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Question About When Objects Are Destroyed (continued)


On Sun, Aug 6, 2017 at 1:23 AM, Tim Daneliuk <info at tundraware.com> wrote:
> On 08/04/2017 07:00 PM, Chris Angelico wrote:
>> Again, don't stress about exactly when objects get
>> disposed of; it doesn't matter.
>
>
> Respectfully, I disagree strongly.  Objects get build on the heap and
> persist even when they go out of scope until such time garbage
> collection takes place.  This is unlike languages that build things in
> stack frames which naturally disappear with an exit of scope.
>
> For small or trivial programs, it does not matter.  But when there is a
> lot of dynamic object construction - say, in very large programs, object
> factories, etc. - it can be important to harvest the space of expired
> objects sooner, rather than later.  This, after all, is one of the
> rationale' for Python contexts - to ensure the release of resources no
> matter how the logic ends - correctly or by exception.

By "contexts", you're presumably talking about the way you can use a
'with' block to guarantee resource release. But that is actually
orthogonal to object destruction; in fact, it's specifically because
the object might NOT be destroyed at that point. Before that feature
was implemented, people depended on CPython's reference counting and
consequent object destruction (and __del__) to close files and other
resources. That doesn't work reliably in all Python implementations,
though, so a more dependable system was needed. After a 'with' block,
the object *still exists*, but it has been "exited" in some way
(usually by closing/releasing an underlying resource).

So, again, you must not concern yourself with when the objects
themselves get destroyed. If there's a resource you need to clean up,
you clean that up explicitly, so the object's lifetime shouldn't
matter to you.

ChrisA