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# this runs with python2.7, not with python3.2
class Foo(object):
 class Bar(object):
 pass
 Attr = [Bar()for n in range(10)]
# solved in this way ...
class Foo(object):
 class Bar(object):
 pass
 Attr = []
 for n in range(10): Attr.append(Bar())

Simpler test case:
class A:
 x = 42
 y = [x for _ in '1']
The semantics of list comprehension changed with Python 3.
However, I do not see this specific behavior documented somewhere.
http://docs.python.org/dev/whatsnew/3.0.html#changed-syntax 

$ python
Python 3.2.3 (default, Apr 23 2012, 23:35:30) 
[GCC 4.7.0 20120414 (prerelease)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class A:
... x = 42
... y = [x for _ in '1']
... 
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "<stdin>", line 3, in A
 File "<stdin>", line 3, in <listcomp>
NameError: global name 'x' is not defined
>>> x = 42
>>> class A:
... x = 12
... y = [x for _ in '1']
... 
>>> A.y
[42]
It seems that the list comprehension is looking at the module's scope as opposed to the class scope. This definitely seems incorrect to me.

This is doubtless a result of the way the class namespace scope is handled, coupled with the fact that in Python3 list comprehensions have a local scope. The class scope is a somewhat unique beast. I agree that this is unfortunate, but I have a feeling that doing anything about it is distinctly non-trivial.

This is a duplicate of issue 11796.
See also issue 13557:
http://bugs.python.org/issue13557#msg154174
For Python 3, a list comprehension defines a block pretty much like the method definition during the class creation:
class x:
 x = 1
 def incx():
 return x + 1
 print(incx())
 ==> raises NameError too