[Python-ideas] Deterministic iterator cleanup

[Oscar Benjamin]

On 19 October 2016 at 12:33, Oscar Benjamin <oscar.j.benjamin at gmail.com> wrote:
>
>> New convenience functions
>> -------------------------
>>
>> The ``itertools`` module gains a new iterator wrapper that can be used
>> to selectively disable the new ``__iterclose__`` behavior::
>>
>>   # XX FIXME: I feel like there might be a better name for this one?
>>   class protect(iterable):
>>       def __init__(self, iterable):
>>           self._it = iter(iterable)
>>
>>       def __iter__(self):
>>           return self
>>
>>       def __next__(self):
>>           return next(self._it)
>>
>>       def __iterclose__(self):
>>           # Swallow __iterclose__ without passing it on
>>           pass
>>
>> Example usage (assuming that file objects implements ``__iterclose__``)::
>>
>>   with open(...) as handle:
>>       # Iterate through the same file twice:
>>       for line in itertools.protect(handle):
>>           ...
>>       handle.seek(0)
>>       for line in itertools.protect(handle):
>>           ...
>
> It would be much simpler to reverse this suggestion and say let's
> introduce a helper that selectively *enables* the new behaviour you're
> proposing i.e.:
>
> for line in itertools.closeafter(open(...)):
>     ...
>     if not line.startswith('#'):
>         break  # <--------------- file gets closed here

Looking more closely at this I realise that there is no way to
implement closeafter like this without depending on closeafter.__del__
to do the closing. So actually this is not a solution to the problem
at all. Sorry for the noise there!

-- 
Oscar