exec in a class body is probably meant to
>> define some methods or other class attributes. I actually think the
>> 2.5 behavior is correct, and I don't know why it changed in 2.6.
>>
>> --Guido
>>
>> On Tue, Mar 31, 2009 at 8:15 PM, Maciej Fijalkowski <fijall at gmail.com> wrote:
>>> So. The issue was closed and I suppose it was closed by not entirely
>>> understanding
>>> the problem (or I didn't get it completely).
>>>
>>> The question is - what the following code should do?
>>>
>>> def f():
>>>  a = 2
>>>  class C:
>>>    exec 'a = 42'
>>>    abc = a
>>>  return C
>>>
>>> print f().abc
>>>
>>> (quick answer - on python2.5 it return 42, on python 2.6 and up it
>>> returns 2, the patch changes
>>> it to syntax error).
>>>
>>> I would say that returning 2 is the less obvious thing to do. The
>>> reason why IMO this should
>>> be a syntax error is this code:
>>>
>>> def f():
>>>  a = 2
>>>  def g():
>>>    exec 'a = 42'
>>>    abc = a
>>>
>>> which throws syntax error.
>>>
>>> Cheers,
>>> fijal
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>>
>>
>>
>> --
>> --Guido van Rossum (home page: http://www.python.org/~guido/)
>>
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