On Mar 20, 3:50 pm, Ian Kelly <ian.g.ke...@gmail.com> wrote:
> On Tue, Mar 20, 2012 at 3:16 PM, Dennis Lee Bieber
>
> <wlfr...@ix.netcom.com> wrote:
> > On Tue, 20 Mar 2012 16:23:22 -0400, "J. Cliff Dyer"
> > <j...@sdf.lonestar.org> declaimed the following in
> > gmane.comp.python.general:
>
> >> When trying to create a class with a dual-loop generator expression in a
> >> class definition, there is a strange scoping issue where the inner
> >> variable is not found, (but the outer loop variable is found), while a
> >> list comprehension has no problem finding both variables.
>
> > Readhttp://www.python.org/dev/peps/pep-0289/-- in particular, look
> > for the word "leak"
>
> No, this has nothing to do with the loop variable leaking. It appears
> to have to do with the fact that the variables and the generator
> expression are inside a class block.
Interesting.
Just for completeness, the code does seem to work fine when you take
it out of the class:
Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more
information.
>>> foo, bar = 4, 4
>>> g = (((x, y), x+y) for x in range(foo) for y in range(bar))
>>> dict(g)
{(0, 1): 1, (1, 2): 3, (3, 2): 5, (0, 0): 0, (3, 3): 6, (3, 0): 3,
(3, 1): 4, (2, 1): 3, (0, 2): 2, (2, 0): 2, (1, 3): 4, (2, 3): 5, (2,
2): 4, (1, 0): 1, (0, 3): 3, (1, 1): 2}
>>> import dis
>>> dis.dis(g.gi_code)
1 0 SETUP_LOOP 57 (to 60)
3 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 50 (to 59)
9 STORE_FAST 1 (x)
12 SETUP_LOOP 41 (to 56)
15 LOAD_GLOBAL 0 (range)
18 LOAD_GLOBAL 1 (bar)
21 CALL_FUNCTION 1
24 GET_ITER
>> 25 FOR_ITER 27 (to 55)
28 STORE_FAST 2 (y)
31 LOAD_FAST 1 (x)
34 LOAD_FAST 2 (y)
37 BUILD_TUPLE 2
40 LOAD_FAST 1 (x)
43 LOAD_FAST 2 (y)
46 BINARY_ADD
47 BUILD_TUPLE 2
50 YIELD_VALUE
51 POP_TOP
52 JUMP_ABSOLUTE 25
>> 55 POP_BLOCK
>> 56 JUMP_ABSOLUTE 6
>> 59 POP_BLOCK
>> 60 LOAD_CONST 0 (None)
63 RETURN_VALUE
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