Is this a bug, or is it me?

[Hrvoje Niksic]

"Neil Cerutti" <mr.cerutti at gmail.com> writes:

> You cannot access a class's class variables in it's class-statement
> scope, since the name of the type is not bound until after the class
> statement is completed.

But they are still available as locals, so you can access them using
their names, like this:

>>> class C:
...   a = 1
...   b = 2
...   print a+b
...
3

The question is, why doesn't the OP's code snippet work?  It seems
that the generator expression can't read the surrounding locals().
But when you change the generator expression to a list comprehension
using a pair of [] around it, it starts working.  Compare:

class C(object):
    d = {}
    for a in 1, 2, 3:
        ignore = list((a, b) for b in (4, 5, 6))

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in C
  File "<stdin>", line 4, in <genexpr>
NameError: global name 'a' is not defined

with:

class C(object):
    d = {}
    for a in 1, 2, 3:
        ignore = [(a, b) for b in (4, 5, 6)]

It seems that generator expressions and list comprehensions have
subtly different scoping rules.  Whether this is a bug or not is a
good question.