[Cython] __getattribute__

[Robert Bradshaw]

On Apr 30, 2008, at 6:41 PM, Peter Todd wrote:

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> On Wed, Apr 30, 2008 at 06:17:31PM -0700, Robert Bradshaw wrote:
>> On Apr 29, 2008, at 5:42 PM, Peter Todd wrote:
>>
>>> Is there a __getattribute__ work-alike in Cython?
>>>
>>> Essentially I need direct control over an objects tp_getattro and
>>> tp_setattro slots to implement a wrapper class. Specificly
>>> wrapped.__class__ should go to the wrapped objects class attribute,
>>> not
>>> the wrapping objects __class__ attribute.
>>>
>>> __getattr__ outputs C-source that includes a call to
>>> PyObject_GenericGetAttr first, and won't run my code if that call
>>> succeeds.
>>>
>>> Thanks,
>>>
>>> Peter
>>
>> Not that I'm aware of, though I'd imagine that implementing
>> __getattribute__ (if it exists) as being called at the top of this
>> function would be fairly easy to do. One would want to match Python
>> symantics exactly.
>
> Thanks for the reply.
>
> I've been looking at the Cython source myself, and it looks doable,  
> I'll
> put some effort into implementing it.

Great!

> From what I can see I'd be
> updating generate_getattro_function() to do a scope.lookup_here() on
> '__getattribute__' first, if that succeeds, output code to call it,
> otherwise go on to the existing code.

Sounds like a good plan. Is __getattribute__ inherited?

>
> With the additional complication
> that if __getattribute__ is defined, as well as __getattr__, the  
> latter
> must be called if the former raises AttributeError.

Yep, it should go onto the existing code (or call the super/default  
getattribute) on an error, even if __getattr__ is not defined, to  
match the specs.

> Another question is I noticed that the latest cython-devel code emits
> warnings on usage of __new__, saying to use __cinit__ instead. I  
> take it
> there is planned work to make __new__ more like Python's __new__ and
> have it create the object as well? Again, that's another feature I  
> could
> really use.

Eventually we may implement this (I looked into it some, but it  
wasn't as straightforward as I had hoped), but using __cinit__ now is  
good to avoid the confusion.

> FWIW I'm writing a electrical design automation library called Tuke.
> Currently I have some C extension API code written to wrap objects in
> contexts, but would like to re-write that in Cython as well as  
> implement
> a whole lot of other basic functionality.
>
> http://github.com/retep/tuke/tree/master

Cool. Should I add this to http://wiki.cython.org/projects ?

- Robert

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