[Python-ideas] Membership of infinite iterators

Koos Zevenhoven k7hoven at gmail.com
Wed Oct 18 08:36:15 EDT 2017

On Wed, Oct 18, 2017 at 2:08 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 18 October 2017 at 20:39, Koos Zevenhoven <k7hoven at gmail.com> wrote:
>> On Oct 18, 2017 13:29, "Nick Coghlan" <ncoghlan at gmail.com> wrote:
>> On 18 October 2017 at 19:56, Koos Zevenhoven <k7hoven at gmail.com> wrote:
>>> I'm unable to reproduce the "uninterruptible with Ctrl-C"​ problem with
>>> infinite iterators. At least itertools doesn't seem to have it:
>>> >>> import itertools
>>> >>> for i in itertools.count():
>>> ...     pass
>>> ...
>> That's interrupting the for loop, not the iterator. This is the test case
>> you want for the problem Jason raised:
>>     >>> "a" in itertools.count()
>> Be prepared to suspend and terminate the affected process, because Ctrl-C
>> isn't going to help :)
>> I'm writing from my phone now, cause I was dumb enough to try
>> list(count())
> Yeah, that's pretty much the worst case example, since the machine starts
> thrashing memory long before it actually gives up and starts denying the
> allocation requests :(
>> But should it be fixed in list or in count?
> That one can only be fixed in count() - list already checks
> operator.length_hint(), so implementing itertools.count.__length_hint__()
> to always raise an exception would be enough to handle the container
> constructor case.
While that may be a convenient hack to solve some of the cases, maybe it's
possible for list(..) etc. to give Ctrl-C a chance every now and then?
(Without a noticeable performance penalty, that is.) That would also help
with *finite* C-implemented iterables that are just slow to turn into a

If I'm not mistaken, we're talking about C-implemented functions that
iterate over C-implemented iterators. It's not at all obvious to me that
it's the iterator that should handle Ctrl-C.


+ Koos Zevenhoven + http://twitter.com/k7hoven +
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