[Python-Dev] C basetype mapping protocol difference between 2.2.1 and 2.3

[Guido van Rossum]

> (gdb) p *self->ob_type->tp_as_mapping
> $2 = {mp_length = 0x4006eb7c <_ndarray_length>, mp_subscript = 0x80669b8 
> <slot_mp_subscript>,
> mp_ass_subscript = 0x80669e0 <slot_mp_ass_subscript>}
> 
> Looking at the same code compiled for Python-2.3, _ndarray "owns" all of 
> the mapping protocol slots, which is what I really want to happen:    
> 
> (gdb) p *o->ob_type->tp_as_mapping
> $1 = {mp_length = 0x400c1a68 <_ndarray_length>, mp_subscript = 
> 0x400c1a80 <_ndarray_subscript>, mp_ass_subscript = 0x400c1188 
> <_ndarray_ass_subscript>}
> 
> Did anything change between Python-2.2.1 and Python-2.3 that would 
> account for this?

Yes, I did several massive refactorings of a lot of very subtle code
in typeobject.c.  Note that this is only a performance improvement,
not a semantic change: slot_mp_subscript will look for and call the
__setitem__ descriptor in the type dict, which will be a Python
wrapper around _ndarray_subscript.  The new code notices that this is
so and leaves _ndarray_subscript in the slot.

I wish it was easy to backport this to 2.2.2, but it's not. :-(

--Guido van Rossum (home page: http://www.python.org/~guido/)