On Sun, May 26, 2013 at 12:53 AM, Łukasz Langa <luk...@langa.pl> wrote: > On 25 maj 2013, at 16:08, PJ Eby <p...@telecommunity.com> wrote: > >> ISTM there should be some way to get at the raw >> registration info, perhaps by exposing a dictproxy for the registry. > > Is that really useful? Just today Antoine asked about changing > behaviour of __subclasses__(), suspecting it isn't used in real world > code anyway. What you're proposing is the functional equivalent of > __subclasses__(). > > If you need direct access to the registry, do you think the ability to > specify your own registry container isn't enough?
I'm actually wary about allowing that - letting people pass in the registry namespace the can alter it directly and thus bypass any extra code in register (such as setting the flag to enable the ABC support in the reference impl, or clearing the cache in PJE's suggested update). We don't allow custom namespaces for classes either. Sure, we allow them for the class *body*, but the contents of that get copied to a new dict when creating the class instance, precisely so we can ensure user code never gets a direct reference to the underlying mapping that defines the class behaviour. I actually patched Python once to to remove that copy operation while tinkering with the PEP 422 implementation. I wish I had kept a recording of the subsequent terminal session, as the terrible interactions with the method lookup caching were thoroughly confusing, but quite entertaining if you're into tinkering with programming languages :) So I think I'd prefer flipping this around - you can't provide a custom registry mapping, but you *can* get access to a read only view of it through a "registry" attribute on the generic function. >> The way to detect ABC registrations is via the >> ABCMeta._abc_invalidation_counter attribute: if its value is different >> than the previous value saved with the cache, the cache must be >> cleared, and the new value stored. > > Wow, I was looking at it just today morning and somehow missed how it > can be used. Great idea, I'll play around with it later today. Yeah, this is exactly how the ABC code itself uses it - sorry I wasn't clearer about why I suggested you look at the caching code for ABC instance and subtype checks :) Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
