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[Python-Dev] doc change for weakref

Steven D'Aprano steve at pearwood.info
Sat May 26 03:55:49 CEST 2012 
Ethan Furman wrote:
> I'd like to make a slight doc change for weakref to state (more or less):

What specific part of the docs are you planning to change?

My guess is that you want to change this start of the third paragraph:

http://docs.python.org/py3k/library/weakref.html

[quote]
A weak reference to an object is not enough to keep the object alive: when the 
only remaining references to a referent are weak references, garbage 
collection is free to destroy the referent and reuse its memory for something 
else.
[end quote]

I don't think that should be changed. It makes no promises except that weak 
refs won't keep an object alive. Everything else is an implementation detail, 
as it should be.


>    weakrefs are not invalidated when the strong refs
>    are gone, but rather when garbage collection
>    reclaims the object


I think you're making a distinction here that we should not make. Reference 
counting *is* a garbage collector (even if gc-bigots like to sneer at ref 
counting as "not a real gc"), and implementations with such a ref counting gc 
will not always distinguish the two states "strong refs are gone" and "object 
is reclaimed".

I don't believe that we need to make promises about the exact timing of when 
weak refs will be invalidated.


> Should this be accurate for all implementations, or should it be more 
> along the lines of:
> 
>    weakrefs may be invalidated as soon as the strong refs
>    are gone, but may last until garbage collection reclaims
>    the object

This is better than the previous suggestion, since it says "may" rather than 
implies a "will".


-- 
Steven
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