[Python-Dev] Why aren't more things weak referencable

Christian Tismer tismer at stackless.com
Mon May 31 19:49:34 EDT 2004


Guido van Rossum wrote:

>>For strings at least, perhaps it is time to bite the bullet and
>>include weak reference support directly.  Weak reference support ups
>>the per string memory overhead from five words (ob_type, ob_refcnt,
>>ob_size, ob_shash, ob_sstate) to six.  The whole concept of weak
>>dictionaries is much more useful when strings can be used as keys
>>and/or values.
> 
> 
> Hmm... it is a high price to pay to add another word (*and* some extra
> code at dealloc time!) to every string object when very few apps need
> them and strings are about the most common data type.  And since
> they're immutable, what's the point of having weak refs to strings in
> the first place?  (Note that the original poster asked about
> *subclasses* of strings.)

Same here. I wouldnot vote to make strings or tuples or any other
tiny type weak-reffed in the first place.
Instead I would add the possible support to derived types, via
the __slot__ mechanism for instance.
There is a little coding necessary to make the generic code
handle the case of var-sized objects, but this is doable
and not very complicated.

This may be really needed or not. if we can create the rule
"every derived type *can* have weak-refs", this is simpler
to memorize than "well, most can, some cannot".

cheers -- chris

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