[Python-Dev] PEP 447: add type.locallookup (original) (raw)

Ronald Oussoren ronaldoussoren at mac.com
Thu Sep 19 12:32:38 CEST 2013

On 19 Sep, 2013, at 12:12, Nick Coghlan <ncoghlan at gmail.com> wrote:

On 19 Sep 2013 20:00, "Paul Moore" <p.f.moore at gmail.com> wrote: > > On 19 September 2013 10:32, Ronald Oussoren <ronaldoussoren at mac.com> wrote: > > The first time a method is called the bridge looks for an Objective-C selector > > with the same name and adds that to the class dictionary. This works fine for normal > > method lookups, by overriding getattribute, but causes problems with super: > > super happily ignores getattribute and peeks in the class dict which may > > not yet contain the name we're looking for and that can result in incorrect results > > (both incorrect AttributeErrors and totally incorrect results when the name is > > not yet present in the parent class' dict but is in the grandparent's dict). > > As an alternative approach, could you use a custom dict subclass as > the class dict, and catch the peeking in the class dict that > way? Or is this one of those places where only a real dict will do? Even Python 3 doesn't let you control the runtime type of the class dict, only the type used during evaluation of the class body.

Changing the class dict type from C is easy enough, but as you wrote below doing this gives you an interesting experience. Changing PyDict_* to call the subclass implementation of the corresponding slot would be easy enough, but that changes the behavior of a core CPython API and I wouldn't look forward to auditing the CPython code base to check if such a change is safe (let alone all other extensions). Some code will use the PyDict_* API instead of the abstract API because the former is faster, but at least some callers for PyDict_GetItem will do this to explicitly get the base class implementation.

Ronald

I've played with changing that - it makes for a rather special interpreter experience :) Cheers, Nick. > > Paul

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