[Python-ideas] Deterministic iterator cleanup

[Yury Selivanov]

On 2016-10-21 6:29 AM, Steven D'Aprano wrote:
> On Wed, Oct 19, 2016 at 05:52:34PM -0400, Yury Selivanov wrote:
[..]
>> With you proposal, to achieve the same (and make the code compatible
>> with new for-loop semantics), users will have to implement both
>> __iterclose__ and __del__.
> As I ask above, couldn't we just inherit a default __(a)iterclose__ from
> object that looks like this?
>
>      def __iterclose__(self):
>          finalizer = getattr(type(self), '__del__', None)
>          if finalizer:
>              finalizer(self)
>
>
> I know it looks a bit funny for non-iterables to have an iterclose
> method, but they'll never actually be called.

No, we can't call __del__ from __iterclose__.  Otherwise we'd
break even more code that this proposal already breaks:


   for i in iter:
      ...
   iter.something()  # <- this would be call after iter.__del__()

[..]
> As for the amount of good, this proposal originally came from PyPy. I
> expect that CPython users won't appreciate it as much as PyPy users, and
> Jython/IronPython users when they eventually support Python 3.x.

AFAIK the proposal came "for" PyPy, not "from".  And the
issues Nathaniel tries to solve do also exist in CPython.  It's
only a question if changing 'for' statement and iteration protocol
is worth the trouble.

Yury