Issue 14972: listcomp with nested classes (original) (raw)
Created on 2012-05-31 21:40 by josmiley, last changed 2022-04-11 14:57 by admin. This issue is now closed.
Messages (5)
Author: josmiley (josmiley)
Date: 2012-05-31 21:40
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())Author: Florent Xicluna (flox) * 
Date: 2012-05-31 21:53
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
Author: Westley MartÃnez (westley.martinez) *
Date: 2012-05-31 22:04
$ 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 "", line 1, in File "", line 3, in A File "", line 3, in 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.
Author: R. David Murray (r.david.murray) *
Date: 2012-05-31 22:07
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.
Author: Florent Xicluna (flox) *
Date: 2012-06-01 15:39
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
History
Date
User
Action
Args
2022-04-11 14:57:31
admin
set
github: 59177
2012-06-01 15:39:55
flox
set
status: open -> closed
superseder: Comprehensions in a class definition mostly cannot access class variable
resolution: duplicate
messages: +
2012-05-31 23:34:03
hynek
set
nosy: + hynek
2012-05-31 22:07:51
r.david.murray
set
nosy: + r.david.murray
messages: +
2012-05-31 22:04:02
westley.martinez
set
nosy: + westley.martinez
messages: +
2012-05-31 22:00:13
alex
set
nosy: + alex
2012-05-31 21:53:08
flox
set
versions: + Python 3.3
nosy: + flox
messages: +
components: + Interpreter Core
2012-05-31 21:40:54
josmiley
create