RFC: Proposal: Deterministic Object Destruction

[Ian Kelly]

On Thu, Mar 1, 2018 at 10:35 PM, Chris Angelico <rosuav at gmail.com> wrote:
> On Fri, Mar 2, 2018 at 4:16 PM, Ian Kelly <ian.g.kelly at gmail.com> wrote:
>> On Wed, Feb 28, 2018 at 8:00 PM, Chris Angelico <rosuav at gmail.com> wrote:
>>> Not off hand, but I can provide an EXTREMELY real-world example of a
>>> fairly tight loop: exceptions. An exception has a reference to the
>>> local variables it came from, and those locals may well include the
>>> exception itself:
>>>
>>> try:
>>>     1/0
>>> except Exception as e:
>>>     print(e)
>>>
>>> The ZeroDivisionError has a reference to the locals, and 'e' in the
>>> locals refers to that very exception object.
>>
>> The problem with this example of course is that the variable 'e' is
>> scoped to the except block and automatically del'ed when it exits.
>
> Or, to be more accurate: The language design acknowledges that this
> reference cycle is a fundamental problem, and the *solution* is that
> there's an implicit "e = None; del e" at the end of the except block.
>
> You can easily defeat that protection with "except Exception as ee: e
> = ee", if you want to demonstrate the cycle.

Yes, but how often does this happen in practice? This situation was
billed as "an EXTREMELY real-world example". In the real world, most
of the time when you have an exception, you log it or handle it, and
then you discard it.