[Python-Dev] PEP 447: hooking into super() attribute resolution (original) (raw)

Ronald Oussoren ronaldoussoren at mac.com
Mon Jul 15 18:56:56 CEST 2013

On 15 Jul, 2013, at 18:49, Guido van Rossum <guido at python.org> wrote:

A major open issue: the locallookup method could also be used for normal attribute resolution, but that probably causes issues with attribute caching (see the PEP for details). I haven't worked out yet if it is worthwhile to tweak the proposal to fix the caching issues (even though the proposal currently says that PyObjectGenericGetAttr will use the new method). Fixing the caching issue definitly would help in my primary use case by reducing code duplication, but might end up making the API unnecessarily complex. Hm. It looks like the functionality you actually want to hook into is in PyTypeLookup().

That's right. I didn't want to get too technical, but forgot to consider who are reading this :-)

I think that in this case the PEP's acceptance will be highly correlated with your ability to produce an actual patch that (a) implements exactly the functionality you want (never mind whether it matches the exact API currently proposed), and (b) doesn't slow down classes that don't provide this hook.

I'd only reall need the functional change to super(), but I am working on a patch that also changes _PyType_Lookup. I think I can avoid slowdown by making the tp_locallookup optional and only "punishing" those classes that use the new slot. A minor complication is that I'll have to change the interface of _PyType_Lookup, it currently returns a borrowed reference and will return a new reference. That's just careful bookkeeping though.

Other than that, I think that it's a laudable attempt at generalizing, and I hope you solve the implementation conundrum.

I was pleasantly surprised in how the changed API was cleaner and applicable to _PyType_Lookup as well. I guess that means I'm on the right path.

Ronald

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