On Fri, Oct 21, 2016 at 3:48 PM, Amit Green <amit.mi...@gmail.com> wrote:
> NOTE: This is my first post to this mailing list, I'm not really sure
> how to post a message, so I'm attempting a reply-all.
>
> I like Nathaniel's idea for __iterclose__.
>
> I suggest the following changes to deal with a few of the complex issues
> he discussed.
>
> 1. Missing __iterclose__, or a value of none, works as before,
> no changes.
>
> 2. An iterator can be used in one of three ways:
>
> A. 'for' loop, which will call __iterclose__ when it exits
>
> B. User controlled, in which case the user is responsible to use the
> iterator inside a with statement.
>
> C. Old style. The user is responsible for calling __iterclose__
>
> 3. An iterator keeps track of __iter__ calls, this allows it to know
> when to cleanup.
>
>
> The two key additions, above, are:
>
> #2B. User can use iterator with __enter__ & __exit cleanly.
>
> #3. By tracking __iter__ calls, it makes complex user cases easier
> to handle.
These are interesting ideas! A few general comments:
- I don't think we want the "don't bother to call __iterclose__ on
exhaustion" functionality --it's actually useful to be able to
distinguish between
# closes file_handle
for line in file_handle:
...
and
# leaves file_handle open
for line in preserve(file_handle):
...
To be able to distinguish these cases, it's important that the 'for'
loop always call __iterclose__ (which preserve() might then cancel
out).
- I think it'd be practically difficult and maybe too much magic to
add __enter__/__exit__/nesting-depth counts to every iterator
implementation. But, the idea of using a context manager for repeated
partial iteration is a great idea :-). How's this for a simplified
version that still covers the main use cases?
@contextmanager
def reuse_then_close(it): # TODO: come up with a better name
it = iter(it)
try:
yield preserve(it)
finally:
iterclose(it)
with itertools.reuse_then_close(some_generator(...)) as it:
for obj in it:
...
# still open here, because our reference to the iterator is
wrapped in preserve(...)
for obj in it:
...
# but then closed here, by the 'with' block
-n
--
Nathaniel J. Smith -- https://vorpus.org
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