generator expression works in shell, NameError in script

Bruno Desthuilliers bruno.42.desthuilliers at websiteburo.invalid
Fri Jun 19 14:45:43 CEST 2009


Emile van Sebille a écrit :
> On 6/17/2009 3:54 PM ssc said...
>> Wow! Didn't expect that kind of instant support. Thank you very much,
>> I'll give both zip and enumerate a try.
>>
>> The code I've shown is actually copied pretty straight from a Django
>> form class, but I didn't want to mention that as not to dilute the
>> conversation. Don't think it matters, anyway. This is the relevant
>> excerpt:
>>
>> from django.forms import Form
>>
>> class SignupForm(Form):
>>
>>     titles = ['Dr', 'Miss', 'Mr', 'Mrs', 'Ms',]
>>     title_choices   = [(0, '')] + list((titles.index(t)+1, t) for t in
>> titles)
>>
>> Now that I look at it again, it seems odd to me to not have the code
>> e.g. in __init__(...), but just 'class-global'.
> 
> And as class is an executable statement, I imagine titles exists in a 
> namespace that hasn't yet been completely defined.

>> Still, that does not seem a reason for titles not to be not defined,
>> as I do define it just in the line above.
> 
> Well, again, titles will exists in the SignupForm namespace once it 
> exists, which it doesn't yet when you get to title_choices and want to 
> access it. 

The namespace itself is as defined at any point of the class statement's 
body as the local namespace of a function at any given point of the 
function's body. Else decorators (or their alternate pre '@' 
syntactic-sugar version) wouldn't work.


FWIW, the following code works JustFine(tm):

bruno at bruno:~$ python
Python 2.5.2 (r252:60911, Oct  5 2008, 19:24:49)
[GCC 4.3.2] on linux2
 >>> class Foo(object):
...     bar = ['a', 'b', 'c']
...     baaz = list(enumerate(bar))

as well as this one:

 >>> class Foo(object):
...     bar = ['a', 'b', 'c']
...     baaz = [(bar.index(t)+1, t) for t in bar]

and this one:

 >>> class Foo(object):
...     bar = ['a', 'b', 'c']
...     baaz = list((b, b) for b in bar)



but it indeed looks like using bar.index *in a generator expression* 
fails (at least in 2.5.2) :

  >>> class Foo(object):
...     bar = ['a', 'b', 'c']
...     baaz = list((bar.index(b), b) for b in bar)
...
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "<stdin>", line 3, in Foo
   File "<stdin>", line 3, in <genexpr>
NameError: global name 'bar' is not defined


Looks like a bug to me :-/




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