[C++-sig] boost.python: modifying class getattr

[Hans Meine]

On Wednesday 16 November 2005 18:37, David Abrahams wrote:
> > is there a way to modify the type object associated with Foo_ instances
> > so that instead of calling PyObject_GenericGetAttr when an attribute is
> > requested, Python calls a function
> > PyObject *
> > Foo_GetAttr(PyObject *obj, PyObject *name)
> > ?
>
>   PyTypeObject* Foo_t = (PyTypeObject*)Foo_.ptr();
>   Foo_t->tp_getattro = Foo_GetAttr;

Interesting.  In a desperate attempt to make accessing (2-dimensional) point 
elements from my Polygon class faster (a native python list of these objects 
is twice as fast), I tried to manually set (PyTypeObject*)Foo_.ptr() 
->tp_as_sequence->sq_item to my hand-crafted __getitem__ implementation... 
which made it *slower*. ;-)

Obviously, my __getitem__ using extract<Vector2Array>(self)() is doing an 
extra type-checking which my previously used boost::python function did not 
do (since boost knew that self contained my object), and - I should have had 
a little more confidence in the power of boost::python - was already 
registered in the special tp_as_sequence->sq_item slot (which triggered an 
assert I had put in before overwriting sq_item). ;-}

That's cool.  What a pity that I spent my afternoon trying to optimize where 
it was already done optimally. ;-/

Obviously, the only remaining advantage of a python list is that it contains 
readily-wrapped python objects that can simply be returned (after an 
incref())?!

-- 
Ciao, /  /
     /--/
    /  / ANS