[Python-Dev] gc ideas -- sparse memory (original) (raw)

Dima Tisnek dimaqq at gmail.com
Sat Dec 4 06:47:53 CET 2010

On 3 December 2010 16:45, "Martin v. Löwis" <martin at v.loewis.de> wrote:

Oh my bad, I must've confused python with some research paper. Unique id is not so hard to make without an address.

While on this topic, what is the real need for unique ids? They are absolutely needed for mutable objects. For immutable ones, it would be ok to claim that they are identical if they are equal (assuming they support equality - which is tricky for things like NaN).

Indeed, but do ids really need to be unique and fixed at the same time?

a is b # (if atomic) needs unique ids, but doesn't really need fixed ids a[b] # needs fixed hash, but not strictly a globally unique id

I can imagine an implementaion of pickle for example that uses unique and fixed as a given to detect cycles, etc; but that would be implementation detail.

It seems to me unique and fixed id implies that it is stored somewhere (with incref beforehands and decref afterwards), however a proper reference to an object could be used just as well.

Am I still missing something?

Of course, the C API has lots of assumptions that identity and address are really the same thing. Regards, Martin

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