Question About When Objects Are Destroyed (continued)

Sat Aug 5 20:14:42 EDT 2017

On 08/05/2017 05:36 PM, Ned Batchelder wrote:
> On 8/5/17 5:41 PM, Tim Daneliuk wrote:
>> On 08/05/2017 11:16 AM, Ned Batchelder wrote:
>>> It uses
>>> reference counting, so most objects are reclaimed immediately when their
>>> reference count goes to zero, such as at the end of local scopes. 
>> Given this code:
>>>> class SomeObject:
>> .....
>>>>>> for foo in somelist:
>>>> a = SomeObject(foo)
>> b = SomeObject(foo)
>> c = SomeObject(foo)
>>>> # Do something or other
>> ...
>>>> # Bottom of 'for' scope
>>>>>> Are you saying that each time a,b,c are reassigned to new instances of
>> SomeObject the old instance counts go to 0 and are immediately - as in
>> synchronously, right now, on the spot - removed from memory? 
> Yes, that is what I am saying. In CPython, that is. Other
> implementation can behave differently. Jython and IronPython use the
> garbage collectors from the JVM and .net, I don't know specifically how
> they behave.
>> My
>> understanding was (and I may well be wrong), that the reference count
>> does get decremented - in this case to 0 - but the *detection* of that
>> fact does not happen until the gc sweep looks through the heap for such
>> stale objects.
> That is how classic garbage collectors worked. And Python has something
> like that, but it's only used to collect circular structures, where the
> reference counts will never go to zero, but nevertheless the entire
> structure can be unreferenced as a whole.
>> --Ned.
>
Interesting. I haz a confuzed. Thanks for clearing that up.