[Python-Dev] special method lookup: how much do we care?

[Terry Reedy]

Benjamin Peterson wrote:
> 2009/5/8 Daniel Stutzbach <daniel at stutzbachenterprises.com>:
>> On Fri, May 8, 2009 at 6:14 PM, Benjamin Peterson <benjamin at python.org>
>> wrote:
>>> Normally special methods use slots of the PyTypeObject struct.
>>> typeobject.c looks up all those methods on Python classes correctly.
>>> In the case of __enter__ and __exit__, the compiler generates bytecode
>>> to look them up, and that bytecode use PyObject_Getattr.
>> Would this problem apply to all special methods that don't use a slot in
>> PyTypeObject, then?  I know of several other examples:
> 
> Yes. I didn't think of those.
> 
>> __reduce__
>> __setstate__
>> __reversed__
>> __length_hint__
>> __sizeof__
>>
>> (unless I misunderstand the definition of "special methods", which is
>> possible)

__reversed__, at least, is called by the reversed() builtin, so there is 
no LOAD_ATTR k (__reversed__) byte code.  So for that, the problem is 
reduced to accessing type(it).__reversed__ without going thru 
type(it).__getattribute__.  I would think that a function that did that 
would work for the others on the list (all 4?) that also have no 
LOAD_ATTR bytecode.  Would a modified version of object.__getattribute__ 
work?

tjr