[Python-Dev] Preserving the blamelist

[Tim Peters]

[Neal]
>> ...
>> I'm concerned about the negative ref leak in test_contextlib.  I
>> wonder if this was a result of PJE's fix for generators?

[Tim]
> I don't know, but if you do
>
> while 1:
>     test_contextlib.test_main()
>     gc.collect()
>
> under a debug build it eventually (> 500 iterations) crashes with
>
>     Fatal Python error: deallocating None
> ...

OK, I fixed that (incorrect decref in gen_throw()).

Neal, that should also repair test_contextlib's ref leak oddities. 
The reason you didn't see this before is that test_contextlib didn't
actually run any tests until recently.

Phillip, when eyeballing gen_dealloc(), I didn't understand two things:

1. Why doesn't

	if (gen->gi_frame->f_stacktop!=NULL) {

   check first to be sure that gen->gi_frame != Py_None?  Is that impossible
   here for some reason?

2. It _looks_ like "gi_frame != NULL" is an (undocumented) invariant. 
Right?  If so,

	Py_XDECREF(gen->gi_frame);

   sends a confusing message (because of the "X", implying that NULL is OK).
   Regardless, it would be good to add comments to genobject.h explaining
   the possible values gi_frame can hold.  For example, what does it mean
   when gi_frame is Py_None?  Can it ever be NULL?  It's very hard to reverse-
   engineer invariants and "special value" intents from staring at code.  Not to
   say that isn't fun ;-)